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The effect of a seasonal environment and fire on the ecology of frillneck lizards, Chlamydosaurus kingii, in the wet-dry tropics of
northern Australia.
by
Anthony D. Griffiths, B. Ed. (Env. Sci.) Faculty of Science
Northern Territory University Darwin
A thesis submitted to the Northern Territory University in fulfilment of the requirements for the degree of Master of Science.
November, 1994
Statement of Sources
This thesis is my original work and has not been submitted, in whole or in part, for a degree at any other University. Nor does it contain, to the best of my knowledge and belief, any material published or written by another person, except as acknowledged in the text.
Signed
Tony Griffiths
11
This work is dedicated to the memories of my mother Lou Griffiths and Alicia Johnson.
Acknowledgments
I would like to thank Dr Keith Christian for his supervision, technical support, and
constructive comments throughout the course of this project. His thoroughness and patience
during the writing of this thesis is of special note, and hopefully this will assist me in my
future endeavours.
My family and friends provided tremendous support and understanding. In particular, Ben
Scambary helped in so many small but important ways. Marisa Fontes played an
instrumental role in the maintenance of my sanity.
Logistical support in the form of fues and workshop space was provided by Kapalga
Research Station in Kakadu National Park. Robert Eager's generosity and helpful advice
were especially helpful, particularly during those long wet season days. My thanks to all
the fue crews for lighting the fires, and for keeping out all the unwanted ones. Many
volunteers ably assisted with fieldwork, too many to list here. Ajio Pereira and Gavin
Bedford gave considerable help in the laboratory constructing radio transmitters and
answering questions. Owen Price and Zhoa Yuen explained the intricies of GLIM.
Dick Braithwaite's generous nature and flexibility enabled me to keep myself financially
solvent during the course of this project. John Woinarski must also be thanked for putting
the idea of post-graduate study into my head in the fust place. Valuable comments on early
drafts of this thesis were provided by Keith Christian, John Woinarski, Dick Williams,
Gavin Bedford, Dave Bowman, Grant Farrell and Dick Braithwaite.
The project was partly funded by student travel grants from Australian Nature Conservation
Agency (ANCA), North Australia Research Unit student assistance scheme, and Australian
Geographic. Permission to work on frillnecks was given by Tropical Ecosystems Research
Centre and Northern Territory University Animal Ethics Committees. Permits were granted
by Conservation Commission of the Northern Territory and ANCA.
iii
Abstract
A population of Chlamydosaurus kingii, in Kakadu National Park, Northern Territory, was
· studied between April 1991 and April 1994. This species is a large, arboreal and
insectivorous agamid lizard which inhabits open forests and woodlands throughout northern
Australia. The principal aims of the study were to examine the ecological relationships
between this species and seasonal variation experienced in the wet-dry tropics, and the
frequent annual fires in this region. Additional information on the population dynamics and
the previously undocumented dry season ecology was also collected.
The study involved the telemetry and mark-recapture of C. kingii in Eucalypt dominant tall
open forest during the dry and wet seasons. All research was conducted within Kapalga
Research Station, where a landscape scale fire experiment was in progress.
Seasonal variation has a significant effect on the ecology of Chlamydosaurus kingii.
Frillneck lizards show a clear response to the prolonged dry season. This includes a
decrease in the volume of food taken, reduced activity and reduced seasonal growth. This
coincides with the selection of large Eucalyptus trees. Termites are a substantial part of
their diet during the dry season. The presence of termites in their diet is initially perplexing
given the "sit and wait" foraging behaviour of frillneck lizards, but the unique foraging
behaviour (above the ground during the day) exhibited by Australian Harvester termites
(Drepanotermes) allows frillneck lizards access to them when other food resources are
generally low. Growth is reduced in the dry season as a result of the lower volume of food
ingested. There is a general trend of energy conservation in the dry season. Male frillneck
lizards are able to maintain their body condition throughout the dry season, but their
lV
condition decreases at the commencement of the reproductive period. This presumably is
due to the increased energy expenditure associated with defending home ranges and sexual
activity. Females show considerably more variation in body condition, apparently related
to the production of eggs.
Fire is common throughout northern Australia. Frillneck lizards are able to survive fues
lit in the first few months of the dry season by remaining perched in trees. A higher level
of mortality occurs in the late dry season fues, along with a change in the behavioural
response to fire by sheltering in either larger trees or in hollow termite mounds. Food is
more accessible after fues due to the removal of ground vegetation. This is reflected in
greater volume and diversity of prey in stomach contents after fues. This increase is more
pronounced after late dry season fues, possibly due to the greater amount of ground
vegetation removed by these more intense fues.
During the dry season frillneck lizards prefer trees with a medium canopy cover located
in an area with a low density of grass. Fire has an effect on this relationship. Habitat which
has not been burnt for a number of years develops a denser layer of grass and possibly a
more continuous tree canopy cover, compared to annually burnt habitat Frillneck lizards
in habitats unburnt for a number of years tend to perch in trees with a smaller canopy.
Diets are generally similar among the three fire treatments. In general, fire influences the
habitat use of frillneck lizards by creating more heterogenous habitats, with more open
areas.
v
Frillneck lizards restrict their reproductive cycle to the wet season (summer months), as is
common with other agamids. The reproductive season begins prior to the onset of
monsoonal rains and the related increase in food availability. Hatchlings begin to emerge
during the period of highest food availability, although some late hatchings occur, and they
may experience greater difficulty in obtaining food. Male frillneck lizards grow faster than
females and have a larger body size. Males also maintain larger home ranges than females
in the dry season, which may ensure the presence of a number of females within their
home ranges. Only large males actively defend their home ranges. The low densities of
frillneck lizard in one site may be related to the absence of fire, and this may affect the
long-term viability of populations.
Vl
Relevant Publications
(copies attached at the end of the thesis)
Bedford, G.B., Christian, K.A. and Griffiths, A.D. ( 1 993). Preliminary investigations on
the reproduction of the frillneck lizard (Chlamydosaurus kingii) in the Northern Territory.
pp. 127- 1 3 1 . /n Lunney, D. and Ayers, D. (eds.), "Herpetology in Australia: A Diverse
Discipline". Transactions of the Royal Zoological Society of New South Wales. Surrey
Beatty and Sons, Sydney.
Attachment l
Vll
Table of Contents
Statement of Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (ii)
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (iii)
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (iv)
Relevant Publications . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (vii)
Table of Contents . . . . . . . . . . . . . . . ... . .. . . . . . . . . . . ... . . .. . . . . .. . . . . . . . (viii)
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (x)
List of Tables . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . .. . . .. . ... . .. . . (xvi)
Chapter 1 General Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 2 Seasonal ecology of the frillneck lizard, Chlamydosaurus kingii, in the wet-dry tropics of Australia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4 Diet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4 Food availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Body condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Seasonal growth rate and change in body mass . . . . . . . . . . . . . . . . . . . . . . 25 Habitat use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Seasonal activity index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Chapter 3 The short-term and longer-term effects of annual fue on the behaviour, diet, growth, and habitat use of the frillneck lizard, Chlamydosaurus kingii. . . . . . . 45
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
METHODS . . . . . . . . . ... . . . . . ... . . . . . . . . . . . . . . .. . . . . .. . . . . . .. . . . . . . . 47
Vlll
RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Short-term effects of fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Longer-term effects of flre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
DISCUSSION . . . . . . .. . . . . . . . . . . . . . . . .. .. .. . . . . . . . . . . . . . . .. . . . . . . . . . 81 Short-term effects of fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Longer-term effects of fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8
Chapter 4 The demography, population dynamics and dry season home range of frillneck lizards, with reference to the effects of three different ftre regimes. . . . . . . . . 89
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
METHODS . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . 91
RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Reproduction biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Growth and age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Population dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Home ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 16
Chapter 5 Synopsis and management implications. 1 1 8
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
lX
List of Figures
Figure 2 . 1 . A map showing the location of Kapalga Research Station, Kakadu National
Park within the Northern Territory, Australia. 7
Figure 2 . 2. A map showing the location of permanent study sites within Kapalga
Research Station, Kakadu National Park. 9
Figure 2.3. Monthly rainfall (mean of 3 sites ) recorded at Kapalga Research Station
(data from CSIRO's Division of Wildlife and Ecology). 15
Figure 2.4. The mean total volume of stomach contents (ml) over four seasonal periods.
Closed circles represent males, open circles represent females and numbers
are sample sizes. Error bars are one standard error. 16
Figure 2 .5. Relationship between total invertebrate abundance collected from sweep
netting at each site and the corresponding total rainfall for the previous three
months. 23
Figure 2.6. Mean residuals of linear regression of log-body mass with log-SVL for adult
frillneck lizards. Closed circles are adult males, open circles are adult
females, and numbers are sample sizes. Error bars are one standard error.
Line through zero represents the best least squares fit. 24
X
Figure 2.7. Seasonal growth rate (a,b) and change in body mass (c,d) relative to initial
body length. Closed circles are wet season values and open circles are dry
season values. 26
Figure 2.8. The mean height of trees (m) used by frillneck lizards in four seasonal
periods. Closed circles are telemetered lizards, open circles are non
telemetered lizards, numbers represent sample sizes. Error bars are one
standard error. 32
Figure 2.9. The mean trunk diameter (em) of trees used by frillneck lizards in four
seasonal periods. Closed circles are telemetered lizards, open circles are non
telemetered lizards, numbers represent sample sizes. Error bars are one
standard error. 33
Figure 2.10. The mean perch height (m) of frillneck lizards in four seasonal periods.
Closed circles are telemetered lizards, open circles are non-telemetered
lizards, numbers represent sample sizes. Error bars are one standard error.�
Figure 2.11. Monthly variation in number of lizards sighted or captured per kilometre
driven during routine censussing of sites. Numbers are the number of
censuses each month, and error bars are one standard error. 36
Figure 3.1. Location of three permanent fire treatment sites within Kapalga Research
XI
Station. The shaded areas represent each site. 49
Figure 3.2. Frequency distribution of the number of invertebrate orders and prey size
classes in the stomach contents of frillneck lizards, one week before and one
week after early dry season fire. Open bars represent before fire and closed
bars represent after fire. 59
Figure 3.3. Relative abundance and relative volume of prey taxa in stomach contents,
one week before and one week after early dry season fires. Open bars
represent before fire and closed bars represent after fire. Abbreviations for
prey taxa are: !so.- lsoptera; Orth.- Orthoptera; Hem. - Hemiptera; Col. -
Coleoptera; Dip. - Diptera; Lep. - Lepidoptera; Hym. - Hymenoptera; Blat. -
Blattodea; Mant.- Mantodea; Odon.- Odonata; Phas.- Phasmotodea; Aran.-
Aranea; Chi/. - Chilopoda. 60
Figure 3.4. Frequency distribution of the number of invertebrate orders and prey size
classes in the stomach contents of frillneck lizards, one week before and one
week after late dry season fires. Open bars represent before fire and closed
bars represent after fue. 62
Figure 3.5. Relative abundance and relative volume of prey taxa in stomach contents of
frillneck lizards, one week before and one week after late dry season fires.
Open bars represent before fire and closed bars represent after fire.
Abbreviations of prey taxa names follows Figure 3.3. 63
xu
Figure 3.6. The effect of significant variables in a logistic regression model of the
occupancy of trees by frillneck lizard during the dry season. The graphs
show changes in estimated probability of occurrence of frillneck lizards with
changes in (a) tree canopy cover; {b) the ground vegetation density at 25 em;
(c) trunk diameter; and (d) tree height. For each relationship the values of
other variables in the model are fixed at the mean value. For graphs {a) and
{b), solid lines represent the unburnt site, dashed lines are the early dry
season fire site and the dotted lines are the late dry season fire site. 69
Figure 3.7. Relative abundance of the number of prey size classes and invertebrate
orders present in the stomach contents of frillneck lizards for each fire
regime in the dry season. Open bars represent unbumt treatment, hatched
bars rising right are early ftre treatment and hatched bars rising left are the
late fire treatment. 72
Figure 3.8. Relative abundance of the number of prey size classes and invertebrate
orders in the stomach contents of frillneck lizards for each fire regime during
the wet seasons. Open bars represent unbumt, hatched bars rising right are
early fire treatment and hatched bars rising left are the late fire treatment. J
Figure 3.9. Mean residuals of linear regression of log-body mass with log-SVL for adult
male frillneck lizards in each of the fire treatments, during the dry and wet
Xlll
seasons. Numbers are sample sizes and error bars are one standard error.
Line through zero represents the best least squares fit. 79
Figure 3.10. Mean residuals of linear regression of log-body mass with log-SVL for adult
female frillneck lizards in each of the fire treatments, during the dry and wet
seasons. Numbers are sample sizes and error bars are one standard error.
Line through zero represents the best least squares fit. 80
Figure 4.1. The percentage of home range estimated from the cumulative number of
locations collected in the dry season. Approximately eight locations are
needed to describe 80% of a frillneck lizards' dry season home range. 94
Figure 4.2. The number of gravid and non-gravid female frillneck lizards captured each
month during the wet season. Both reproductive seasons are combined. 96
Figure 4.3. Growth rate of male and female frillneck lizards. The mid-point of SVL
between first and last recapture is used. Open circles represent males and
closed circles represent females. 99
Figure 4.4. Number of lizards in the different size cohorts within each fire treatment site.
Open bars represent females, closed bars represent males and lined bars
represent juveniles and hatchlings. 102
Figure 4.5. Mean monthly capture rates of males (circles) and female (squares) frillneck
XIV
lizards. All sites and years have been combined. 104
Figure 4.6. Proportion of adult male frillneck lizards with scars for four size classes in
each of the fire treatment sites. Triangles represent the late fire site, squares
represent the early ftre site and circles represent the unburnt site. 108
XV
Table 2 . 1
List of Tables
Occurrence, relative abundance and relative volume of prey taxa present in
stomach samples of C. kingii during the dry and wet seasons. 1 8
Table 2.2. The number and relative abundance (lk) of invertebrate orders from sweep-
Table 2.3.
Table 2.4.
Table 2.5.
Table 3 .1 .
netting during the dry and wet seasons. 2 1
Mean and standard error of seasonal growth rate as measured by changes in
SVL (mm day"1) and change in body mass (% g day"1) for male and female
frillneck lizards in the wet and dry seasons. Numbers in parentheses are
sample sizes. 27
The relative abundance (%) of tree species used by telemetered and non
telemetered frillneck lizards during the wet and dry seasons, and the relative
abundance (%) of tree species available in the field as determined by a
random walk technique. 30
A summary of tropical insectivorous lizard's foraging strategy, habitat, and
relative abundance of ants and termites in their diets. 40
Post-fire selection of habitat by telemetered frillneck lizards. All lizards were
monitored adjacent to burnt or unburnt habitat after the early and late dry
season fires during 1991. 65
XVI
Table 3.2.
Table 3.3.
Table 3.4.
Table 3.5.
Table 3.6.
Means ± one standard error of habitat structure variables used for the logistic
regression model. Data describing habitat structure of open forests were
collected from each flre treatment site. Occupied trees were known to contain
frillneck lizards, and unoccupied trees randomly selected trees were assumed
not to contain frillneck lizards. 66
Logistic regression model for occupancy of trees by telemetered frillneck
lizards during the dry season. X2 values refer to difference in scaled deviance
from total deviance of the null model. The 'k total deviance is the proportion
of scaled deviance from the total deviance of the null model. Treatment (site)
factors are represented in the model by: ( 1 ) early dry season site; (2) late dry
season site; and (3) unburnt site. 67
Selectivity indices for tree species used by frillneck lizards within each site
during the wet and dry seasons. 71
Dry season stomach contents of frillneck lizards from the three ftre treatment
sites. 75
Wet season stomach contents of frillneck lizards from the three fire treatment
sites. 76
xvu
Table 3.7.
Table 4.1.
Table 4.2.
Table 4.3.
Table 4.4.
Relative abundance of invertebrate orders obtained from sweep-netting in
each of the three fire treatment sites, during the dry and wet seasons.
Samples from both years are combined. Taxa denoted with ( --) were not
recorded from sweep-netting but were recorded in the stomach contents of
frillneck lizards. 78
Observed and expected capture frequencies, population estimates and
"goodness of fit" test for the early fire site. 105
Observed and expected capture frequencies, population estimates and
"goodness of fit" test for the late fire site. 105
Observed and expected capture frequencies, population estimates for the
unburnt site. The "goodness of fit" test was not possible due to the low
number of recaptures. 106
Dry season home range and movement for telemetered male and female
frillneck lizards in each of three fire sites. 109
XVlll
Chapter 1
General Introduction
Approximately 270 terrestrial reptile species are known from the northwestern region of
Australia (Woinarski and Braithwaite 1991). Much of this region is sparsely populated and
relatively undisturbed by European settlement. The terrestrial reptiles of this region
experience consistently high ambient temperatures, an annual cycle of high rainfall in the
summer months and a prolonged dry period. This creates a unique set of environmental
conditions to study terrestrial reptiles.
Lizards comprise a large component of this terrestrial reptile fauna. Research on the
population ecology of terrestrial lizard species in this region is sadly lacking. Previous
population ecology studies have made important contributions in establishing a range of
ecological relationships (Shine 1986, James and Shine 1988, Shine and Lambeck 1989).
However, the population ecology of the majority of lizard species and their relationships
with current ecological theories remain unknown.
The frillneck lizard, Chlamydosaurus kingii (Sauria: Agamidae), is possibly the most
recognisable member of the lizard fauna of this region. Its presence on the now defunct
two cent coin, innumerable post cards and tourist brochures has made it into an unofficial
faunal emblem of northern Australia. It has an extensive distribution in northern Australian
extending from the west to the east coast, and into the southern part of Papua New Guinea
(Cogger 1992). Shine and Lambeck ( 1989) described the general ecology of this species.
1
This thesis is presented in four chapters. Chapters two, three, and four and are written as
individual papers and examine a range of ecological relationships between C. kingii, its
environment and other taxonomically related lizard species. The fifth chapter presents a
synopsis of the three previous chapters, along with some management implications arising
from this research. A brief description of each chapter is given below.
Chapter two examines the seasonal variation in the ecology of C. kingii. Dry season
ecology of this species was previously undocumented, mainly due to the cryptic nature of
its behaviour during this period. By monitoring lizards throughout the year, it is possible
to determine and document the seasonal ecological changes. This information will provide
comparative information for future studies of seasonal variation in terrestrial reptile ecology
in the wet-dry tropics of Australia.
Chapter three investigates the short-term and longer-term effects of annual fires on the
ecology of C. kingii. Much of the open forest inhabited by frillneck lizards is regularly
burnt during the dry season. Questions pertaining to how lizards survive these fires and the
effects of ftre on their diet and habitat selection in the subsequent weeks are examined in
the ftrst half of this chapter. The longer-term effects on diet, habitat use and body condition
are considered in the second half of this chapter. By examining these aspects of the
frillneck lizard ecology, it is then possible to consider the relative importance of fire on
these factors, and whether this may effect the management of this species in northern
Australia.
2
Chapter four presents data pertaining to the demographics, population dynamics and dry
season home ranges of frillneck lizards. This chapter also compares the information from
frillneck lizards to the life history of other large Australian agamids. The effect of fire on
the population dynamics is also examined.
Chapter 5 presents a brief synopsis of the conclusions presented in the previous chapters.
This will include both general and noteworthy results of the ecology and life history
strategies of C. kingii in the wet-dry tropics of Australia. Management of this species, in
the light of information presented in this thesis, is briefly discussed.
3
Chapter 2
Seasonal ecology of the frillneck lizard, Chlamydosaurus kingii, in the
wet-dry tropics of Australia.
INTRODUCTION
Seasonal variation in temperate and arid habitats has a significant effect on the activity,
reproduction, resource acquisition, growth and habitat use of lizards (Dunham 1978,
Ballinger and Congdon 1980, Rose 198 1 , Andrews 1982, Paulissen 1988). Comparative
studies of lizard ecology and life history at the family level (predominantly lguanids) in
these habitats have contributed significantly to current theories of life history strategies and
general ecology (see Huey et a/. 1983, Pianka 1986).
The understanding of the seasonal ecology of reptiles in the seasonal tropics is poor.
Constant high ambient temperatures and high periodic annual rainfall combine to create a
unique environment for reptiles. Studies of tropical l izard ecology have encompassed a
variety of habitats (tropical savannas to closed rainforest) in several families, and they have
revealed a surprising diversity of responses to seasonal variation (Sexton et a/. 1972,
Aeming and Hooker 1975, Huey et a/. 1977, Christian et a/. 1983, Floyd and Jenssen
1983, Vitt 199la, Vitt 199 1 b, Vitt and Blackburn 199 1 , Bullock et a/. 1993, van Marken
Lichtenbelt 1993, van Marken Lichtenbelt et a!. 1993). This diversity and the relatively
small number of studies limit tests of current ecological theories in tropical habitats.
Previous studies of lizard ecology in the wet-dry tropics of northern Australia are few
4
considering the high species diversity of the region. Seasonal variation in diet (James et
a/. 1984, Shine 1986), reproductive strategy (James and Shine 1985, James and Shine
1988), and thermoregulation and energetics (Christian and Green 1994, Christian and
Bedford 1995) have provided a number of hypotheses relating to the evolution of certain
life history strategies for lizards in this region.
Frillneck lizards inhabit open forests and woodlands of the wet-dry tropics of Australia, and
on the east coast they extend into the temperate climate zone (Cogger 1992). The general
ecology of this species was studied by Shine and Lam beck ( 1989), but their field data is
exclusively from the wet season. They revealed a diurnal, arboreal, "sit-and-wait"
insectivorous lizard. Reproduction occurs exclusively during the wet season, and the lizards
reduce activity during the dry season. They are sexually dimorphic in body size with adult
males considerably larger than adult females. Frillneck lizards exhibit a significant
reduction in body temperature, field metabolic rate and water turnover during the dry
season (Christian and Green 1994, Christian and Bedford 1995).
The principal aim of this chapter is to establish how the ecology of the frillneck lizard
changes between the wet and dry seasons, in light of the changes in their physiology and
the environment. The specific aspects of their ecology considered in this chapter are: diet
and food availability; body condition and growth rate; habitat use; and their seasonal
activity. The relative importance of the effect of each environmental factor (e.g.
temperature, relative humidity) on the ecology of frillneck lizards is difficult to determine
due to the interdependent relationships of these factors. However, an assessment of the
strategies used by C. kingii in relation to other lizard species is possible.
5
METHODS
Site
All field work was done between April 1991 and April 1994 at Kapalga Research Station
(CSIRO Division of Wildlife and Ecology) in Kakadu National Park (12Q 43' S, 132Q 26'
E), 250 km east of Darwin, Northern Territory, Australia (Figure 2.1). This region
experiences a distinct seasonal wet-dry climate. The wet season in Kakadu National Park
(October to April) is characterised by high maximum (35"C) and minimum (24.C) air
temperatures, high relative humidity (60% at 0900 hrs) and high rainfall (1480 mm) (13
year averages from the Jabiru airport, Bureau of Meteorology). Rainfall is irregular and
relatively low during the first months of the wet season (early wet season; October to
December), becoming more consistent and relatively higher during the second half (late wet
season; January to April). The dry season (May to September) is characterised by high
maximum (33.C) but lower minimum (l9.C) air temperatures, lower relative humidity, and
little or no rainfall (Bureau of Meteorology). The dry season may also be divided into an
early dry season (May to July) when the soil and vegetation begin to dry out after the
cessation of monsoonal rains, and a late dry season (August to September) when conditions
are extremely dry.
The study was conducted in open forest dominated by Eucalyptus tetrodonta, E. miniata,
E. porrecta and Erythrophleum chlorostachys, with an understorey dominated by annual
grass Sorghum spp. The study area was based around a network of roads to facilitate the
censussing of lizards. Data were collected at three separate sites and they ranged in
6
�0 KAPALGA RESEARCH STATION
0
ARNHEM LAND
50 100
kilometres
Figure 2.1. A map showing the location of Kapalga Research Station, Kakadu National Park
within the Northern Territory, Australia.
7
area from 400 to 500 ha (Figure 2.2). Each site was subjected to a different fire regime.
but this will be discussed in Chapter 3. For this Chapter, the three sites are examined
together as one site.
Sampling
All frill neck lizards were originally sighted by driving slowly ( < 30 km hr-1) along the
roads, and either caught by hand or by a noose attached to a telescoping pole. At the initial
capture, each lizard was given a unique identifying number with a transponder (Destron®
IDI) implanted sub-cutaneously under a loose fold of skin in the neck area. At each capture
the following data were recorded: date; time; mass to the nearest g using an electronic
balance (Bonso®); and the snout-vent length (SVL) to the nearest mm using a perspex
ruler. Lizards were released at the exact point of capture within two hours of capture. All
field work was done between 0700 and 2000 hours.
A sub-sample of adult lizards (n = 55) was fitted with small radio-transmitters to assist in
data collection. Location transmitters (Biotrack SS-1 and Biotel TX-1) weighing
approximately 15 g (2-6% of lizard body mass) were attached to the tail using a small
amount of glue and adhesive bandage. After fitting of transmitters, lizards were released
at the exact point of capture within two to twelve hours. Telemetered animals were
relocated a minimum of twice a month, and transmitters were changed every three months
to replace the batteries. Animals were monitored for varying periods over the study period
due to movement out of transmission range, battery failure and predation.
8
N
0 5
km
c:::::I Permanent study sites
Figure 2.2. A map showing the location of study sites within Kapalga Research Station,
Kakadu National Park.
9
The mark-recapture and telemetry study provided data on diet, body condition, seasonal
growth, habitat use and activity. Rainfall data were collected fortnightly at each site by the
CSIRO Division of Wildlife and Ecology.
Diet
At initial capture (after April 1992) lizards with a SVL greater than 150 mm were stomach
flushed. Lizards were restrained on a wooden board using velcro strips, and a padded
plastic ring was placed in their jaws to hold their mouth open. One end of a plastic tube
(diameter = 3 mm, length = 25 em) was positioned into the stomach via the mouth, and
the other end was fitted to a 60 ml syringe filled with freshwater. The stomach was then
filled with approximately 40 ml of freshwater, while the abdomen was palped, and then the
animal was inverted. The stomach contents were collected with a permeable cloth stretched
over a bucket. Stomach contents were stored in 70% ethyl alcohol for later analysis.
Lizards recaptured within less than 6 months of the previous capture were not stomach
flushed.
Stomach contents were classified to order using a dissecting microscope. Each prey item
was assigned to one of five size classes by length (0-5 mm; 6-10 mm; 11-15 mm; 16-20
nun; > 20 mm). The volume for each prey taxa was estimated by the volumetric
displacement (in a graduated measuring cylinder± 0.1 ml) of a representative sub-samples
from each of the five size classes, and then all sizes classes were added together. The total
volume (ml) of stomach contents were measured by volumetric displacement of the whole
wet sample in a graduated measuring cylinder (± 0.1 ml).
10
Food availability was measured by sweep-netting the ground foliage (0-2 m above the
ground) for invertebrates (Stamps and Tanaka 1981) every three months at each site. Ten
samples of 30 sweeps were collected for each sampling period (total of 900 sweeps per
sampling period). Samples were collected along line transects, and no foliage was swept
twice. The contents of the net were placed in resealable plastic bags and preserved in 70%
ethyl alcohol. Samples were later sorted to the level of order, and into five size classes (as
with stomach contents).
Habitat
Data from the following habitat variables were collected at each capture or sighting of C.
kingii; tree species; tree height (m) and perch height (m) of the lizard, using a clinometer
(Suunto®); trunk diameter (em) at breast height using a calibrated tape measure. An
estimate of the frequency distribution of tree species in the study area was determined
using a random walk sampling method (Goldsmith and Harrison 1976). A minimum
distance of 30 m between each sampling point was set to avoid concentration of samples
within a confined area.
Analyses
Some seasonal analyses were done by dividing the data into dry (May to September) and
wet seasons (October to April), but when sample sizes were large and evenly spread across
the year, four seasons were used: late wet (January to March); early dry (April to June);
late dry (July to September); and early wet (October to December).
11
Diet
Diets were analysed using four measures: ( 1) the total volume (ml) of stomach contents;
(2) the relative abundance(%) of total prey items; (3) the relative volume(%) of prey taxa;
and (4) the occurrence (%) of one or more items of a particular prey taxon in the stomach
contents. Differences in the total volume of stomach contents between sexes and in
different seasons were compared using two-way ANOV A. Tukey's comparison of means
test was used to determine significant differences among seasons. A non-parametric Mann
Whitney U-test was needed to test for seasonal differences in the number of prey orders
and size classes due to the non-normal distributions. Seasonal differences in the abundance
of prey taxa in the stomach contents, and the availability of prey in the field were analysed
using contingency tables. The relative volume of prey taxa was analysed using a
Kolmogorov-Srnirnov non-parametric test. Simpson's Diversity index (D) was used to
determine seasonal changes in dietary diversity:
D = 1 - I,( <pi )2
where <pi is either relative abundance or relative volume of each prey taxa in the stomach
contents. This index ranges from 0 (low diversity) to a maximum of ( 1 - 1/S), where S is
the number of prey taxa (Krebs 1985).
Body condition
Body condition was determined by plotting log10 transformed body mass against log1o
transformed SVL of adult male (SVL > 230 mm) and non-gravid adult female (SVL > 175
nun). A linear regression was applied to these data, giving a mean body condition for the
total sample. The residual deviation from the regression is indicative of an individual's
body condition, corrected for different body lengths (James 1991a). Differences between
12
sexes were determined using an unpaired t-test, and a one-way ANOV A was used to test
for seasonal differences in the mean residual deviations.
Seasonal growth and change in body mass
Seasonal growth rates and change in body mass were calculated from lizards caught more
than twice within a single dry (May to September) or a single wet season (October to
April) period. Seasonal growth rates were determined by dividing the change in SVL by
the number of days between the fust and last capture (within a single season). Recaptures
of less than one week were excluded. The concurrent change in body mass over the same
period was also determined. The change in body mass was divided by the number of days
between the first and last capture within a single season, and this number was divided by
the initial body mass and expressed as a percentage. Seasonal differences in both seasonal
growth and change in body mass were tested using ANCOVA with SVL as covariate.
Habitat use
Contingency table analysis tested for differences in the relative frequency of tree species
used by frillneck lizards between seasons. Seasonal differences in the habitat use of lizards
(tree height, trunk diameter and lizard perch height) were analysed using one-way ANOVA.
Seasonal activity index
An index of activity was calculated by dividing the total number of lizards either sighted
or captured in daily car censuses by the number of kilometres driven during each field
census. This index is an indirect measurement of the population's general activity, not
13
an individual animal's activity. Censuses were pooled into four seasons and tested by
Kruskal-Wallis one-way ANOV A.
All means are presented with one standard error unless specified.
RESULTS
Rainfall
Rainfall from Kapalga Research Station over the course of this study is illustrated in Figure
2.3. The onset of monsoonal rains occurred in November of each year, apart from the
1991-92 wet season where the first rains were delayed until December. The highest
monthly rainfall was recorded in January or February of each year (Figure 2.3). The
cessation of rainfall was similar among the consecutive wet seasons, with minimal rainfall
occurring after April in each year. Total rainfall for the 1991-92, 1992-93, 1993-94 wet
seasons were 1116 mm, 1410 mm, and 1307 mm, respectively.
Diet
A total of 226 stomach content samples were collected b�tween May 1992 and April 1994.
A distinct reduction in total volume of stomach contents in both sexes occurred in the early
dry season, after the relatively high total volume recorded in the early and late wet seasons
(Figure 2.4). The total volumes of stomach contents of females is greater than males in the
first six months of the year (late wet and early dry season), whereas this relationship is
reversed in the later half of the year (late dry and early wet season) with males recording
a greater total volume than females (Figure 2.4). A two-way ANOV A for sex and seasons,
14
600 ....
500 .... -E E 4oo � -
� 300 -·-
ns � 200 -
1 00 -
o �T��--��-��·�����.�� Jan. July
1 991
Dec. July Dec.
1 992
.Months
July 1 993
Dec.
Figure 2.3. Monthly rainfall (mean of 3 sites) recorded at Kapalga Research Station (data
from CSIRO's Division of Wildlife and Ecology).
1 5
£ 9 (/) ..... c Q) c 8 0 u
-5 7 ro E 0 ..... 6 (/)
� 0
� 5 :J 0 > 4 ro ..... 0 ..... 3 c ro Q)
14 1 3 \ \
\
T T 35 r 1 7 - / l a1 / _
t / --027 1 1 1 � 2 ....._--r---,-----.---�--
late wet early dry late dry early wet
Seasons
Figure 2.4. The mean total volume of stomach contents (ml) over four seasonal periods.
Closed circles represent males, open circles represent females and numbers are sample
sizes. Error bars are one standard error.
16
was significant for seasons only (seasons, F3•194 = 3.38, P = 0.02). Neither sex or the
interaction between sex and season was significant (sex, F1•194 = 0.01, P = 0.92; sex x
season, F3.194 = 0.3 1 , P = 0.81). Tukey's comparison of means test on seasons indicated the
early dry season mean total volume of the stomach contents was significantly lower than
both early and late wet season means, although the late dry season mean was not
significantly different from any of the other seasonal periods. The correlation between SVL
and total volume for dry season stomach samples was non-significant (r = -0.06, P = 0.48,
n = 144). However, the correlation between SVL and wet season total volume indicated
a weak but significant relationship for both sexes combined (r = 0.23, P = 0.03, n = 82).
Preliminary analyses revealed no significant differences between sexes in the number of
prey taxa, the number of size classes of prey or the taxonomic composition of the diet,
therefore the results presented here are for both sexes combined. Table 2.1 summarises the
occurrence, relative abundance and relative volume of prey taxa for stomach contents of
C. kingii for the dry and wet seasons.
A total of 1 5 invertebrate orders were recorded from 144 dry season stomach samples.
Stomachs contained a mean of 2.85 ± 0.12 invertebrate orders and a mean of 77.85 ± 9. 15
items. A total of 15 invertebrate orders were recorded from 82 wet season stomach
samples. Stomachs contained a mean of 3.96 ± 0.19 prey taxa and a mean of 79.62 ± 1 1 .75
prey items. The number of prey orders per stomach sample is a broad indicator of the
diversity of prey taxa in C. kingii diet, and the wet season diet contained significantly more
orders (Mann-Whitney U-test: z = 4.79, P < 0.000 1) . There was no significant
17
Table 2.1. Occurrence, relative abundance and relative volume of prey taxa present in stomach samples of C.kingii during the dry and wet seasons.
Dry season Wet season
Prey taxa Occurrence Abundance Volume Occurrence Abundance Volume (%) (%) (%) (%) (%) (%)
Isoptera 36.8 73.3 33.6 57.0 76.8 20.0 Onhopetra 25.7 0.5 15.9 32.9 0.6 9.2
Hemiptera 27.8 0.8 3.8 12.2 1.0 2.3
Coleoptera 18.7 0.6 3.4 5 1 . 2 1 .7 3.9
Diptera 5.5 0 . 1 1 . 4 5.7 0.2 0.4 Lepidoptera 25.0 0.4 3 . 7 59.7 9 . 1 40.4 Hymenoptera 66.7 23.4 5.2 68.3 8.9 2. 1
Blanodea 4.2 0 . 1 1 . 1 6.1 0.2 0.3
Mantodea 1 . 4 0.01 1 . 0 1 .2 0.01 0. 1
Odonata 2 . 8 0.04 1 . 9 6 . 1 0. 1 2.7
Phasmotodea 6.9 0 . 1 3.6 3.7 0.05 0.5
Aranea 9.0 0 . 1 1 . 6 13.4 0.4 0.5 Plecoptera 2 . 8 0 . 1 1 . 1 1 . 2 0.01 0.4
Chilopoda 30.5 0.5 2 1 . 8 36.6 0.8 1 6 . 1
Gastropoda 2 . 8 0.03 0.6 7.3 0 . 1 0.8
other 1 . 4 0.02 0.3 2.4 0.03 0.3
totals n = 144 n = 1 12 1 2 445 (ml) n = 82 n = 6529 762 (ml)
Simpson's Diversity Index 0.635 0. 808 0.393 0.759
18
difference in the total number of items per stomach between wet and dry season samples
(t = 0.73, DF = 226, P = 0.43).
The relative abundance of prey taxa in the dry season was dominated by the order isoptera,
comprising 73.3% of all items present. Only one species of isoptera was identified from
these stomach samples, Drepanotermes rubriceps (A. Anderson, personal communication),
and most of these were soldiers. There is some taxonomic confusion within this genus, and
these termites will be referred to as Drepanotermes. Drepanotermes occurred in 36.8% of
the dry season stomachs samples, representing 33.6% of the relative volume. Another
important dry season prey taxon in the stomach samples was chilopoda (centipedes). The
low relative abundance of chilopoda (< 1 %), is misrepresentative of its importance as a
food item for frillneck lizards. Most chilopoda present in stomach samples (77%) had a
large body length (> 20 mm), and therefore the relative volume of 21.8% is more
indicative of the importance of centipedes in the dry season diet. Similarly, orthoptera
comprised 14.9% of the relative volume, although relative abundance was low (0.5%).
Hymenoptera exhibited a high relative abundance, comprising 23.4% of the total number
of prey items taken and was the most corrunon prey taxon in the dry season stomach
samples (66.7% occurrence). However, due to the small body length of ants (< 5 rrun), they
comprised only 5.17% of the relative volume.
Dietary composition during the wet season was dominated by three prey taxa: Iepidoptera,
isoptera and chilopoda (Table 2.1). Lepidoptera were present in a high proportion of
stomachs (59.7%), and contributed substantially to the relative volume (40.4%). All
Iepidoptera in the stomach samples were larvae, of which 37.2% were between 15-20 rrun
19
•
in length and 29.3% were longer than 20 mm. The relative volume of isoptera was reduced
in the wet season samples, compared to the dry season, probably due to the high volume
of Iepidoptera. Hymenoptera occur in a high proportion of samples in all seasons, but the
contribution to the relative volume of the diet remained small.
The relative abundance of prey taxa differed significantly between the wet and dry seasons
(X2 = 1428.54, DF = 7, P < 0.000 1) . The relative volume of various prey taxa also differed
significantly between the wet and dry seasons (Kolmogorov-Smirnov: D = 0.23, DF = 14,
P = 0.0 14). Inspection of Table 2. 1 indicates that the variation in relative abundance and
relative volume of hymenoptera, Iepidoptera and isoptera accounts for much of the
difference between the two seasons. S impson's diversity index of the relative volume
suggests a similar diversity of prey taxa present in the dry and wet seasons (Table 2. 1 ).
The diversity index of the relative abundance of prey taxa suggests that stomach samples
collected during dry season contain a higher diversity of prey taxa than wet season
samples.
Food availability
Table 2.2 shows the total number and relative abundance of invertebrate orders collected
from sweep-netting over two years. Each sample period is the sum of three pennanent
sites. A total of 12 invertebrate orders were collected using this method. It should be noted
that this method of sampling (sweep-netting) failed to sample some important invertebrate
orders that were present in stomach samples of Chlamydosaurus, namely isoptera and
chilopoda. There were fewer orders of invertebrates in the dry season samples, compared
to wet season samples. Dry season samples contained a high relative abundance of
20
Table 2 .2. The number anu relative abunuance (%) of invertebrate oruers from sweep-netting during the ury anu wet seasons.
I nvertebrate Dry season Wet season Dry season Wet season orders
Mt�y August Decem her March June 1993 August 1993 N ovemher February 1994 1 992 1992 1992 1 993 1993
No. % No. % No. % No. % No. % No. % Nn. % No. %
Isopter<� -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Orthopetra 32 10.6 32 16 .9 1 3 1 24.2 142 14.R 23 5 . 5 1 5 5 . 3 2 2 1 43 . 1 235 22.R
Hemiptera 58 19. 1 2 1 I I . I 40 7.4 82 8 . 5 40 9.(1 34 1 2 . 1 1 9 3 . 7 R(i X . 3 Coleoptert� 37 1 2.2 20 I 0. () I M 30.3 2 1 7 22.(1 7X I X . 7 22 7.8 6 1 1 1 .9 2 1 1 20 .4
Diptera 8 2.6 1 8 9.5 48 8.9 50 5 . 2 40 9.6 43 1 5 .3 35 (i . 8 7 1 6.9
Lepidoptera 7 2.3 3 1 . 6 50 9 . 2 1 14 I I .9 7 1 . 7 I 0.3 4 0.8 24 2 .3 H yrnenoptera 89 29.4 7 1 37.6 7 1 1 3 . I 1 30 1 3 . 5 1 9 1 45.8 1 2 5 44.5 99 1 9 . 3 1 8 3 1 7 . 7
Blattodea -- -- -- -- 5 0.9 1 3 1 .4 -- -- I 0.4 2 0.4 22 2 . 1
Mantodea I 0.3 I 0.5 I 0.2 1 II. I -- -- -- -- -- -- I 0 . 1 Ouonata 4 1 . 3 3 1 . (> 3 0.6 39 4.0 X I .9 I 11.4 I 0.2 4 0.4
Phasmotouea () 2.0 I 0/5 -- -- 20 2 . 1 I 0 .2 -- -- I 0.2 107 I 11.4
Aranea 62 20.5 29 1 5.3 2X 5.2 1 4(> 1 5 . 2 29 7.0 49 1 7 . 4 (17 1 3 . 1 1 6 l .(l
Plccoprcra -- -- -- -- 1 0.2 7 O.X -- -- -- -- I 0 .2 -- --
Chilopodt� -- -- -- -- -- -- -- -- -- -- -- . - -- -- -- --
Gastropod<� -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Total No. items 303 100 1 89 100 542 100 961 100 4 1 7 1 00 2 X I 100 5 1 3 1 00 1032 100
("' I
hymenoptera, orthoptera, aranea, hemiptera and coleoptera (Table 2.2). Wet season samples
contained a high relative abundance of orthoptera, coleoptera and hymenoptera (Table 2.2).
Invertebrates were most abundant in the wet season samples. A two-way ANOV A of total
abundance of invertebrates by site and seasons ( wet and dry) gave a non-significant result
for the interaction site x season (F2.18= 1.75, P = 0.203) and among the three sites (F2_18=
2.49, P = 0. 1 1 1) . However, the total abundance of invertebrates collected from sweep
netting was significantly greater in the wet season than during the dry season (Fu8= 27.19,
p < 0.000 1) .
There was a strong correlation between total invertebrate abundance at each of the three
sites for the 8 sampling periods and total rainfall for the previous three months at each site
(r = 0.83, P < 0.000 1 , n = 24) ( Figure 2.5). The discontinuous nature of this relationship
is due to the intense rainfall experienced during the three wet season months (January,
February and March), and the relatively low rainfall in the remaining months.
Body condition
The body mass at a given SVL of adult males was significantly larger than adult females
(t = 3.27, OF = 372, P = 0.001). Therefore, body condition was analysed in separate linear
regressions for males and females. Male body condition differed significantly among the
four seasonal periods (F3•273 = 3.38, P = 0.019) (Figure 2.6). Tukey's comparison
22
400
0) (..) c -§ 300 c �
..0 ro •
_.. • � 200 (J)
• • c •
ro • _..
� 1 00 • • • •
• •
•
0 0 200
• •
•
400 600 800
Rainfall (mm)
• •
• •
1 000 1 200
Figure 2.5. Relationship between total invertebrate abundance collected from sweep-netting
at each site and the corresponding total rainfall for the previous three months.
23
.050
.025 T CJ) 35 -
ro �
lag � - ----= -"'0 41 - 31 - -l74 CJ) 0.000 (1) cc
-.025 1
-.050
late wet early dry late dry early wet
Seasons
Figure 2.6. Mean residuals o f linear regression o f log-body mass with log-SVL for adult
frillneck lizards. Closed circles are adult males, open circles are adult females, and
numbers are sample sizes. Error bars are one standard error. Line through zero
represents the best least squares fit.
24
of means test indicated that the early wet season sample mean was significantly lower than
other three periods. Male body condition remained constant throughout both dry season
periods. Female body condition also differed significantly among the four seasonal periods
(Figure 2.6) (F3.110 = 3 . 14, P = 0.028). Tukey's comparison of means test indicated two
groups of significantly different mean residuals, group one included the early wet and early
dry seasons with relatively high residuals, while the second group included the late wet and
late dry seasons with low residuals.
Seasonal growth rate and change in body mass
The seasonal growth rates of male and female lizards were small for individuals recaptured
during the dry season (Figure 2.7, Table 2.3). Individuals recaptured within the wet season
exhibited higher seasonal growth rates (Figure 2.7, Table 2.3). However, seasonal growth
rates of large adult lizards (males SVL > 240 mm, females SVL > 2 1 0 mm) during the
wet season were negligible (Figure 2.7). These individuals have either reached or are close
to their maximum body size, and growth thereafter is reduced. There was no significant
difference between the sexes in seasonal growth (Mann-Whitney U -test: z = 0.58, P =
0.599). Seasonal growth rates were significantly higher in the wet season than in the dry
season (z = 3.05, P = 0.002).
Males and females exhibited an overall negative change in body mass during the dry
season, but there was a positive change in body mass by both sexes in the wet season
(Table 2.3 ) . Some males recorded a positive change in body mass in the dry season,
whereas most females exhibited a negative change in body mass in the dry season (Figure
2.7). Wet season values of change in body mass were significantly higher than dry season
25
.......... ...-' >. 8 rn · "0
E E .6
...._
<1) -<a '-
..c .4 -� 0 '-C) .2
ro c:: 0 en roo.o <1)
(/) 160
-..-'
>-<a 1.0
"0 C) I .8 o · 0' ...._
en .6 C/) ro E · .4 >-
"C 0 .2
..0 .� ').0
Q) Ol c:: -.2 ro
..c (.) -.4
160
(a) Males •
I •
•
• • e
• O O�<D 0 0
•
180 200 220 240 260 280
Snout to vent length (mm)
•
• •
c
180
(c) Males
•
•
•
0
200 220
" -�
;:( -
� -..1
� ,.. �0 o •
c.,...:: 0 'XC C) ,......,
c-::;• �6! 0 ...; '-'
:, ..... -'
240 260
Q
280
Snout to vent length (mm)
.......... ..... (b) Females ' >. <a .4
"0 •
E •
E .3 ...._
<D -ro '-
..c .2 -� • 0 '-C) .1 • ro c:: • 0 en • c
�
roo.o <1)
o cc -c:: •co
(/) 300 160 180 200 220 240
Snout to vent length (mm)
.......... ..-'>- (d) Females <a .0
"0 C) .8
� • 0 ...._ • en .6 • C/) ro
E .4 • >- •
"0 .2 0
..0 • .� 1.0
• -<' --,.., "
...; ,, <D '-' :-. C) c · �
�
� c:: -.2 ._,
<a • ..c
300 (.) ·.4 160 180 200 220 240
Snout to vent length (mm)
Figure 2.7. Seasonal growth rate (a,b) and percentage change in body mass (c,d) relative to
initial body length. Closed circles are wet season values and open circles are dry
season values.
26
Table 2 . 3 . Mean and standard error of seasonal growth rate as measured by changes in SVL (mm day-1) and change in body mass ( % g day-1) for male and female frillneck lizards in the wet and dry seasons. Numbers in parentheses are sample sizes.
Dry season Wet season
Males Growth rates 0.009 ± 0.003 0.108 ± 0.037
(mm day-1) (36) (14)
Body mass - 0.042 ± 0.015 0.176 ± 0.078
(% g day-1) (36) (14)
Females Growth rates 0.004 ± 0.003 0. 1 1 1 ± 0. 064
(mm day'1) (9) (10)
Body mass -0.058 ± 0.027 0.245 ± 0 . 1 14
(% g day-1) (9) (10)
27
values for both males and females using the mid-point SVL as the covariate, but this was
marginal (ANCOVA: males, F1•46= 3.92, P = 0.047; females, Fu6 = 4.55, P = 0.049).
Habitat use
Two methods were used to acquire data relating to habitat use and these methods have
important implications for the interpretation of these results. The ftrst method involved
locating frillneck lizards from a moving vehicle, and the second method involved relocating
frillneck lizards fitted with radiotransmitters. The first method of locating lizards may be
biased in three ways, and the bias is related to the fact that most lizards were perched on
vertical tree trunks: ( 1 ) different sizes of the tree trunks may alter the probability of
sighting an individual; (2) agamid lizards tend to move to the opposite side of a tree trunk
when approached or disturbed (Greer 1989), and this may influence the probability of
sighting; and (3) lizards perched on vertical trunks may be involved in foraging, social
interactions, and predation avoidance and/or detection (Stamps 1977 a, Shine 1 990).
Relocation of individuals using telemetry should not be influenced by these three factors.
Therefore, the data set has been divided into two groups, data from lizards with radio
transmitters (telemetered) and data from lizards without radio transmitters (non
telemetered).
Preliminary analysis indicated no differences between the sexes in the frequency
distribution of tree species used, therefore, males and females were combined in the
subsequent analyses. Sightings of lizards located on the ground were not included in the
statistical analysis. To determine if the data were biased by repeated observations, the
frequency distribution of trees species of five observations from each of six adult males
28
with transmitters, was compared to the single observations of tree species used by 30
individual adult males. Chi-square test revealed no difference in the frequency distribution
of tree species for repeated and single observations (X2 = 0.37, DF = 2, p = 0.832).
There was no difference in the frequency distribution of tree spectes occupied by
telemetered lizards between the dry and wet seasons (X2 = 8.87, DF = 7, P = 0.262).
Telemetered lizards frequently occupied Eucalyptus tetrodonta, with highest use of this tree
species occurring in the dry season (Table 2.4). During the wet season, telemetered lizards
increased their use of the Sand Palm (Livistona humilis) and dead trees, with a higher
proportion of lizards located on the ground. Compared to the random sample of tree
species, telemetered lizards used a significantly different distribution of tree species in both
dry and wet seasons (dry season, X2 = 63.52, DF = 7, P < 0.000 1 ; wet season, X2 = 26.87,
DF = 7, P = 0.0004). The telemetered lizards used a much higher proportion of Eucalyptus
tetrodonta than was available, and they under-used E. miniata (Table 2.4). The telemetered
lizards generally used the other tree species as would be expected from a random selection.
There was no difference in the frequency distribution of tree species used by non
telemetered lizards between the dry and wet seasons (X2 = 13.45, DF = 7, P = 0.062). The
frequency distribution of tree species used by these lizards during the dry season closely
reflected the availability of tree species (X2 = 6.55, DF = 7, P = 0.477). However, during
the wet season, they did not select trees according to availability (X2 = 44.55, DF = 7, P
< 0.000 1). Inspection of Table 2.4 reveals an under-usage of E. miniata, and a higher than
random use of the Sand Palm, Livistona humilis, by non-
29
Table 2.4 . The relative abundance (%) of tree species used by telernetered and nontelemetered frillneck lizards during the wet and dry seasons, and the relative abundance ( % ) of tree species available in the field as determined by a random walk technique.
Telernetered Non-telernetered Random
Dry Wet Dry Wet (%)
Tree species season season season season (%) (%) (%) ( %)
Eucalyptus tetrodonta 50.0 43.8 28.7 30.1 29.5
E. porrecta 1 1 .2 1 1 . 5 12.4 12.0 12 . 1
E. miniata 7.3 6.9 17.1 7.6 18.8
Erythrophleum chlorosrachys 1 1 .5 10.0 6.2 6.9 9.2
Terminal ia ferdinandiana 3.9 2.3 4.7 1.8 4.6
Livisrona humilis 3.9 8.5 5.4 1 1 .2 3.4
Planchonia careya 1 . 1 1 .5 2.3 0.7 0.5
Buchanania obvata 0.6 0.8 -- -- 0.5
Petalostigma pubescens 1 . 1 -- -- 0.4 0.7
Xanthostemon paradoxus 0.6 -- -- 1 .8 0.5
Eucalyptus tectifica 1 . 1 -- -- 0.4 0.2
E. bleeseri 0.8 -- - - 1 .4
E. clavigera -- 0.8 -- -- 0.2
E. confertiflora 0.3 -- -- -- --
Owenia vemicosa 0.3 -- -- -- 0.2
Acacia mimula 0.3 -- -- -- 1.8
Terminalia latipes -- -- -- 0.4 0.2
Terminalia grandiflora 0.3 -- -- -- --
Syzygium suborbiculare -- 1 .5 -- -- 0.5
Planchonella pohlmaniana -- 0.8 -- -- --
Melaleuca nervosa 0.8 -- -- -- --
Cochlospermum fraseri 0.8 -- -- -- --
Grevillea pteridifolia 0.3 -- -- -- --
dead tree 2.8 6.2 13.2 15.6 12. 1
other tree species -- -- -- -- 3.2
ground 1 .6 4.6 8.5 10.9 --
Total number of trees (n) 356 130 129 276 437
30
telemetered lizards during the wet season. There was a highly significant difference in the
frequency distribution of tree species occupied by telemetered lizards compared to non
telemetered lizards in the dry season, but not in the wet season (dry season, x2 = 44.88, DF
= 7, P < 0.000 1 ; wet season, X2 = 13.75, DF = 7, P = 0.056) (Table 2.4). The sampling
bias described in the previous section was evident in the analysis of structural habitat use.
Telemetered lizards were located on significantly larger trees than non-telemetered lizards
(tree height, t = 1 1 .06, DF = 737, P <0.000 1 ; trunk diameter, t = 14.69, DF = 737, P <
0.000 1) . Therefore, it was necessary to analyse the two groups separately.
Comparing the seasonal use of trees by telemetered lizards revealed that they used bigger
trees and were perched higher in the early and late dry seasons (Figures 2.8, 2.9, 2.10).
Trunk diameter was the only variable that was significantly different over the four seasonal
periods CANOVA: F3A41= 8.7 1 , P < 0.000 1) . Tukey's comparison of means test indicated
that the mean trunk diameter of the trees used in the early dry season was significantly
larger than the other three periods.
The height and trunk diameter of trees used by non-telemetered lizards remained constant
throughout the four seasonal periods (Figures 2.8, 2.9, 2 . 1 0). However, the perch heights
used by these lizards were significantly different CANOVA: F3.308= 9.09, P < 0.000 1 ) over
the four seasonal periods (Figure 2.10). Tukey's comparison of means test indicated that
the mean of the early dry season period was significantly lower than the late dry and early
wet season periods, but not significantly different from the late wet season period.
3 1
1 5
...-.... E .._ ....... ..c 0)
·- 1 2 Q) ..c Q) Q) '....... c: co 9 Q)
�
6
155
22
r- L --- --- -1--- 6 - - -r 65 1 1 17 85
44
late wet early dry late dry early wet
Seasons
Figure 2.8. The mean height of trees (m) used by frillneck lizards in four seasonal periods.
Closed circles are telemetered lizards, open circles are non-telemetered lizards,
nwnbers represent sample sizes. Error bars are one standard error.
32
- 25 E (.)
-..... .r:. 0> � 20 ..... U) ro Q) L-
.0 -ro 1 5 L-Q)
..... Q)
E ro
"'0 c: ro Q) :E
10
155
t-- - - f - - 4- - - Q 44 1 1 7 65
85
5 L---�----r-----.------,--late wet early dry late dry early wet
Seasons
Figure 2.9. The mean tnmk diameter (em) of trees used by frillneck lizards in four seasonal
periods. Closed circles are telemetered lizards, open circles are non-telemetered
lizards, numbers represent sample sizes. Error bars are one standard error.
33
..-... E ..._.. ...... £. C) Q)
£. ..c: (.) � Q) c.. c ro Q) �
1 2
1 0 8
6
4
2
155
22
44 Q- 1 1 7 --
- - -o-
206 60
65 85 A- - - o --
0 �--�------�------,--------r---late wet early dry late dry early wet
Seasons
Figure 2. 1 0. The mean perch height (m) of frillneck lizards in four seasonal periods. Closed
circles are telemetered lizards, open circles are non-telemetered lizards, numbers
represent sample sizes. Error bars are one standard error.
34
Seasonal activity index
The number of lizards captured or sighted per kilometre during censussing changed
substantially throughout the year (Figure 2 . 1 1) . This index showed that the largest number
of lizards were seen during the months of November through February, and the lowest
number of lizards were seen from June through August. The number of lizards sighted or
captured increased sharply between October and November (Figure 2. 1 1 ), and this period
coincides with the beginning of the frillneck lizard reproductive season (Shine and
Lambeck 1989). The pooling of monthly data into four seasonal periods produced unequal
variances between the four sample periods, therefore a Kruskal-Wallis one-way ANOVA
was used to test for differences among seasons. There was a significant difference among
the four seasons (z = 3 1 .73, P < 0.0001). Inspection of the activity index means indicated
that the two wet season periods were higher than the two dry season periods.
35
.6
X Q) .3 "'0 c � .2 >
·-__, u <( . 1
9 1 0
2
J F M A M J J A S 0 N D
Months
Figure 2. 1 1 . Monthly variation in number of lizards sighted or captured per kilometre driven
during routine censussing of sites. Numbers are the number of censuses each month,
error bars are one standard error.
36
DISCUSSION
Frillneck lizards undergo seasonal changes with respect to diet, condition, growth, habitat
use and activity. The dry season is characterised by a decrease in the activity of frillneck
lizards, selection of large Eucalyptus trees when perched in the canopy, and a relatively
small amount of food in their stomachs. This reduction in food is reflected in reduced
growth rates and a small decrease in body mass, although general body condition remains
relatively stable. The lizards continue to feed on a diverse array of arthropods despite
overall low prey abundance. Termites, centipedes and ants are common prey items. The
wet season is characterised by an increase in activity of the population, selection of shorter
trees with small diameters, and an increased amount of food in their stomachs. This
increase in activity coincides with four ecologically significant events: ( 1 ) an increase in
ambient temperatures; (2) the onset of rainfall; (3) an increase in food availability; and (4)
the onset of the reproductive period. The relative importance of these four factors is
unclear in determining the behaviour of C. kingii, but they are probably all important.
The previous dietary results of Shine and Lam beck ( 1989) are consistent with this study,
particularly with respect to wet season data. Both studies found a diverse diet with a high
relative abundance of isoptera, Iepidoptera and hymenoptera. One notable difference
between the two studies of diet is the low proportion of centipedes reported by Shine and
Lambeck ( 1 989).
One of the most interesting aspects of the prey taken by Chlamydosaurus is the high
incidence of the harvester termite, Drepanotermes, in the diet throughout the year.
37
Drepanotermes is a widespread endemic genus (of at least 23 species) which inhabits arid
and tropical regions of Australia. They differ from other harvester termites by foraging in
the day and at night, whereas other harvester termites forage only at night (Watson and
Perry 198 1 ). Over 1 9 species of Drepanotermes occur in the arid regions of Western
Australia, with between four and eight species occurring in the Top End of the Northern
Territory (Watson 1982). The effect of seasonal conctitions in the wet-dry tropics on the
foraging behaviour of harvester termites is unclear, because sweep-netting from this study
ctid not sample termites. Foraging and reproduction in Drepanotermes are restricted to
summer months in arid and temperate habitats (Watson 1974, Watson and Perry 1981, Park
et a/. 1993). The presence of large quantities of Drepanotermes in the stomach contents
of Ch/amydosaurus in the dry season, suggests these harvester termites are active
throughout the dry season months in the study area. Dry grass is the preferred food item
of Drepanotermes (Watson and Perry 1981), and dry grass (Sorghum spp.) is more
abundant during the dry season in northern Australia.
Termites are an important food source for many species of lizards in arid environments
(Pianka 1 986, Morton and James 1988, James 1991b, Abensperg-Traun 1994). The
presence of termites in the diet of lizards has been related to foraging mode in arid habitats
(Huey and Pianka 198 1 ) . Lizards that are primarily sedentary in locating prey or "sit-and
wait" foragers (in arid habitats) tend to encounter and eat fairly mobile prey (e.g. ants,
centipedes), whereas more actively foraging lizards consume less active prey (e.g. termites,
caterpillars) (Huey and Pianka 1981). There is some difficulty in categorising invertebrates
into these functional groups, but they have been generally accepted in previous research.
38
Data from lizards in tropical Brazilian forests support this general hypothesis, with widely
foraging lizards consuming a greater proportion of termites (less mobile prey) than other
less actively foraging lizards (Magnusson et al. 1985). Table 2.5 summarises studies of
tropical lizards with respect to foraging mode and termite prey in tropical environments.
The relative volume of prey were not provided in a number of studies, therefore only
relative abundance is presented. The proportion of termites in the diets of six species of
tropical "sit-and-wait" lizards (excluding Chlamydosaurus) in open and closed forests was
neglible, whereas the proportion of ants was generally high. In contrast, the diets of active
foraging lizards in tropical habitats included a substantial proportion of termite prey, and
relatively fewer ant prey. This relationship supports the foraging strategy hypothesis of
Huey and Pianka ( 1981 ). The saxicoline Tropidurus group displays a high numbers of both
social insect prey groups. Comparisons of this group are problematic as they may use a
range of foraging strategies, and they also consume some plant material. The presence of
a large proportion of both termites and ants in the diet of Chlamydosaurus is clearly
distinct Considering the almost exclusive "sit-and-wait" foraging strategy used by
Chlamydosaurus (Shine and Lambeck 1989), they appear to be an exception to the
generalisation (Huey and Pianka 1981). However the presence of other mobile prey
(orthoptera and chilopoda) in the diet of Chlamydosaurus, broadly supports the pattern of
a sedentary predator consuming mobile prey.
Much of this hypothesis is based on the assumption that the spatial distribution of termites
is unpredictable (Wilson and Clark 1977 as cited in Huey and Pianka 198 1) . A possible
explanation for the relationship between frillneck lizards and harvester termites, is that
Drepanotermes have a more even spatial distribution or higher density than is generally
39
Table 2.5. A summary of tropical lizard's foraging strategy, habitat, and the relative abundance of ants and termites in their diets.
Species Climate Foraging Habitat type Diurnal? Ants Termites Reference
mode' ( % ) (%)
Chlamydosaurus kingii wet-dry sw open forest yes 1 8 . 1 74.6 This study
C. kingii wet-dry sw open forest yes 26.5 56.2 Shine and Lambeck 1989
Anolis auratus wet-dry sw open forest yes 75.0 0 Magnusson et al. 1985
A . opalinus wet-dry sw open forest yes 69.4 0 Floyd and Jenssen 1983
A. cupreus wet-dry SW open forest yes 34.3 0 Fleming and Hooker 1975
A . aeneus wet-dry SW closed forest yes 3 1 . 5 0 Stamps et al. 1981
A . oculatus wet sw closed forest yes 46.8 5 .2 Bullock et al. 1993
Corytophanes cristatus wet sw closed forest yes 0 0 Andrews 1979 0 -.:t
Plica plica wet-dry sw closed forest yes 6 1 . 1 0 Vitt l991b
Uranoscodon superciliosum wet-dry sw closed forest both 24.3 0 Howland et al. 1990
Tropidurus spp (4 species) wet-dry ? open forest yes 42.3 44.7 Vitt 1 993
Kentropyx calcarata wet-dry WF open forest yes 2 .8 3 . 1 Vitt 1 99 1 a
K. striatus wet-dry WF open forest yes 45.0 20.0 Magnusson et al. 1 985
Ameiva ameiva wet-dry WF open forest yes 5.0 75.0 Magnusson et al. 1985
Cnemidophorus lemniscatus wet-dry WF open forest yes 25.0 60.0 Magnusson et al. 1985
C. deppii wet-dry WF coastal yes 2 .3 86.6 Vitt et al. 1993
Mabuya bistriata wet-dry WF closed forest yes 9.0 45 . 1 Vitt and Blackburn 1 99 1
a. foraging mode either SW = sit-and-wait or WF = widely foraging.
considered to be the case for termites. The density and spatial distribution of
Drepanotermes in tropical open forests are unknown. Density estimates of Drepanotermes
in arid habitats may be as high as 200 mounds ha·1 (Watson and Perry 1981 ) , although no
estimates are available for Kapalga. A high density of termites would increase their
predicability and availability to both "active" and "sit-and-wait" foragers. The above ground
activity during day by harvester termites allows Ch/amydosaurus to access a large,
relatively constant food resource. This may be an important factor in the diet of
ChlamydosG;urus, especially during the dry season when other food sources are relatively
low. This food supply may possibly be available to other "sit-and-wait" insectivorous
lizards, as well as actively foraging insectivorous lizards.
A reduction in the volume of food taken during dry conditions is a commonally observed
pattern for lizards inhabiting arid and temperate seasonal environments, and it is a direct
response to decreased food availability (Ballinger and Ballinger 1979, Rose 1 98 1 , Stamps
and Tanaka 198 1 , James 1991b). Unfortunately, information on the total volume of
stomach contents is available from only two dietary studies of tropical lizards listed in
Table 2.5. Bullock et a/. ( 1993) reported no seasonal change in number of items or total
volume of stomach contents for Anolis oculatus, despite large differences in food
availability. Another tropical iguanid, Anolis oplinus, showed no change in the volume of
stomach contents between wet and dry seasons (Floyd and Jenssen 1 983). Reduced growth
during periods of low food and water availability has been well documented in lizards
(Stamps 1977b, Dunham 1 978, Ballinger and Congdon 1980, Stamps and Tanaka 1 98 1 ,
Andrews 1982), and Ch/amydosaurus follows this pattern. Feeding continues throughout
the dry season, but the volume of food taken is apparently not sufficient to support rapid
4 1
growth. The reduced field metabolic rate during the dry season (Christian and Green 1994 ), suggests that the lizards are generally conserving energy. A small decrease in body mass
(mean = 1 .35% per month) of the lizards reflects this.
Male frillneck lizards were able to maintain a relatively constant level of body condition
throughout the dry season. However, the body condition of males decreased during the
early wet season, which is the beginning of the reproductive season for this species. Even
though there is a marked reduction in food availability during the dry season, a decrease
in activity levels and the reduction in field metabolic rate (Christian and Green 1 994)
enables males to minimise the loss of body condition during this period of limited food
resources. This seasonal pattern in body condition is consistent with males of other tropical
lizard species (Fleming and Hooker 1975, Floyd and Jenssen 1983, Howland et a!. 1990).
Female Chlamydosaurus exhibit a more variable pattern of body condition across the
seasons, with low body condition in the late wet season and the late dry season.
Expenditure of energy for reproduction may explain the drop in body condition in the late
wet season because this corresponds with the period of oviposition. The late dry season is
the period with the lowest availability of prey (Table 2.2, Churchill 1994 ), and is the
season prior to the reproductive season. However, it is not clear why female body condition
is lowest at this time but males is lowest in the early wet season (three months later),
especially with a similar volume of food in their stomachs. This may be related to the
energy used by males in territorial defense and mate acquisition at this time, whereas
females may spend this time feeding.
42
Trees are an important component of the habitat used by C. kingii. Over 95% of all lizards
in this study were located in trees, and this agrees with previous observations (Shine and
Lambeck 1989). The use of structural habitat by frillneck lizards changes with rainfall,
food availability, activity and reproductive season. The way habitat data were collected
should be considered for the interpretation of the data. If only one of these sampling
methods was used (telemetry or vehicle) then only one conclusion would be possible. If
only non-telemetered lizards were used to study habitat use then the conclusion would be
that frillneck lizards randomly selected the tree species available, and the size of trees
selected remains constant throughout the year. If only telemetered lizards were used, then
the conclusion would have been that frillneck lizards show a strong preference for
Eucalyptus tetrodonta and a seasonal change in size of trees selected (trunk diameter and
tree height).
Therefore, it is important to consider the behaviour of lizards with respect to the reasons
they perch on vertical tree trunks. The perching by lizards on vertical tree trunks has been
related to feeding and social interaction (Scott et a/. 1976, Stamps 1 977a, Shine 1990). It
is suggested here that frillneck lizards that were seen from the vehicle were engaged in
either foraging or social behaviour, and that this behaviour corresponds to the use of
relatively small trees at all times of the year. This behaviour on low perches takes place
on tree species in proportion to their abundance. Frillneck lizards fitted with telemetry
devices are generally perched higher in trees, and their selection of tree size changes
significantly throughout the year. This seasonal change is related to a general decrease in
activity, and the lizards apparently use the large trees as a dry season refuge (Christian and
Green 1994). This is also reflected in the behaviour of some telemetered lizards that
43
remained in the same tree for prolonged periods (up to three months). During the wet
season, however, frillneck lizards regularly changed trees (Shine and Lambeck 1989, pers.
obs.).
Summary
In summary, frillneck lizards show considerable seasonal change in their behaviour and
ecological relationships in the wet-dry tropical environment. No specific environmental
variable was identified as being responsible for these changes because of the inter
dependence of these environmental variables. Frillneck lizards continue to feed on a diverse
range of invertebrates during low food availability in the dry season. The presence of
termites in the diet of frillneck lizards indicates a fundamental difference from other
tropical "sit-and-wait" lizards. It also offer a constant food supply in the dry season. The
volume of stomach contents is reduced in the dry season, which in turn reduces the growth
of frillneck lizards. Lower levels of activity in the dry season coincide with lizards
selecting large Eucalyptus trees, in which they become very inconspicuous until the
beginning of the reproductive season in October. Male lizards held their body condition
during the dry season to a greater extent than females. Differences in reproductive roles
of the two sexes may be responsible for seasonal differences in body condition.
44
Chapter 3 The short-term and longer-term effects of annual fire on the behaviour,
diet, growth, and habitat use of the frillneck lizard, Chlamydosaurus kingii.
INTRODUCTION
Fire is an important environmental factor for many vertebrate communities within Australia
(e.g. Newsome et al. 1975, Fox 1982, Braithwaite 1987, Woinarski 1990) and elsewhere
(e.g. Gillon 1983, Clark and Kaufman 1990, Mushinsky 1992). Fire creates a mosaic of
habitats within environments, and this may be crucial in the maintenance of species
diversity.
Previous studies of lizards and fire have documented changes in species abundance and
community composition related to the seral changes in the habitat structure after fire (Lee
1 974, Lilywhite and North 1974, Barbault 1977 as cited in Gillon 1983, Simovich 1979,
Fyfe 1980, Means and Campbell 1981, Patterson 1984, Caughley 1985, Mushinsky 1985,
Bamford 1986, Braithwaite 1987, Woinarski 1989, Lunney et at. 1991, Masters 1991,
Mushinsky 1 992, Trainor and Woinarski 1 994). Changes to the habitat structure may alter
the relationship between the lizards and their thermal environment, food resources and
predators.
In contrast, relatively few studies have investigated the short or longer-term effect of fire
on the ecology of individual lizards or a single species of lizard (Kahn 1 960, Lilywhite and
North 1974, Bamford 1986, Mushinsky 1 992). The response to fire of individual species
shows wide variation in this literature, which possibly reflects the diverse life histories of
45
these lizard species. Additional information is needed about the relationship of individual
lizard species and flre to make management and conservation decisions.
The majority of research on lizards and fire has been done in temperate and arid regions
where fire is generally of low frequency. Important differences in the effects of frre on
lizard communities exists between tropical and temperate environments based on the
differences in the frequency of fire (Braithwaite 1 987). Habitat succession after fire is less
important to lizard communities in tropical savannas because the higher frequency of frre
does not allow habitat succession to occur. Rather, it is the time of year and related
intensity of the fire that are important in determining composition and abundance in lizard
communities (Braithwaite 1987). Trainor and Woinarski ( 1 994) support this, although they
suggest that moisture availability is a more dominant factor in determining the composition
of lizard communities in tropical savannas.
Fires occur on an annual or biennial basis in open forest and woodlands of northern
Australia (Braithwaite and Estbergs 1985). There is evidence that, subsequent to settlement
of Europeans in northern Australia, the fire regime has changed from a relatively high
frequency of low intensity burns early in the dry season to one of more intense burns later
in the dry season (Haynes 1985, Braithwaite and Estbergs 1985, Press 1988). This
alteration in timing and intensity of frres in northern Australia increases the need for
ecologists and land managers to be able to understand the effects of different fire regimes
in this environment.
The distribution of Ch/amydosaurus kingii extends throughout open forests and woodlands
46
of northern Australia (Cogger 1992). The general ecology of this species was reported by
Shine and Lam beck ( 1989). During the dry season frillneck lizards decrease their field
metabolic rate, water turnover and body temperatures (Christian and Green 1994, Christian
and Bedford 1995). During the dry season C. kingii have reduced activity and feeding rates,
and they select larger Eucalyptus trees than during other seasons (Chapter 2: Diet and
Seasonal activity). This period of relative inactivity coincides with the majority of fues in
the savannas of northern Australia.
This chapter examines two aspects of the effect of fire on the ecology of Chlamydosaurus
kingii: ( 1 ) the short-term effect of two different fire treatments on mortality, behaviour, diet
and post-fire habitat selection; and (2) the longer-term effects of three different fire regimes
on habitat selection, diet, body condition and seasonal growth.
METHODS
Sites
For a full description of the site and climate see Chapter 2 (Methods: Site).
Fire treatments
Prescribed fues were lit by CSIRO's Division of Wildlife and Ecology at Kapalga
Research Station (Kakadu National Park), as part of a landscape-scale, replicated fire
experiment. Three different fire regimes were used for this experiment that represent fue
regimes experienced in open forests and woodlands in northern Australia. The fire
treatments were:
47
Early dry season fires. These fires are lit annually at the beginning of the dry season
(May/June), approximately three months after cessation of monsoonal rains. They are
characterised by low intensity, low flame height ( 1 -2 m), and a slow rate of spread (< 0.5
m sec·1). They invariably leave substantial areas (30-70lk) of unburnt ground vegetation,
and seldom scorch the upper tree canopy. The fire treatment had been applied annually
to one study area (Early fire, Figure 3 . 1 ) since 1990.
Late d1y season fires. These fires are lit annually at the end of the dry season (September),
approximately six months after cessation of monsoonal rains. They are characterised by
high intensity, high flame height (2-4 m), and a faster rate of spread (> 1 m sec·1). All
ground vegetation is usually consumed during the fire, and a large proportion of the tree
canopy (> 80lk) is scorched. The increased intensity of these fires, compared to the early
dry season fLies, is due to higher fuel loads plus increased wind speeds, and lower relative
humidity. The treatment had been applied annually to one study site (Late fire, Figure 3 . 1 )
since 1990.
Unbumt. The treatment involved the total exclusion of fire, which had been applied to one
study area (Unburnt, Figure 3 . 1 ) since 1988.
The large amount of work and time involved in the collection of data prevented replication
of treatments. Also, the large area of sites (400-500 ha) required to sample a sufficient
number of lizards in each fLie treatment made replication unrealistic.
48
-
Floodplain
N
0 5 km
Figure 3 . 1 . Location of three penn anent fire treatment sites within Kapalga Research Station.
The shaded areas represent each site
49
Sampling
Frillneck lizards were monitored using both telemetry and mark-recapture methods, which
are described in Chapter 2 (Methods: Sampling). Both of these sampling methods provided
data on behaviour, habitat use, food availability, diet and body condition of the three
populations. The intensity of individual fires (kW m·1) were measured by the CSIRO.
Short-term effects of fire
Individual lizards (fitted with radio transmitters) were located in trees immediately before
a prescribed fire was ignited. The trees were marked, and the tree height (m), trunk
diameter at breast height (em), and perch height (m) of the lizard was recorded. Lizards
were relocated immediately after the fire front had passed in order to determine mortality
or subsequent movements. Changes in the location of lizards during a fue were recorded.
Stomach contents of lizards were obtained by stomach flushing large lizards (SVL > 150
mm) within two hours of capture (Chapter 2: Methods). This was done one week before
and one week after fires, allowing a minimum of two days after fires to minimise the
overlap with pre-fue stomach contents. Lizards that were stomach flushed before fues were
not re-sampled after fires.
Data concerning post-fire habitat selection by lizards were collected during the fust year
of this study ( 1991 ), prior to the establishment of permanent study sites. Telemetry was
used to observe lizards over a large area, to determine whether they preferred or avoided
burnt or unburnt habitat. Lizards were captured at the boundaries of fire treatment sites
before prescribed fires were lit, so that after fires there was both burnt and unburnt habitat
50
available nearby. They were monitored immediately before fires and at regular intervals
up to two weeks after fires.
Longer-tenn effects of fire
An important objective of this study was to determine whether the use of the structural
habitat (occupancy of trees) by frillneck lizards was influenced by a particular factor (or
combination of factors) of the structural habitat, and whether different fire regimes
influenced this relationship. This was done by comparing the structural characteristics of
the trees (and surrounding ground vegetation) occupied by frillneck lizards against a
randomly selected sample of trees and surrounding vegetation within the same habitat.
Lizards were assumed to be absent from this randomly selected sample.
Data on structural habitat use by frillneck lizards were collected specifically during dry
season months (prior to annual fires in early dry and late dry season fire sites) for two
reasons: ( 1 ) the habitat use of telemetered lizards changes between wet and dry seasons
with regard to height and diameter of trees selected (Chapter 2: Habitat use); and (2) the
habitat structure undergoes dramatic change after fire, and again during the wet season.
Therefore, it was necessary to collect data during the dry season (prior to fire treatments)
to minimise the influence of these factors before comparisons of the different fire regimes
could be made.
Data from trees occupied by frillneck lizards fitted with telemetry devices were used in the
analysis of structural habitat because there was as a sampling bias in the mark-recapture
method (Chapter 2: Habitat use). Tl}e random sample of trees was selected using a random
5 1
walk method (Goldsmith and Harrison 1976). A minimum distance of 30 m was set
between randomly selected trees to increase the independence of each sample. The
following structural habitat variables of trees were recorded:
Tree height: Tree height (m) was measured using a clinometer.
Diameter: The diameter (em) of each tree trunk was measured at breast height using a
calibrated measuring tape. For trees with more than one trunk, a mean of all trunks was
taken.
Tree canopy: The amount of canopy cover of individual trees was recorded using a five
-point ordinal scale ( 1 , l -5%; 2, 6-25%; 3, 26-50%; 4, 5 1 -75%; 5, 76-100%), that was
estimated visually.
The following structural habitat variables were collected within a three metre radius from
each tree trunk:
Ground vegetation density: The ground vegetation density was recorded in circular quadrats
(0.4 m2 in area). Within each quadrat, the total number of contacts of ground vegetation
against a piece of string rotated horizontally were measured at four heights (25, 50, 100,
150 em). Three quadrats were collected per tree, and an average of number of hits at each
height was taken. Means were converted to a density (hits m2) at each height.
Litter cover: The litter cover was measured by the total number of leaves pierced by a steel
pin in 10 sample points per tree.
Bare ground: The percentage of bare ground was estimated visually within a three metre
radius of the tree.
52
Data on the selection of tree species by frillneck lizards were collected separately from
structural habitat data. Tree species was recorded at all captures and sightings of lizards
throughout both wet and dry seasons at each site. Sampling of tree species available to
lizards was collected at each site using a random walk method (Goldsmith and Harrison
1976). This is described in Chapter 2 (Methods: Sampling).
Stomach samples were collected from large lizards (SVL > 150 mm) captured within each
site. Stomach contents of lizards were collected by stomach flushing and later sorted and
total volume measured (Chapter 2 : Methods). Regular sampling was done from April 1992
to April 1994.
Analyses
Short-term effects of fires
Data from the three fires per fire treatment were combined for analyses. Student's t-test
was used to analyse changes before and after fires with respect to total volume, number
of items in stomach contents, and the height of trees used before and after fire. Difference
between early and late fire behavioural responses during fire were analysed using
Kolmogorov-Smirnov two sample test.
Longer-term effects of fire
Six different measures were used to analyse the short and longer term effects of fire on the
stomach contents of frillneck lizards: ( l ) the total number of items; (2) the total volume
(rnl); (3) the relative abundance (%) of each prey taxa; (4) the relative volume (%) of each
prey taxa; (5) the occurrence (%) of one or more prey taxa in stomach samples; and (6)
53
the number of prey taxa and size classes present in each stomach sample. Stomach samples
from the dry and wet seasons were analysed separately for longer-term variation among fire
regimes. A single factor analysis of variance (ANOV A) was done to test for differences
in total volume among sites, for wet and dry seasons separately. A non-parametric ANOV A
(Kruskal-Wallis) was used to test for differences in the frequency distribution of prey size
classes and prey taxa among fire treatments.
Logistic regression analysis was used to determine the factors that affected the occupancy
of trees by frillneck lizards during the dry season. This technique uses a logistic probability
curve through binary data (occupied trees versus unoccupied trees). The logistic curve has
the form
P(y= l ) = EXP(G)/(1 + EXP(G)]
where P(y= 1 ) is the probability that an individual will occupy a certain tree; G is
analogous to a standard regression equation and is
where A is a constant; xil• xiN = the first and ith independent terms in the model; Bl, BN
= the coefficients for the first and nth terms of the model; and i = 1 , 2, . . . . . .N (individual
trees).
54
The terms of the logistic model were estimated using maximum likelihood, termed ' scaled
deviance' in this analysis. Scaled deviance is analogous to the F ratio in standard
regression analysis, but has an approximately chi-square distribution. Degrees of freedom
are equal to the difference in the number of degrees of freedom from an original null
model, when each term is added to the model (McCullagh and Neider 1983 ) . Terms and
interactions were added to the model using a forward selection method where all single
terms are added to an original null model individually, with the term producing the greatest
significant decrease in scaled deviance being selected into the model. This process was
continued with each set of remaining independent terms until no significant decrease was
achieved by any of the remaining terms. Quadratic terms (XixXi) were tested with each
independent term to determine the presence and significance of non-linear relationships
within the model. Interaction terms (denoted by multiplication sign between two terms)
were then tested in the same manner, after the analysis of single terms.
A final model of occupancy of a tree was evaluated using two methods: ( 1 ) testing the
significance of each of the accepted terms, by deleting each term individually from the full
model, with non significant terms being rejected from the model; and (2) examination of
the relationship between coefficient values and standard errors of accepted terms to test the
significance of approximate t values (Nicholls 1985 ).
Selectivity of tree species by frillneck lizards was calculated using Strauss's ( 1 979)
electivity index. This index is calculated for each tree species:
L = ri - Pi
where ri is the relative abundance of each tree species used by frillneck lizards in both wet
55
and dry seasons and Pi is the relative abundance of the same trees species in each site as
determined using the random walk method.
Differences among fire treatment sites in lizards' body condition was determined by
ANOVA of mean residuals from a linear regression of log-body mass with log-SVL (James
1991 a). Samples were pooled into wet and dry seasons.
All means are presented with one standard error unless stated otherwise.
RESULTS
Short-term effects of fire
A total of 17 frillneck lizards were monitored using telemetry during three early dry season
ftres. The intensity of the fires at ground level were approximately 5000, 1000 and 800 kW
m·' for 1991 , 1992 and 1993 respectively (Williams et a/. unpublished data). All lizards
were relocated after the fires, and no direct mortality was .recorded during early dry season
fires. A possible indirect mortality may have occurred after one animal was scorched
during a ftre, losing at least 1 2 toes and therefore being unable to climb. This would reduce
its chances of survival dramatically, but the fate of the animal was not determined. During
early dry season fires lizards tended to remain in the trees they occupied before fire (59%),
with a smaller proportion changing trees (35%), and one lizard (6%) sheltered in a disused
hollow termite mound. The height of trees used by lizards immediately before fire was not
significantly different (paired t-test: t = 1.06, OF = 5, P = 0.34) compared to trees to which
56
lizards moved during a fire.
A total of 24 frillneck lizards were monitored using telemetry during three late dry season
fires. The intensity of the fires at ground level were approximately 10,000, 9000 and 8000
kW m·• for 1991, 1992 and 1993 respectively (Williams et a!., unpublished data). All
lizards were relocated after the fires. Six were killed as a direct result of the fires, and
another lizard died two weeks after a fire because of the severe scorching it received while
perched in the tree canopy. This represents 29% mortality during late dry season fires.
Compared to the early dry season fires, lizards exposed to high intensity late dry season
fires were less inclined to remain in the same tree during a fire ( 1 6% ) , although a similar
proportion changed trees (25% ), and most notably seven lizards (30%) found shelter in
hollow termite mounds on the ground. Those lizards that changed trees during a late dry
season frre selected significantly taller trees (paired t-test: t = 3.79, DF = 1 1 , P = 0.0 1 3)
compared to the trees they occupied before the fire. The behavioural responses of frillneck
lizards to late dry season fires differed significantly from their responses to early dry
season fires (Kolmogrov-Smirnov two-sample test: D = 0.53, P = 0.008).
The stomach contents of frillneck lizards contained a mean of 9.5 ± 4.23 (n = 10) items
during the week before early dry season fires, and this increased to 16. 1 3 ± 4.03 (n = 15)
items one week after frres, but this increase was not significant (unpaired t-test: t = 1 .0 1 ,
DF = 24, P = 0.283 ) . The mean total volume of stomach contents increased from 2.08 ±
0.94 ml before frre to 3 . 1 0 ± 0.67 ml after fire, but this increase was not significant (t =
0.9 1 , DF = 24. P = 0.37 1 ). Figure 3.2 illustrates the frequency distribution for the number
of insect orders and number of prey size classes present in each stomach, one week before
57
and one week after fire. Stomach contents after fire tended to contain a greater number of
prey orders and prey size classes. However, only the number of size classes was
significantly different for before and after fire comparisons (Mann-Whitney U-test: z =
2.58. p = 0.035 ).
Hymenoptera was the most commonly taken prey taxon before and after the early dry
season fires (Figure 3.3). The relative abundance of hymenoptera decreased after fires,
whereas orthoptera, hemiptera and coleoptera showed a small increase in relative
abundance (Figure 3.3). Although hymenoptera were numerically abundant, the relative
volume in the stomach contents of lizards was small. The relative volume of blattodea,
chilopoda and aranea decreased after fires, but the relative volume of orthoptera, hemiptera,
coleoptera and Iepidoptera increased (Figure 3.3). The distribution of the relative abundance
of prey taxa did not change significantly after fires (Kolmogorov-Smimov two sample test:
D = 0.08, P = 0.805). However, the distribution of the relative volume of prey taxa was
significantly different after fires (D = 0.5 1 , P < 0.000 1 ).
A total of 53 stomach contents were collected for the analyses of the short-term effects of
late dry season fire, and they contained a mean of 59. 10 ± 2 1 .05 (n = 20) items before
fires, and this decreased marginally to 57.00 ± 10.94 (n = 33) after fires. This decrease was
not significantly different (unpaired t-test: t = 0.07, DF = 52, P = 0.93). The mean
58
� 5 c.. E C0 4 (J)
..c () C0 3 E 0 .... (J) 2 -0 � � 1 E ::J z o
0 1 2 3 4 5 Number of prey size classes
(J) <1> 8 c.. E co (J) 6
..c () co E 0 4 .... (J)
-0 � <1> 2
..0 E
II ::J Z o
0 2 3 4 5 6 7 8
Number of invertebrate orders
Figure 3.2. Frequency distribution of the number of invertebrate orders and prey size classes
in the stomach contents of frillneck lizards, one week before and one week after early
dry season fire. Open bars represent before fire and closed bars represent after fire.
59
-
:::R e._. 80
Q) u c: ro 60
"'0 c ::::J
.c 40 ro
Q) >
20 ..... ro
Q) 0:: 0
60 -
:::R 0 -
Q) 45
E ::::J 0
30 >
Q) >
..... 1 5 ro
Q) 0::
0
ci ..!!!
ci �
e ci ci [ c ui c � 0 - c :E 0 Cll .. 0 .. .. ... Cll 0 ..J iii .. "0 .s::. ... 0 0 X X :E 0 0.. C(
Invertebrate orders
e € Cll 0 X
....: 'ci 0 ·-0 0 ci [ Cll ..J X
c ui c 7;; c 0 .. .. iii .. "0 .s::. ... :E 0 c. C(
I nvertebrate orders :E 0
... Cll .s::. 0
... Cll .s::. 0
Figure 3 .3 . Relative abundance and relative volume of prey taxa in stomach contents, one
week before and one week after early dry season fire. Open bars represent before fire
and closed bars represent after fire. Abbreviations for prey taxa are: I so.- Isoptera;
Orth. - Orthoptera; Hem. - Hemiptera; Col. - Coleoptera; Dip. - Diptera; Lep. -
Lepidoptera; Hym. -Hymenoptera; Blat. - Blattodea; Mant. - Mantodea; Odon. -
Odonata; Phas. - Phasmotodea; Aran. - Aranea; Chi/. - Chilopoda.
60
total volume increased from 3.28 ± 0. 94 ml before fires, to 6.01 ± 0.84 ml after fires, and
this increase was significant (t = 2.08, OF = 52, P = 0.042). The number of invertebrate
orders and the number of size classes present in stomach contents increased after fue
(Figure 3.4). Stomach contents collected after late dry season fires contain a significantly
greater number of prey size classes (Mann-Whitney U-test: z = 2.85, P = 0.04). This result
helps explains how the total volume differed significantly between the two periods, but the
number of items did not. Lizards consume a greater range of prey size classes after fires,
which increases the total volume of stomach contents. There was also a significant increase
in the number of prey taxa in stomach samples after late dry season fires (Figure 3.4, z =
3.34, p < 0.00 l ).
Isoptera were the most commonly taken prey taxa before late dry season fues, accounting
for approximately 65% of relative abundance, and 30% of relative volume (Figure 3.5).
This was reduced considerably after fires, when isoptera accounted for 23% of relative
abundance, and only 6.5% of relative volume. Hymenoptera, however, increased in relative
abundance and relative volume after the late dry season fires (Figure 3.5). Orthoptera,
hemiptera, coleoptera, and chilopoda also increased in relative abundance and relative
volume immediately following late dry season fires (Figure 3.5). Both the distribution of
the relative volume and relative abundance of prey taxa were significantly different after
late dry season fires (Kolmogorov-Smirnov two sample test: relative volume, D = 0.22, P
= 0.022; relative abundance, D = 0.41, P < 0.000 1) .
61
en Q) 14 a. � 12 en
..c 10 (.) m E 8 0 -en 6 .._ 0 � 4 Q) .c E 2 :::s
z 0 ....... -+---'--
en Q) 10 a. E m en 8
..c (.)
E 6 .9 en .._ 4 0 � Q) .c 2 E :::s
z 0 n 0
0 2 3 4 5
Number of prey size classes
,-
I
�
2 3 4 5 6 I
7 8
Number of invertebrate orders
Figure 3.4. Frequency distribution of the number of invertebrate orders and prey size classes
in the stomach contents of frillneck lizards, one week before and one week after late
dry season fire. Open bars represent before fire and closed bars represent after fire.
62
-:::R 80 0 .._
Q) g 60 ro
"'C c: :l 40
..0 ro
Q) > 20
....... ro Q) 0::
-
:::R 0 .._
Q) ' E :l
0 >
Q) >
....... ro Q) 0::
0
60
45
30
1 5
0
0 .!!
0 !!
ci. c IIi c ... � E 0 ci. E i;j c :E Ql 0 Ql 0 � � .s::. 0 Ql (J ..1 >- iii � "C .s::. ... (J 5 :z: :z: � 0 c. �
I nvertebrate orders
ci. ci. c ... � E 0 E i;j c c IIi :E Ql 0 Ql 0 � � .s::. 0 Ql (J ..1 >- iii � "C .s::. ... (J 5 :z: :z: � 0 c. �
I nvertebrate orders
Figure 3 . 5 . Relative abundance and relative volume of prey taxa in stomach contents, one
week before and one week after late dry season fire. Open bars represent before fire
and closed bars represent after fire. Abbreviations of invertebrate groups follow Figure
3 . 3 .
63
The data presented in Table 3.1 summarises the response by frillneck lizards for post-fire
habitat selection two weeks after early and late dry season fires. Frillneck lizards either
remained in freshly burnt areas or moved into burnt areas from the adjacent unburnt areas
after early dry season fires. Only one individual (of 2 1 observed) left a recently burnt area,
while two remained in the unburnt habitat next to a burnt area. The movements following
late dry season fires are more variable, with some lizards leaving burnt areas, and some
moving into the freshly burnt areas. However, most of the areas adjacent to the late fire
plots had been burnt three months previously for early dry season prescribed fires, so there
was less distinction between areas because the individuals outside late fire areas were
already in burnt habitat. There was a significant difference in the distribution of responses
to the two fue treatments (Kolmogorov-Smirnov two sample test: D = 0.32, P < 0.000 1 ).
Longer-term effects of fire
Data on habitat structure were collected from 177 trees occupied by frillneck lizards (with
radio transmitters) during dry season months. Data from a further 104 randomly selected
trees (unoccupied) were collected concurrently. Table 3.2 summarises the data for each of
the structural habitat variables for both occupied and unoccupied trees at each site.
Logistic regression analysis identified four structural habitat variables that influenced the
occupancy of trees by frillneck lizards during the dry season (Table 3.3). The amount of
tree canopy cover, and the density of the ground vegetation at (25 em above the ground)
were the two most significant terms present in the regression model. Both diameter and
height of trees were significant terms, although they were only a minor influence on the
64
Table 3 . 1 . Post-flre selection of habitat by telemetered frillneck lizards. All lizards were monitored adjacent to burnt or unburnt habitat after the early and late dry season fires during 1991 .
Remain in Move out of Remain in Move into Total Fire burnt area burnt area unburnt area burnt area treatment
No. % No. % No. % No. % No.
Early dry 12 57 1 5 2 10 6 28 21
season fire
Late dry 3 25 4 33 3 25 2 17 12
season fue
Total 15 46 5 1 5 5 15 8 24 33
65
Table 3. 2. Means ± one standard error of habitat structure variables used for the logistic regression model. Data describing habitat structure of open forests were collected from each fire treatment site. Occupied trees were known to contain frillneck lizards, and unoccupied, randomly selected trees were assumed not to contain frillneck lizards.
Variable Unburnt Early frre Late fire
occupied unoccupied occupied unoccupied occupied unoccupied
Tree height (m) 12.2 ± 0.6 1 1 .5 ± l .O 13.7 ± 1 .0 10.9 ± 1 .2 15 .8 ± l .O 16.0 ± 1 .3
Trunk diameter 17.3 ± 1.2 17.1 ± 1 .8 16.9 ± 1 .3 18 . 1 ± 2.6 23.0 ± 2.4 22.3 ± 2.0
(em)
Liner cover 8.5 ± 0.3 8.0 ± 0.3 7 . 1 ± 0.4 6.5 ± 0.4 5 .5 ± 0.2 5.0 ± 0.3
Bare ground (%) 1 . 8 ± 0.5 0.8 ± 0.4 8.8 ± 1 . 6 10 . 1 ± 2.7 17.6 ± 1 . 4 1 9 . 5 ± 2.6
Tree canopy 2.7 ± 0.2 2 .8 ± 0.2 3.3 ± 0.1 2.3 ± 0.4 3.2 ± 0. 1 2 .4 ± 0.2
Ground 26.5 ± 2 . 1 31.3 ± 3.4 2 1 . 4 ± 1.3 32.2 ± 2.3 25.7 ± 1 . 6 44.2 ± 3.6
vegetation density
(25 em)
Ground 9.3 ± 0.9 10.2 ± 1 . 5 9 . 5 ± 0.9 17.6 ± 1 . 3 10.6 ± 1 . 2 20.3 ± 2 . 1
vegetation density
(50 em)
Ground 1 . 7 ± 0.3 1.5 ± 0.4 1.6 ± 0.4 3.2 ± 0.5 1.7 ± 0.4 2.9 ± 0.5
vegetation density
(100 em)
Ground 0.4 ± 0. 1 0.5 ± 0.2 0.2 ± 0.01 0.9 ± 0.3 0.4 ± 0. 1 0.3 ± 0 . 1
vegetation density
(150 em)
No. trees (n) 78 39 38 30 61 35
66
Table 3 . 3 . Logistic regression model for occupancy of trees by telemetered frillneck lizards during the dry sea_son. x2 values refer to difference in scaled deviance from total deviance of the null modeL The % total deviance is the proportion of scaled deviance from the total deviance of the null modeL Treatment (site) factors are represented in the model by: (1) early dry season site; (2) late dry season site; and (3) unburnt site.
Term Coefficient SE x2 DF p % total deviance
n = 282
Constant (1) -2.352 1.017
Tree canopy 3.437 0.835
+ (Tree canopy)2 -0.513 0.137 32.26 2 <0.001 8.66
Vegetation density (25cm) -0. 106 0.028 23.6 <0.001 6.34
Trunk diameter -0. 1 83 0.064
+ (diameter)2 0.003 0.001 6.36 2 <0.05 1 .71
Tree height 0.313 0 . 1 14
+ (Tree height)2 -0.007 0.003 6.21 2 <0.05 1.66
Tree canopy x Treatment 12.58 2 <0.01 3.38
(2) 0.011 0.304 n.s.
(3) -0.737 0.251 <0.01
Vegetation density (25 7.83 2 < 0.05 2 . 1 1
em) X Treatment
(2) 0.025 0.312 n.s.
(3) 0.094 0.029 <0.01
67
overall model. Figure 3.6 illustrates the relationship between the probability of occupancy
and the fined values of these four variables.
The probability of occupancy of a tree by C. kingii was highest in trees with a canopy
cover of 25-50% in the unburnt site. The probability of occupancy of trees by C. kingii in
both the early and late fire sites was highest in trees with 50-75% canopy cover.
Importantly, trees with a very light canopy in the unbumt site had a high probability (P =
0.5) of occupancy by lizards, whereas trees with a light canopy from both the burnt sites
showed a low (P = 0.1) probability of occupancy by lizards (Figure 3.6). The similarity of
the relationship between both burnt sites should be noted considering the large differences
in the intensity of the early and late dry season fires.
The probability of occupancy of trees increased with decreasing density of ground
vegetation (Figure 3.6) at all sites. However, this relationship was stronger in both burnt
sites, in which the probability of occupancy is small (P < 0.5) for trees with a medium
density (> 75 stems per m2) layer of grass at 25 em above the ground. The probability of
occupancy by lizards is high (P > 0.5) for trees in the unburnt site that have a moderately
dense grass layer (> 165 stems per m2).
The relationship between the probability of occupancy of trees and the variables tree height
and trunk diameter were similar for all three sites. A complex relationship appears to exist
between these two variables. Inspection of probability curves for these variables (Figure
3.6) shows no clear pattern, except that the probability of occupancy is relatively high (P
> 0.5) for all fitted values from either variable.
68
.9 (Q) 1.0 � (\v) > • > (.) .8 (.) c . . . . . • • c · ... \. co ro .8 0. .7 0. :J ::l (.) (.) (.) .6 (.) 0 0 .6
0 .5 -·. 0 ..... \ > .2;- .4 � .4
..0 ..c ·� co .3 ro . .. \... ..0 ..c .2 e .2 0
·' � a.. a..
.1 • . · . • 0.0 •• .......... ...... � 0.0 . . . . . . ·
0 1 2 3 4 5 0 1 5 30 45 60 75 90 1 OS 120
Canopy cover Vegetation density (stems per m2 ) 1.0 �) 1.0 Cd) � >.
c (.) ro .8 c 0. ro .8 ::l 0. (.) ::::s (.) (.) 0 .6 (.)
0 .6 -0 • - • 0 Z' .4 .?:- .4
..0 ..c co ro ..0 2 ..c .2 0 I- 0 a.. �
a.. 0.0 0.0
I 0 10 20 30 40 so 60 70 80 0 5 10 1 5 20 25 30 35
Tree d iameter (em) Tree height (m)
Figure 3.6. The effect of significant variables in a logistic regression model on the occupancy
of trees by frillneck lizard during the dry season. The graphs show changes in
estimated probability of occurrence of frillneck lizards with changes in (a) tree
canopy; (b) the ground vegetation density at 25 em; (c) trunk diameter; and (d) tree
height. Eor each relationship the values of other variables in model are fixed at the
mean value. For graphs (a) and (b), solid lines represent the unburnt site, dashed lines
are the early dry season fire site and dotted lines are the late dry season fire site.
69
There were no significant differences among the fire treatment sites with respect to the
selectivity indices of tree species during either the wet or dry seasons (Kruskal-Wallis: dry
season, z = 0.42, P = 0.809; wet season, z = 0.55, P = 0.774). The selection of Eucalyptus
tetrodonta was consistently high in all three sites (wet and dry season), except in the
unburnt site during the wet season (Table 3.4). Selectivity of E. tetrodonta in the unburnt
site was reduced in the wet season, and this was offset by an increase in selection of the
sand palm, Livistona humilis.
A total of 226 stomach samples were collected from all three sites during dry and wet
seasons, including 78 stomach samples used in the analysis of the short-term effects of fire.
The total volume and the number of items in the dry season stomach samples were not
significantly different among the three treatments (ANOVA: total volume, F2.143 = 0.37, P
= 0.699; number of items, F2.J.H = 1 .58, P = 0.226). The distribution of the number of
invertebrate orders and the number of prey size classes in dry season stomach samples
were also not significantly different among the three fire treatment sites (Kruskal-Wallis:
number of orders, z = 4. 1 8, P = 0. 12; number of size classes, z = 3.35, P = 0.12) (Figure
3.7 and Figure 3.8).
Wet season stomach samples also showed a high degree of similarity among the three
treatments. The total volume and number of items in the stomach contents were not
significantly different among the sites (ANOVA: total volume, F2•81 = 0.71, P = 0.499;
number of items, F2.81 = 0.47, P = 0.630). The distribution of the number of prey size
classes in wet season stomach samples (Figure 3.8) did not differ significantly among the
three treatments (z = 5.23, P = 0. 1 5 1 ). There was, however, a significant difference in
70
Table 3.4. Selectivity indices for tree species used by frillneck lizards within each site during the wet and dry seasons.
Unburnt Early fire Late fire Tree species Dry Wet Dry Wet Dry Wet
Eucalyptus tetrodorua 0.22 0.08 0.25 0.29 0.44 0. 17
E. porrecta -0.01 -0.05 0.04 -0.04 -0.07 0.03
E. miniara -0.04 -0.06 -0.12 -0.16 -0.16 -0. 14
Erythrophleum chlorostachys -0.02 -0.01 -0.06 -0.03 -0.01 0.01
Terminalia ferdirumdiana -0.02 -0.02 -0.02 -0.04 -0.01 0.02
Livistona humilis 0.07 0.25 0.03 -0.01 -0.02 -0.02
Dead" 0.03 0.02 -0.07 -0.07 -0.16 -0.07
Other' 0.01 -0.09 -0.09 -0.02 -0.05 -0.05
a. all dead trees m sample regardless of species b . species with low relative abundance ( < 0.05) were combined into this group
7 1
...- 50
� 0 -
en Q) 40
c.
E ro en
� (.) ro E 0
+J (/)
...- 50
� 0 -
en 40 Q)
c.
� 30 en
� � 20
E 0 U5 1 0
Dry season
0 1 2 3 4 5
Nu mber of prey size classes
Dry season
0 1 2 3 4 5 6 7 8
Number of invertebrate orders
Figure 3.7. Relative abundance of the number of prey size classes and invertebrate orders
present in the stomach contents of frillneck lizards for each fire regime in the dry
season. Open bars represent unbumt treatment, hatched bars rising right are early fire
treatment and hatched bars rising left are the late fue treatment.
72
- 50
� 0 -
Cl) <1) a. E ro Cl)
£. (.) ro E 0
� CJ)
-
� 0 -
Cl) <1) a. E ro Cl)
£. (.) ro E 0
� CJ)
40
50
40
30
20
1 0
0
Wet season
0 1 2 3 4 5
N umber of prey size classes
Wet season
1 2 3 4 5 6 7 8
Number of invertebrate orders
Figure 3. 8. Relative abundance of the number of prey size classes and invertebrate orders in
the stomach contents of frillneck lizards for each fire regime in the wet season. Open
bars represent unburnt, hatched bars rising right are early fire treatment and hatched
bars rising left are the late fire treatment.
73
the number of invertebrate orders (Figure 3.7) present in stomach samples among the sites
(z = 9.57, P = 0.022). Inspection of Figure 3. 7 indicates that the stomach samples from the
early fire site have a greater proportion of six or more invertebrates orders present.
The taxonomic composition was broadly similar among the three fire treatments during the
dry season (Table 3.5). Isoptera (termites), hymenoptera (ants) and chilopoda (centipedes)
were the most common prey taxa at all sites. Stomach samples collected in the unburnt site
recorded a higher occurrence of termites than the early and late fire stomach samples. The
relative volume of termites was also high in stomach samples from the unburnt site,
compared to the samples from the early and late dry season fire sites. Ants formed a large
proportion of late fire site stomach samples in terms of relative abundance, compared to
the other two sites. Orthoptera (grasshoppers) were frequently present in late fire site
stomach samples, and constituted most of the relative volume from this site.
Wet season taxonomic composition of stomach samples showed some variation among the
three fire treatments (Table 3.6). Termites, caterpillars and ants were the most commonally
taken prey items at all sites. Termites frequently occurred in stomach samples at all sites,
and the relative volume of termites was again much higher in the unbumt site. Termites
were regularly present in stomach samples from both late and early fire sites, but the
relative volumes were lower than the unburnt site. The relative volume of lepidopteran
larvae (caterpillars) is partly responsible for this difference with both fire sites (early and
late dry season) recording a high relative volume of caterpillars, whereas the unburnt site
recorded a substantially lower relative volume of caterpillars (Table 3.6).
74
Table 3.5. Dry season stomach contents of frillneck lizards from the three fire treatment sites.
Prey taxon Unburot Early fire Late fire Occurrence Abundance Volume Occurrence Abundance Volume Occurrence Abundance Volume
(%) (%) (%) (%) (%) (%) (%) ( % ) ( % )
lsoptera 70.3 85.25 63.7 33.2 84.07 42.0 27.1 48.3 16.3
Orthopetra 4.0 0.03 0.2 14 0.61 12.13 37.0 1.54 23.28
Hemiptera 8.3 0.22 2.45 35.5 0.39 1.38 8.4 2.0 4.6
Coleoptera 16.6 0.19 2.96 26.0 0.98 4.94 13.5 0.56 2.12
Diptera -- -- -- 3.2 0.26 0.36 3 .4 0.56 0.7
Lepidoptera 17.0 0.15 3.39 4.0 0.53 1 1 .03 18.6 12.30 4.34
Hymenoptera 54.0 13.73 3.42 66.2 12.26 2.65 73.0 44.76 9. 1 1
Blattodea -- -- -- 1 .6 0.05 1.63 1 .7 0.21 0.35
Mantodea 4 . 1 0.03 2.83 -- -- -- 1 .7 0.03 1.05
Odonata 4 . 1 0.03 2.83 -- -- -- 5.0 0.14 2.8
Phasmotodea 4 . 1 0.03 1 .85 4.9 0.08 2.45 6.8 0.28 6.35
Aranea 8.3 0.06 0.7 13 . 1 0.24 2.05 5.0 0 . 1 1.54
Chilopoda 25.0 0.22 15.65 24.5 0.47 19.2 39.0 0.98 27.3
Gastropoda -- -- -- 1 . 6 0.02 0.4 5.0 0 . 1 1.05
other -- -- -- -- -- -- 3.0 0.08 0.7
totals n = 24 n = 2644 106 (ml) n = 61 n = 3774 244 (ml) n = 59 n = 2855 283 (ml)
particular prey taxon, expresseo as a percentage or tne numoer or stomach samples examined. Abundance is the percentage of the number of items in each particular prey taxon. Volume is the percentage of the total estimated volume of all items. -
denotes prey taxa not recorded in sample.
tn r-
Table 3 .6. Wet season stomach contents of frill neck lizards from the three fire treatment sites.
Prey taxon Unburnt Early fire Occurrence Abundance Volume Occurrence Abundance Volume
(%) (%) (%) (%) (%) (%) Isoptera 65 89.04 37.30 5 1 .6 64.28 12.96
Orthopetra 30 0.32 6.80 5 1 .6 1 .30 9.77
Hemiptera 20 0.96 2.85 12.4 1 .08 2.53
Coleoptera 65 1.87 7.09 58.1 2.27 4.63
Diptera 5 0.04 0.03 4.6 0.21 0. 18
Lepidoptera 55 3.33 28.65 60 1 1 .33 36.91
Hymenoptera 70 3.88 0.83 80.6 16.15 4.13
Blattodea -- -- -- 3.2 0.32 0.71
Mantodea -- -- -- 3.2 0.05 0.31
Odonata -- -- -- 9.7 0 . 16 3 .21
Phasmotodea -- -- -- 3.2 0.05 0.31
Aranea 10 0.09 0.01 12.9 l.O 0.85
Chilopoda 30 0.36 14.92 5 1 .6 1.62 23.06
Gastropoda 20 0.09 1.32 6.45 0.01 0. 1
other - - - - -- -- -- --
totals n = 20 n = 2191 150 (ml) n = 31 n = 1845 280 (ml)
Late fire Occurrence Abundance
(%) (%) 60 77.61
16.7 0.58
16.7 0.83
36.7 0.62
-- --
67.7 13.20
56.6 5.75
10 0.16
-- --
6.70 0. 12
3.30 0.08
16.70 0.37
26.7 0.50
6.70 0.08
3.3 0.04
n = 30 n = 2416
Volume
(%) 17.04
9.35
2.02
1.43
--
53.53
0.75
0.70
--
3.01
0.90
0.42
9.96
0.6
0.3
331 (ml)
\0 t-
A total of 4227 invertebrates were collected by sweep-netting from April 1992 to February
1994 from the three fire treatment sites (Table 3.7). The abundance of invertebrates was
greater for the wet season sample, comprising 71 .8% of total items. The invertebrate orders
and their proportion in the sample were broadly similar among the three fire treatment
sites. Importantly, two prey taxon (termites and centipedes) which represent over 80% of
the relative abundance and over 50% of the relative volume of stomach contents (Table 3.5
and 3.6), were not sampled using sweep-netting. Therefore, the prey availability data
presented in Table 3.7 represents only a portion of the food available to the frillneck
lizards. Hymenoptera was the most common invertebrate order at all three sites in the wet
and the dry seasons. The relative abundance of orthoptera increased during wet season
samples at both early and late fire sites, but remained constant between seasons in the
unburnt site. Conversely, the decrease in relative abundance of hymenoptera was small in
the unbumt site compared to the relatively larger decrease of hymenoptera in both fire
sites, in the wet season samples.
Body condition was analysed separately for males and females because males are
significantly heavier at a given body length than females (Chapter 2: Body condition).
Adult male body mass at a given length was significantly different among the three
populations, but only during the wet season (dry season, F�,82 = 2.65, P = 0.075; wet
season, F1•56 = 4. 1 5, P = 0.018) (Figure 3.9). Tukey's comparison of means test indicated
that males from the unburnt site had significantly lower body condition than either of the
burnt sites during the wet season. Adult female body mass at a given body length was
significantly different during the wet season, (F .. 65 = 4.33, P = 0.0 17) (Figure 3. 10).
Tukey's comparison of means test indicated that females from the unburnt site have
77
Table 3 .7 . Relative abundance of prey taxon obtained from sweep-netting in each of the three fire treatment sites, during the dry and wet seasons. Samples from both years are combined. Taxa denoted with (--) were not recorded from sweep-netting but were recorded in the stomach contents of frillneck lizards.
Prey taxon Unburnt
Dry Wet Dry
Early fire
Wet
Late fire
Dry Wet
Abundance Abundance Abundance Abundance Abundance Abundance (%) (%) (%) (%) (%) (%)
Isoptera -- -- -- -- -- ·-
Onhopetra 1 1 .2 12.9 6.5 33.7 7.8 23.2
Hemiptera 7.5 7.7 16.0 8.6 14.9 6.3
Coleoptera 9.4 22.3 16.2 18.0 14.0 24.0
Diptera 10.7 6.6 5.9 6 . 1 10.6 7.3
Lepidoptera 2.3 3.2 1 .4 5.5 0.7 9.3
Hymenoptera 41 .4 27.7 39.7 12.1 36.8 10.8
Blanodea 0 1 . 3 0 1 .0 0.2 1 .7
M.antodea 0.5 0.1 0 0 0 0.2
Odon.a.ta 2 . 1 3 . 0 0.5 1 .0 1.4 0.9
Pb.asmotodea 0.8 1 .0 1 .4 4.6 0 6.4
Aranea 14.1 14.1 12.4 9.2 15.8 9.7
Chilopoda -- -- -- -- -- --
Gastropoda -- -- -- -- -- --
other -- -- -- -- -- --
total no. items 384 834 370 1043 435 1 161
78
. 1 0 D ry season
39 .05 30 ! en f -
ro ::l 0.00 14 "0 en Q)
-.05 0::: -. 10
-. 1 5
Unburnt Early fire Late fire
. 1 0 Wet season
.05
en - 56 ro 32 ::l 0.00
"0 en Q) -.05 0::: 1 3
I -. 1 0
-. 1 5
Unburnt Early fire Late fire
.Fire regimes
Figure 3 . 9. Mean residuals of linear regression of log-body mass with log-SVL for adult male
frillneck lizards in each of the fire treatments, during the dry and wet seasons.
Numbers are sample sizes and error bars are one standard error. Line through zero
represents the best least squares fit.
79
en -
ro =:J
"'C en Q) 0:::
en -
ro =:J
"'C en Q) 0:::
. 1 0 ,... Dry season
.OS 1 8
1 7
0.00 t----------+------t--
-.OS 3
f -. 1 0 f-
-.1 s 1------,-----,.-----r---Unburnt Early fire Late fire
. 1 0 Wet season
32 .OS f
0.00 25
-.OS
I -. 1 0
-. 1 S
Unburnt Early fire Late fire
Fire regimes
Figure 3 . 10. Mean residuals of linear regression of log-body mass with log-SVL for adult
female frillneck lizards in each of the fire treatments, during the dry and wet seasons.
Numbers are sample sizes and error bars are one standard error. Line through zero
represents the best least squares fit.
80
significantly lower mean residuals than the late fire site, but not the early fire. Low
samples sizes from the dry season population precluded statistical analysis of these data.
DISCUSSION
The results presented here show that dry season fires have a substantial influence on the
ecology of frillneck lizards, and this effect was different between the two types of fires.
The short-term effects of fire on frillneck lizards were considerably greater than the longer
term effects.
Short-term effects of fire
The mortality of frillneck lizards during early dry season fires was low compared to the
late dry season fires, in which a substantial proportion of marked lizards died. Remaining
perched in the tree canopy offers sufficient shelter for lizards during early dry season fires.
Late dry season fires force lizards to take a more evasive response, with most lizards
leaving their pre-fire location and either sheltering in larger trees or in hollow termite
mounds on the ground. The use of termite mounds offers sufficient protection from fue,
as all frillneck lizards that used them survived the high intensity fires. Many other
vertebrates and invertebrates shelter in termite mounds during fires (Braithwaite 1990, pers.
obs.). They are an important refuge during fires for Ch/amydosaurus, because there are no
other refuges in this habitat which are large enough for adult lizards. Frillneck lizards are
exposed to a greater risk of mortality by remaining in the tree canopy during late dry
season fires because these fires regularly scorch the canopy.
8 1
Direct mortality of lizards during fire has generally been assumed to be low (Erwin and
Stasiak 1979, Means and Campbell 1981 , Bamford 1986). This is based on the assumption
that the lizard fauna can escape fire by sheltering in burrows, crevices, or other available
shelter. These conclusions are based on changes in abundance of lizard species after single
prescribed or wild fires, and may be influenced by other factors such as predation and
migration. The results from this study clearly show that mortality during fire can be either
high or low within a single species of lizard depending on the intensity of fire. This study
also documents that a range of behaviours are used by a single species of lizard when
sheltering from fire, and the behavioural response is affected by fire intensity.
Frillneck lizards move into or remain in open areas produced by fire. Population density
over the two year period was higher in both burnt sites than the unburnt site (Chapter 4:
Population size and density). This suggests that frillneck lizards remain in the burnt habitat.
The selection of open habitat after fires has been documented for other species of agamid
lizards in a variety of environments within Australia. The small agamid Diporiphora
bilineata, which occurs in sympatry with Chlamydosaurus kingii in Kakadu National Park,
increased in abundance after early dry season fires (Braithwaite 1987, Trainor and
Woinarski 1994). Ctenophorus ine1mis, which inhabits hummock grasslands of arid regions
exhibited a dramatic increase in abundance following fire (Pearson unpublished data, Dell
and How unpublished data). However, other agamid species present in hummock grassland
showed a decrease in abundance following fire (e.g. C. isolepis; Pearson unpublished data).
In recently burnt mallee, Amphibo/urus pictus is a common species (Caughley 1985 ) .
Another study in mallee habitat found twice as many Amphibolurus fordi on burned sites
as unburned sites (Cogger 1 984).
82
The family lguanidae is analogous to the Australian agamids in many respects (Stamps
1983, Pianka 1986 ). Some species of iguanids also select open habitat resulting from f1res.
Sce/oporus occidentalis shows a preference for perching on burned shrubs, whereas they
are usually found on the ground in unburnt habitat (Lilywhite and North 1974). A separate
investigation of this species concluded that burnt habitat was preferred (Kahn 1960)
although only a small sample was studied.
The selection of open areas resulting from fires is not restricted to these two reptile
families. Lizard species from other families also show a preference for recently burnt areas
(Fyfe 1 980, Caughley 1985, Mushinsky 1985). Numerous bird species in northern Australia
colonise recently burnt areas because of increased access to food resources (Braithwaite
and Estbergs 1987, Woinarski 1990).
The volume of stomach contents in frillneck lizards increased in the week after early and
late dry season fires, although this was only significant after the late dry season fires.
However, there was only a small change in number of items in the stomach contents after
both fire treatments. The number of prey size classes in the stomach contents increased one
week after both fire treatments, but again only the late dry season fire was significant.
Thus, even though lizards captured an equal number of prey items before and after fire,
they are able to capture a greater range of prey sizes, which increases the volume of their
stomach contents.
The abundance and diversity of invertebrate prey taxa were not sampled directly after frre
in this study. However, research from a tropical savanna in Africa revealed an overall
83
decrease in abundance and a minor decrease in diversity of invertebrates immediately after
ftre (Gillon 1983 ). The high intensity of late dry season fires would possibly have a similar
effect on the overall abundance of invertebrates. Frillneck lizards increase the volume of
food taken after ftres, whether or not there is a change in invertebrate abundance related
to fire. The fact that this increase in volume is greater after the late dry season ftres,
suggests that removal of ground vegetation after these fires increases the accessibility to
food resources.
An understanding of the foraging behaviour of this species supports this argument. They
are "sit-and-wait" predators that perch on vertical tree trunks (Shine and Lambeck 1989,
Chapter 2: Diet, Habitat use). From this position they visually locate invertebrate prey,
descend to the ground to capture the prey, and then return to their vertical position on the
tree trunk. A decrease in the density of ground vegetation would assist them in visually
locating prey and increase the mobility of lizards while feeding on the ground.
The change in relative abundance of invertebrate orders present in stomach contents was
small after early dry season fire, but late dry season ftres resulted in a greater increase. The
relative abundance of termites decreased by over 40% after late dry season frres and this
was offset by a large increase in ants. The foraging activity of termites is decreased by the
removal of grass which is their main food resource. Ants are prevalent in recently burnt
areas within this habitat (Andersen 1991). This is possibly reflected in the diet of
Chlamydosaurus. It should be noted that ants actually decreased in relative abundance in
the early fire treatment stomach samples, and only increased after the late dry season ftres.
This suggests that ants may be more active or abundant after the late dry season fires
84
because of the more open habitat, which is favoured by some species, i .e., Iridomyrmex.
Longer-term effects of fire
The effect of fire on the vegetation structure of open Eucalypt forests in northern Australia
is complex, and remains unclear and contentious among researchers. Previous authors
suggest that because of the many complex relationships between the vegetation and edaphic
factors, the effect of fire on vegetation is difficult to determine (Stocker and Mott 1 9 8 1 ,
Bowman et a/. 1988. Lonsdale and Braithwaite 1991 ). Exclusion of fire does not result in
closed forest community in the open Eucalyptus forests of northern Australia (Bowman et
a/. 1988). Preliminary data obtained from the Kapalga fire experiment suggest unburnt
forests maintain a homogenous canopy cover, whereas annually burnt forest have a
heterogenous canopy cover (R.J. Williams pers. comm.). Fire generally creates a
heterogenous habitat, which may create a wider choice of habitats for frillneck lizards to
use.
The probability of occupancy of trees by frillneck lizards increased with a thicker canopy
and less ground vegetation. The amount of canopy cover of trees selected by frillneck
lizards may influence their thermal relationships. Frillneck lizards thennoregulate carefully
in their environment, reducing their midday body temperature by 4oC during the dry season
(Christian and Bedford 1995). Assuming a heterogenous canopy cover in annually burnt
areas, the selection of trees with thicker canopies suggests that these trees are possibly
preferred by frillneck lizards. Lizards in habitat unburnt for several years select trees with
a more open canopy, which may be associated with more open habitat The suitability of
these trees for thermoregulation is unclear and would warrant further investigation.
85
The preference for trees surrounded by a low density of ground vegetation possibly relates
to the foraging strategy of frillneck lizards. As suggested in the analysis of short-term
effects of fire, a decrease in ground vegetation may enable lizards to access a greater
variety of different sized prey. Even before fires, the lizards prefer areas with less grass
in all three fire regimes (Figure 3.6). The avoidance of densely vegetated areas around
creeks and rivers by frillneck lizards (Shine and Lambeck 1989) supports this conclusion.
The variation in overall stomach contents (i.e. total volume, number of items, number of
orders and prey size classes) among the three fire treatments during both wet and dry
season was small. However, there were some important differences in the type of prey taxa
eaten by frillneck lizards. Termites remain a primary food source for frillneck lizards in
the unburnt site in both the wet and dry seasons. The proportion of termites in the stomach
contents was lower in the early and late dry season fire sites. Harvester termite
(Trinervitemzes and Cubitermes) abundance in a tropical African savanna habitat decreased
following fire due to the decrease in food availability for termites (grass and leaf litter)
(Benzie 1986). A similar relationship in this savanna habitat is possible. The removal of
dry grass by dry season fires may reduce the abundance of harvester termites, and therefore
reduces their availability to frillneck lizards over the dry season and the following wet
season.
The predominance of lepidopteran larvae (caterpillars) in the wet season stomach contents
exhibited substantial difference among the fire treatments. The stomach contents from the
late fire site in the wet season were dominated by caterpillars. Caterpillars were less
important in early fire samples, and caterpillar abundance was lowest in the stomach
86
samples from the unburnt site. Sweep-netting for invertebrates during the wet season
months failed to reveaJ any major differences among sites with respect to the abundance
of caterpillars. Therefore, the reason for the difference in abundance of caterpillars among
the fire treatments remains unclear.
Given the similarity in total volume of stomach contents among the populations in the three
fire regimes, it is surprising to find a significant difference in the body condition for both
maJes and females among the three sites during the wet season. The wet season is a period
of increased activity and high field metabolic rates, as well as being the reproductive
season. Possible differences in the types of invertebrate orders eaten in the wet season may
account for differences in body condition. The time spent foraging was not investigated in
this study, but may be an important factor in influencing body condition. Generally, lizards
use areas that have a lower density of grass. Fires create more of these areas and the open
areas may increase the ease of capture of prey. There was no difference in body condition
during the dry season. Access to larger prey may only last a short time after the dry season
fires, therefore dry season body condition may not be affected.
Fire is important in maintaining the relatively open habitat that is preferred by
Chlamydosaurus kingii. The exclusion of fire has been implicated as a possible reason for
reduced size and growth rate in a peripheral population of a North American lizard,
Crotaphytus collaris (Sexton er a/. 1992). Complete fire exclusion is unrealistic in northern
Australia, where fire is extremely common. Early dry season fires are possibly the most
beneficial to Chlamydosaurus as mortality is low and a more heterogenous habitat
(containing preferred open areas) is created. The long-term viability of populations in areas
87
that are repeatedly burnt during the late dry season is unclear, although the 30% direct
mortality suggests that a population will decrease if these fires are repeatedly applied over
an extended period (greater than 5 years). The relatively high densities of frillneck lizards
within the late fire sites (Chapter 4: Population dynamics) and numerous adult females
suggests that these populations are viable at the present time. Migration is a crucial factor
in assessing the viability of populations, and it has not been discussed in this paper. The
distances moved by these lizards can be substantial during the wet season (Shine and
Lambeck 1989, pers. obs.). However, the greater the area burnt during a late dry season
fire, the less migration will occur into the centre of the area. Therefore, restricting the area
burnt during late dry season fires will ensure migration is relatively easy for this species.
Summary
In summary, fire has a clear effect over a short period of time, and a less obvious effect
on the ecology of Chlamydosaurus over a number of years. The intensity of fires influences
the level of the behaviour, mortality and diet. The general diet shows no clear differences
among different fire regimes. Overall, frillneck lizards occupy trees with relatively thick
canopy cover surrounded by a low density of grass and shrubs. Lizards inhabiting fire
excluded habitat show differences in the occupancy of trees, which is related to fire
induced changes to the vegetation structure. Differences in condition among the three fue
regimes may be related to differences in prey taxa taken, or potential differences in energy
budgets related to foraging or reproduction.
88
Chapter 4 The demography, population dynamics and dry season home range of
frillneck lizards, with reference to the effects of three different fire regimes.
INTRODUCTION
The study of species population dynamics is essential to understanding life-history
strategies. The primary cause of similarities in general life-history strategies among species
are their phylogenetic relationships, particularly at the family level (Stearns 1984, Dunham
and Miles 1985). Variation of life history within families is largely based on phenotypic
responses to environmental conditions (Ballinger 1983 ).
The subject of this study, Ch/anzydosaurus kingii, belongs to the family Agamidae. A total
of 64 species of agamids inhabit Australia. Nine species, including Chlamydosaurus, have
large body sizes (snout-vent length > 150 mm) and represent some of the most spectacular
members of this continent's diverse reptile fauna. The taxonomic relationships among the
large agamids suggest differences in their biogeographic origins. Hypsilurus and
Physignathus are restricted to moist habitats along the east coast of Australia (Cogger
1992). The existence of other species in the same genus (with a similar karyotype)
throughout southern Asia, indicates that they originated from Asia (Witten 1982, 1983).
Pogona and Chlanzydosaurus represent the large Australian agamids which have an
extensive distribution throughout Australia, but predominate in the arid and tropical
climatic regions (Cogger 1992). They share many morphological and genetic characteristics
with the other smaller Australian agamids, and it is most probable that their evolution has
taken place entirely within Australia (Witten 1983, Greer 1989).
89
The population dynamics of large agamid lizards in Australia is poorly understood. A
recent demographic study on the eastern water dragon, Physignarhus lesueurii represents
the first published data on the population ecology and demography of the Asian lineage of
Australian agamids (Thompson 1993 ) . The only published information on the population
dynamics of the lineage of large agamids that evolved in Australia is for C. kingii. The
population dynamics of the genus Pogona is even more poorly understood. This lack of
demographic information for large agarnids in Australia makes analyses of familial trends
in life history strategies difficult.
Shine and Lambeck's ( 1 989) study of the ecology of C. kingii established some basic
demographic information for this species. The reproductive cycle of males and females, and
body size at sexual maturity were determined using museum specimens. Additional
reproductive data is available on the incubation periods, hatchling size, clutch size and
clutch frequency (Bedford et a/. 1993).
This study has two principal aims: ( 1 ) to further document the demography and population
dynamics for this species; and (2) to examine some possible effects of fue on aspects of
the population dynamics. This information will facilitate future research concerning the
evolution of life history strategies of large agamids in Australia. Specifically, data on the
general reproductive cycle, growth, age, population structure, density, home ranges and
intraspecific interaction will be examined for Chlamydosaurus kingii. Where sample sizes
permit, analyses on the possible effects of fue have been included.
90
METHODS
Sampling
For a full description of the site and climate see Chapter 2 (Methods). Frillneck lizards
were monitored using both telemetry and mark-recapture, and both methods are described
in Chapter 2 (Methods).
Reproductive biology
The presence of oviductal eggs in females was determined by palping the abdomen. This
method is sufficiently accurate for determining whether the lizards were gravid or not.
Data over the two reproductive seasons sampled were combined to establish an annual
reproductive cycle. The small sample size prevented comparison of variability in the
reproductive cycle on a site and yearly basis. The age and size at sexual maturity were
determined from the recapture of permanently marked hatchlings. Minimum longevity of
C. kingii in the field was determined from the recapture of permanently marked and fully
grown adult lizards.
Growth and age
The growth rates of frillneck lizards were measured by the change in snout-vent length
(SVL) between the initial capture and the last recapture of an individual. Growth rates are
expressed in mm day"1 • The mid-point of the SVL between the initial and last recapture
was also calculated for further analyses between sexes and sites. The age of lizards within
a certain SVL size class were estimated using growth rates and the SVL at hatching.
9 1
Population dynamics
The SVL at initial capture of all individual lizards were used to determine the population
structure of C. kingii at each fire treatment site. Lizards were grouped into one of ten size
classes using 25 mm SVL intervals. Sex ratio (number of males/number of females) was
calculated using these data.
Population estimates of C. kingii were calculated using recapture data for the three sites.
Lizards monitored using telemetry were omitted from these analyses because their
recaptures were non-random. An underlying assumption of most population estimate
models is the equal catchability of individuals within the population (Caughley 1977, Krebs
1989). Behavioural differences in C. kingii between the wet and dry seasons make this
assumption difficult to meet (Chapter 2: Results). A variety of population estimate models
were applied to the mark-recapture data because of this seasonal variability. Three
frequency of capture distribution models were used: poisson; negative binomial; and
geometric distribution (Caughley 1977). An additional jackknife estimate was also used due
to the unequal distribution of some of the recaprure data (Chao 1988). The following
assumptions were made for each of the three populations: the populations were open (birth,
deaths and migration occurring throughout time); that marked and unmarked lizards were
equally catchable; and sexes were equally catchable. To determine the 'most' accurate
population estimate, a 'goodness of fit' test was applied between the observed recapture
data and the expected values calculated by each of the three frequency distribution models
(not applied to the jackknife estimate). A model that is significantly different to the
observed data will produce a poor estimate of population size (Caughley 1 977).
92
Densities of C. kingii were calculated by dividing the population size estimate (N) of each
fire treatment site by the area (ha) of each site. James ( 1 99 1 a) describes this as a "naive
density", as it is not strictly an absolute density. Sites were based on a network of roads
and were irregular in shape. The area of each site was estimated by multiplying the total
length of the roads by the width of the area surveyed. The length of each road was
measured using a vehicle's tachometer. The width of the area was measured as the
distance between the centre of the road and the furthermost point from the road at which
a lizard was captured, and this distance was multiplied by two for total width.
Home ranges
Adult l izard home ranges were determined from locations of telemetered individuals during
a single dry season period (May to September). Home range analysis was restricted to the
dry season because the primary purpose of this exercise was to study the effect of
prescribed fires on home range size. Wet season home ranges have been reported
previously (Shine and Lambeck 1989). Lizards were located between two week and
monthly intervals, except during periods prior to and after prescribed fires when several
locations were recorded. The minimum number of locations needed to confidently predict
an animal's home range was determined by plotting the percentage of home range area
against the cumulative number of locations (Rose 1982). An asymptote is reached at 8
locations, which accounts for approximately 80% of an adult frillneck lizard's home range
in the dry season (Figure 4. 1 ) . Therefore, lizards with less than a total of eight locations
in the dry season were omitted from this analysis. Home ranges were calculated by the
minimum convex polygon method, using the computer program Wildtrak (Todd 1993).
Home ranges were not corrected for unequal number of locations.
93
1 00 • • • - I I -• :
I I • • I
80 I -.. • ! � I I i 0 ._... l Q.) • 0') 60 • I c I l I rn I....
Q.) • E 40 I I 0 I l
I • 20 I I I •
I I -
0 2 A. 6 8 1 0 . 1 2 . A. 1 6 I .
Number of locations
Figure 4. 1 . The percentage of home range estimated from the cumulative number of locations
collected in the dry season. Approximately eight locations are needed to describe 80%
of a frillneck lizards' dry season home range.
94
An index of movement within a home range was calculated by taking the mean distance
(m) of all relocation sites from the geometric centre of each individual's home range. This
produces a weighted measure of movement for each individual within their home range,
and reduces the effect of uneven intervals between relocation of transmittered lizards.
Analysis
Differences in growth rates between sexes and fire treatments were analysed by AN COY A
with mid-point SVL as a covariate. Contingency table analysis was used to test for
differences in the population structure of adult frillneck lizards among the three fire
treatments. Differences in home ranges between sexes were analysed using unpaired t-tests,
and one-way ANOV A was used to test for differences among fire treatments. All means
are presented with one standard error unless otherwise stated.
RESULTS
Reproduction biology
The mean SYL of gravid females was 202 mm ± 2.45 (n = 24). Gravid females represented
39% of all sexually mature females caught during both reproductive seasons sampled (n
= 60). There was no difference between the proportion of gravid females in each of the two
years sampled, with 42% (n = 25) gravid in the 1992-93 season and 37% (n = 35) gravid
in 1 993-94 season. Gravid females were flrst captured during early November in both
years, and this was also the month when the largest number of gravid females were caught
(Figure 4.2). Capture effort did vary among months and was highest
95
en (1) cu E � ......... ;:j
""0 cu
� 0 � (1)
..0 E ;:j
z
20
1 5
1 0
5
- Gravid I l Non-gravid
n Oct Nov Dec Jan F b M e ar Apr
Months
Figure 4.2. The number of gravid and non-gravid female frillneck lizards captured each month
during the wet season. Both reproductive seasons are combined.
96
during November. When capture effort (number of kilometres censussed per month) i s used
to weight monthly samples, December recorded the highest number of gravid females.
Gravid females continued to be captured until March, where a slight increase in the
proportion of gravid females occurred. Eight adult females were caught in both
reproductive seasons. From this sample, three were gravid in both seasons, three were
gravid for only one of two seasons, and two adult females were not gravid in either season.
Bedford et a/. ( 1993) recorded a minimum incubation period in the laboratory of 54 days
at 33·c and 73-80 days at 30"C. If an average of 60 days incubation period is used, the
earliest date of hatching is approximately the 1st of January each year, given the 1st of
November as the earliest date of oviposition. The latest possible date of hatching would
be approximately the 1st of June, given the 1st of April is the latest recorded date of a
gravid female in this population. Therefore, a considerable amount of variation in the age
of hatchlings (up to 6 months) is possible in any one year.
The earliest record of a hatchling C. kingii from Kapalga was April 1992, with a SVL of
55 nun. Bedford et a/. ( 1993) recorded a mean SVL of 48 mm (range: 42-51 mm) of
hatchlings hatched in the laboratory. Therefore, i� would be reasonable to assume that a
hatchling with an SVL of 55 mm would have emerged the previous month (March).
Hatchlings have a distinctly different color pattern compared to juveniles and adults. They
are grey with distinct uneven dark bands across their body. The ventral surface is white and
the frill is short In contrast, juveniles and adults develop a dark ventral surface, have a
predominant brown or reddish color and a relatively long frill. Only a small number of
hatchlings were captured throughout this study, possibly due to their small size, cryptic
97
behaviour and excellent camouflage.
A female hatchling was marked in August 1992, with a SVL of 94 mm. It was re-captured
in November 1993 with a SVL of 1 80 mm, and it was gravid. This recapture establishes
two important population parameters for C. kingii: ( 1 ) sexual maturity in females is
attained at an S VL of 180 mm; and {2) sexual maturity in females may occur during the
second year of a frillneck lizard's life. Shine and Lam beck (1 989) estimated size at sexual
maturity of females to be approximately 175 mm SVL.
Growth and age
Growth rates for male and female frillneck lizards are illustrated in Figure 4.3. The growth
rates were calculated over a mean of 174 ± 16.67 (n = 73) days. Juvenile frillneck lizards
(SVL <175 mm) grow significantly faster than larger adult lizards (juveniles, mean = 0.243
± 0.041 nun day·• , n = 6; adults, mean = 0.043 ± 0.007 mm day·• , n = 67; t = 6.94, DF =
7 1 , P < 0.000 1 ) (Figure 4.3). Males grow significantly faster than females (AN COY A:
slopes, Fu� = 0.5 1 3, P = 0.476; intercepts, F1.70 = 66.25, P < 0.000 1) . Female growth rate
decreases at a SVL of approximately 200 nun, after that growth is neglible. Males,
however, continue to grow until they reach a SVL of approximately 240 mm, after that
growth is neglible.
Analyses of growth rates of male lizards among the fire treatment sites showed no
significant difference (ANCOVA: slopes, F2.38 = 0.755, P = 0.477; intercepts, F2.40 = 0. 1 1 ,
P = 0.371 ). A comparison of female growth rates was not possible among the three
98
.4
....-.. 0 0 ..--I >-.
rn .3 "0 0 E E 0
..._... • 0 Q) .2 ...... 0 rn � - 0
..c • 0 ...... 0 3 • 0 0 0 . 1 0 0 �
CJ • • t • • • • • •
0.0 • • •
1 20 1 60 200 240 280
SVL (mm)
Figure 4.3. Growth rate of male and female frillneck lizards. The mid-point of SVL between
first and last recapture is used. Open circles represent males and closed circles
represent females.
99
fire treatments because of the low sample size in the unbumt site (n = 3). However, a
comparison of female growth rates between the early and late dry season frre sites showed
no significant differences in growth rates (ANCOVA: slopes, F1.'1A = 0. 1 29, P = 0.879;
intercepts, F us = 1 . 899, P = 0. 1 7 1 ).
By knowing the earliest date of emergence, the mean growth rate of lizards in each size
class and the date of capture, it is possible to estimate the age of an individual up to three
years. Individuals in the first year age cohort (hatchlings) range between a SVL of 50-140
mm. This estimate is based on a mean growth rate of sexually immature juveniles of 7.29
mm month·1 (n = 6). Therefore, hatchlings are able to grow approximately 90 mm in their
frrst 1 2 months. The SVL of individuals in their second year (juvenile) ranges between
1 40-200 mm, based on the same mean growth rate of the hatchling size class. Males grow
to a greater SVL than females in the second year because of their greater growth rate
(Figure 4.3). The differences in age classes becomes unclear at this point, but it is
reasonably safe to assume females with a SVL of 200 mm or greater, would be at least in
their third year of growth. Males do not reach an asymptote in SVL until 240 mm, which
would require a further year of growth. Therefore, males with SVL > 200 mm and < 240
mm are approximately three years of age, and males above 240 mm SVL would have a
minimum age of four years.
Minimum longevity of frillnecks in the field can be estimated from recapture data of
adults. An adult male with a SVL of 260 mm was marked in September 1991 and was
periodically recaptured until October 1993. Therefore, the approximate minimum age of
this individual is 6 years, given that it takes males four years to reach a SVL of 240 mm.
100
An adult female with a SVL of 205 mm was captured in December 1992 and recaptured
in March 1 994 with a SVL of 2 1 5 mm. The approximate minimum age of this female is
4.3 years, given it takes females two years to reach a SVL of 180 mm.
Population dynamics
The initial capture of all individual lizards was used to determine the population structure.
A total of 245 C. kingii were captured within the three fire treatment sites from April 1992
to April 1994 (Figure 4.4). A notable feature of all three sites is the general absence of
hatchling and juvenile lizards. This was due to their small body size and cryptic behaviour,
which increased the difficulty in sighting them. The relative number of adult lizards (SVL
> 175 nun) in each size class did not differ significantly among the three populations (X2
= 5.92, DF = 6, P = 0.435). Lizards in the 175-200 mm SVL size class were the most
numerous relative to the other size classes, in all three populations (Figure 4.4).
Only seven adult females were captured in the unbumt site compared to 34 and 39 in early
and late sites, respectively (Figure 4.4). Therefore, the potential reproductive output of the
population in the unburnt site is limited. The number of lizards with a SVL between 200-
225 nun in the late fire treatment site was low compared to the early fire treatment. This
may represent selective mortality of this size class during late fires.
The sex ratio of all captures from all sites was heavily biased towards males (m/f: 1.73 ).
This is possibly a result of greater visibility and mobility of large males as they defended
territories. The number of male and female frillneck lizards captured each month over two
101
40
35 Early fire 30
25
20
1 5
1 0
5
0
CJ) 75 125 175 225 275
"'0 45 ,_ ro 40
Late fire N 35 30
� 25 0 ,_ 20 Q) 1 5
.c 1 0
E 5 :::s 0
z 75 125 175 225 275
45 40 35
Unburnt 30 25 20
·,
1 5 1 0
5 0
75 125 175 225 275
SVL size classes (mm)
Figure 4.4. Number o f lizards in the di[f-.;rent size cohorts within each fire treatment site.
Open bars represent females, closed bars represent males and lined bars represent
juveniles and hatchlings.
102
years were tabulated to allow direct monthly comparisons of the sex ratio (Figure 4.5).
Considerable monthly variation is evident in the sex ratio which possibly reflects
differences in reproductive behaviour. The sex ratio of adult frillneck lizards among the
three fire treatments varied considerably. The unburnt site exhibited the largest male bias
(2.85), with early fire ( 1 .76) and late fire ( 1.85) treatment populations being slightly less
biased towards males.
Population estimates from each site were derived from four frequency of capture models
(Tables 4. 1 , 4.2 and 4.3 ). The geometric distribution model produced the best 'goodness
of fit' of the three frequency of capture models for each fire treatment site. The negative
binomial model was the least accurate showing highly significant differences with the
observed data. A 'goodness of fit' test was unable to be used for the unburnt site because
of insufficient recaptures. The jackknife estimate consistently produced estimates within
the range produced by Caughley's ( 1 977) "triple" frequency distribution of captures
method, and the jackknife estimate was selected for the calculation of frillneck lizard
density. The population estimate for the unburnt site is likely to be under-estimated due to
the large proportion of adult lizards (65%) 'removed' from the mark-recapture population
for monitoring by telemetry, compared with a lower proportion of 'removal' in the early
(20%) and late ( 17%) fire treatment sites. Using the jackknife population estimate, the
density of C. kingii in the early ftre site, late fire site and the unbumt site were 0.65 ha ·I,
0.78 ha ·I and 0. 1 3 ha ·1, respectively.
103
50
CJ) 40 '1::3 l..... ro N
� 30 � 0 l..... / .\ <D
..c � I \ E 20 ::J I I
z I I 1 0 ? 0 I j \ \ \ I I
b "'--rej � 0 T
J F M A M J J A s 0 N D
Months
Figure 4.5. Mean monthly capture rates of males (circles) and female (squares) frillneck
lizards. All sites and years have been combined.
l04
Table 4 . 1 . Observed and expected capture frequencies, population estimates and "goodness of fit" test for the early fire site.
Number of Number of Poisson Negative Geometric Jackknife estimate captures individuals binomial (95% confidence
intervals)
87 76.9 445.8 82.5
2 25 36.4 129.7 29.3
3 9 11 .5 47.7 10.4
4 3 2.7 19.4 3.7
5 2 0.5 8.3 1.3 6 2 0. 1 3.7 0.5
xz = 9.76 422.21 1 . 46
DF = 2 2
P = 0.007 < 0.0001 0.482
Estimate N = 209 1594 360 279 (212 - 399)
Table 4. 2. Observed and expected capture frequencies, population estimates and "goodness of fit" test for the late fire site.
Number of Number of Poisson Negative Geometric Jackknife estimate captures individuals binomial (95% confidence
intervals)
102 98.2 101.7 102.7
2 3 1 37.3 32.5 30.9
3 l l 9.5 9.3 9.3
4 2 1 .8 2.5 2.8
5 0.27 0.7 0.8
6
xz
=
1 .73 0.41 0.52
DF = 2 2
P = 0.42 0.52 0.77
Estimate N = 278 390 487 314 (245 - 433)
105
Table 4.3. Observed and expected capture frequencies, population estimates for the unburnt site. The "goodness of fit" test was not possible due to the low number of recaptures.
Number of Number of Poisson Negative Geometric Jackknife estimate caprures individuals binomial (95% confidence
intervals)
14 13.5 396.9 13.6
2 2 3 67.5 2.7
3 0.4 14.5 0.5
4
5
6
x.2 = Invalid Invalid Invalid
OF =
P = Estimate N = 48 514 85 66 (27 to 238)
106
From a total of 79 females caught in the three fire treatment sites, none had any evidence
of scars (fresh or old). For adult males, 27% (n = 1 20) were recorded with scars. Analysis
of the proportion of males with scars in four different size classes within this sample
revealed that only 2% of males with an SVL < 225 mm (n = 50) had scarring (Figure 4.6).
The proportion of males with scars increased with increasing SVL (Figure 4.6). The cause
of scars is presumed to be from intraspecific aggression, not predation, as females did not
have any scars. The data suggest that male-male fighting (territorial defense) is greater
among large males. The proportion of scars from each of the three sites was not constant.
No males in the unburnt site had scars. This suggests less interaction among males. Fresh
scarring on adult males was recorded only during the fust months (October to December)
of the reproductive season.
Home ranges
Dry season home ranges are presented in Table 4.4. They represent data from a period of
no greater than six months for each individual lizard. Adult male home ranges during the
dry season were significantly larger than females (males, mean = 1.96 ± 0.57 ha, n = 16;
females, mean = 0.634 ± 0. 1 2 ha, n = 7; t = 2.9, DF = 20, P = 0.009). This suggests either:
( 1 ) adult males require larger home ranges to find more food resources; or (2) adult males
establish larger home ranges to include the maximum number of females. There was no
significant correlation between SVL and home range for either sex (male, r = 0.406, P =
0. 1 18; female, r = 0.488 , P = 0.531). Analysis of differences in home range among the
fire treatment sites was only possible for males, as female sample size was too small.
Although the mean values for both burnt plots were greater than the unburnt plot (early,
mean = 2.9 1 ± 1.08 ha; late, mean = 1 .94 ± 1 .04 ha;
107
1 .0
en .8 (]) ro E
........ .6 :::J /D. "'C / ro / '+- / 0 .4 � 0 c .....-
0 f r..,....- ........-
t !/ 0 a. .2 j/ 0 /I � £l.. _a !
--- I 0.0 ---c..< 0 0 0
1 85 200 225 250
Adult male size classes (mm)
Figure 4.6. Proportion of adult male frillneck lizards with scars for four size classes in each
of the fire treatment sites. Triangles represent the late fire site, squares represent the
early fire site and circles represent the unbumt site.
108
Table 4.4. Dry season borne ranges and movement for telemetered male and female frillneck lizards in each of three fire sites.
Home ranges were calulated using minimum convex polygon. Movement is the mean distance of each location from the geometric centre of each borne range.
Sex SVL Fire Number Movement Home (mm) regune locations (m) range
(ha)
male 250 Early 8 92 0.52
male 260 Early 10 177 8.94
male 250 Early 9 71 0.58
male 250 Early 1 2 63 1.77
male 255 Early 14 69 2.12
male 245 Early 9 83 0.87
male 252 Early 9 92 3.05
male 220 Late 14 85 0.96
male 230 Late 13 80 1.89
male 253 Late 10 15 0.05
male 250 Late 9 147 4.85
male 193 Unburnt 8 43 0.60
male 235 Unbumt 13 57 1.58
male 190 Unbumt 1 1 1 1 0.06
male 245 Unbumt 1 2 36 0.54
male 250 Unbumt 10 5 1 0.54
female 210 Early 9 4 1 0.29
female 197 Early 1 1 26 0.19
female 210 Early 9 5 1 0.37
female 210 Early 10 82 2.55
female 215 Late 10 41 0.35
female 212 Unbumt LO 42 0.63
female 210 Unbumt 10 25 0 . 1 1
109
unburnt. mean = 0.66 ± 0.25 ha), there was no statistical difference in male home ranges
(ANOVA, log10 transformed: F2.16 = 1.29, P = 0.29).
The mean distance of each location from the geometric centre of the home range was
significantly larger for males than females during the dry season (males, mean = 73.27 ±
10.73 m, 11 = 16; females, mean = 43.89 ± 7.26 m, 11 = 7; t = 2.27, P = 0.034). The mean
distance of locations from the geometric centre of individual males home range was large
in both burnt sites compared to the unburnt site (early, mean = 92.49 ± 14.7 m; late, mean
= 8 1.68 ± 27.02 m; unburnt, mean = 39.74 ± 8.01 m). However, there was no significant
difference among fire treaonent sites (F2. 16 = 2.88, P = 0.09).
The analysis of overlap of home range was restricted to individuals monitored concurrently
and located in adjacent areas. Two adult males (SVL >250 mrn) situated approximately 200
m apart were monitored throughout the dry season of 1991 . No overlap between home
ranges occurred during the four months of monitoring. The boundaries of each home range
were separated by a minimum of 30 m. Three telemetered individuals (two adult females
and one adult male) were monitored concurrently during the dry season of 1992. The male
home range overlapped with 27% of one female, but not with the other female. The
female's home range overlapped with 22% of the male's home range. No overlap was
recorded between the two adult females, although they were observed sitting in
neighbouring trees (5 m apart) on one occasion.
1 10
DISCUSSION
The reproductive cycle data presented is similar to that previously reported for C. kingii,
and the pattern is similar to other agamid and iguanid lizards (Shine and Lambeck 1989).
The reproductive season begins before the first rains in October. Importantly, this is when
food availability is relatively low, but the total volume of food in the stomach nevertheless
increases (Chapter 2: Diet). This implies that a greater effort is expended to obtain food
at the same time as reproductive activity begins. Reproduction in C. kingii continues during
the wettest months, until March. The emergence of the majority of hatchlings coincides
with the period of highest food availability (Chapter 2: Food availability) at the end of the
wet season. Thus, hatchlings have approximately two to three months of high food
availability before food resources decrease in the dry season.
The results presented here suggest that most female frillneck lizards reproduce during the
first half of the wet season. However, some females are still gravid during March. This
may represent double clutching within the population, or possibly the sexual maturity of
juvenile females nesting for the first time. Double clutching within a breeding season has
been recorded for C. kingii (Bedford et a!. 1993 ) . Double clutching is common in other
agamid lizards (Dunham et a!. 1988). A late first or second clutch would result in the
emergence of hatchlings at the beginning of the dry season, and this may decrease their
chances of survival. These data also show that the reproductive periodicity of females is
not constant. Apparently, not all females reproduce in each reproductive season, or in
consecutive years. However, it is possible for some adult females to reproduce in
consecutive years, and some adult females may produce two clutches within a single
reproductive season. However, these result may be an artefact of non-continuous sampling
1 1 1
because some females may have had a clutch that was not detected.
Female C. kingii reach sexual maturity at just under two years. The similar sized eastern
water dragon, Physignathus lesueurii, does not reach adult body size until four years
(Thompson 1993). It is not clear whether sexual maturity is reached before the attainment
of adult body size in P. lesueurii, but the growth rate of juvenile C. kingii (7.29 mm
month·1 ) is considerably greater than that of juvenile P. lesueurii (2.25 mm month·1 ). The
difference in juvenile growth between these two large (long-lived) agamid lizards has an
important ecological consequence. By reaching sexual maturity at an earlier age, C. kingii
may have a greater life-time reproductive output compared to P. lesueurii, given that both
are relatively long-lived species (P. lesueurii live to 14 years in captivity) (Thompson
1993). Whether these differences are a result of phylogenetic or environmental conditions
is unclear. Growth in reptiles is influenced by both phylogenetic and biotic factors
(Andrews 1982). The higher ambient temperature and rainfall experienced by C. kingii may
be responsible for increased growth.
However, C. kingii belongs to a different phylogenetic group than P. lesueurii (Witten
1982, Witten 1 983, Greer 1989) which may lead to differences in growth rates. Sexual
maturity in female Pogona barbatus and P. vitticeps occurs in two years (Badham 1 97 1
as cited in Heatwole and Taylor 1987). Although body size is smaller for these two species
compared to Chlamydosaurus and Physignathus, sexual maturity occurs relatively early in
both species of Pogona and in Chlamydosaurus for lizards with a relatively large body
size. It appears that C. kingii has an early-maturing and multiple-brooded life history
strategy. This is consistent with many lizards inhabiting tropical environments (Dunham
1 1 2
et a/. 1988). Bedford et a/. ( 1993) suggest that the reproductive strategy of C. kingii is
similar among the large Australian agamids. The results presented here do not suppon this
generalisation. All lizards in this group have a large body size, i.e. relatively long-lived,
but the Australian evolved agamids may mature markedly earlier than the Asian evolved
spectes.
Dry season fires do not affect the growth rates of male frillneck lizards. This is consistent
with the results on the effect of dry season fires on the diet of C. kingii, in which the
volume of food in the stomach of lizards was similar among all three fire treatments in
both the wet and dry seasons (Chapter 3: Longer-term effects of fire). Therefore, no
differences in growth rates would be expected among populations located relatively close
together and consuming similar amounts of food.
Reponed population densities for the large herbivorous agamid, Uromastyx acanthinurus
(Grenot 1976 as cited in Turner 1 977), are consistent with the density reported here for C.
kingii. The density of the water dragon, P. lesueurii, along riverside habitat, are estimated
to be between 138-2 1 5 lizards per km of river (Thompson 1993). Taking the width of a
river to be 50 m, then this translates to a density of between 2.76 and 4.26 lizards per ha.
This is higher than the density of C. kingii. The continually moist habitat of P. lesueurii
may allow for this greater density. The long dry season in northern Australia, which
reduces the availability of food (Chapter 2: Diet) may be responsible for the difference in
density between these two species.
1 1 3
The density of frillneck lizards was similar between the early and late fire treatments, but
the density of the unbumt site was much lower. All sites were located within 25 km of
each other and all consisted of open Eucalyptus forest. No environmental barriers are
present that would isolate any of the three populations. The low density in the population
of C. kingii in the unbumt site may be attributed to two factors. First, the migration of
frillneck lizards to neighbouring burnt habitat would affect the density. The area adjacent
to the unburnt site was burnt annually, and frillneck lizards were relatively abundant in this
area (pers. obs.). Also, a number of telemetered lizards in the unburnt site moved up to 1
km into the adjacent burnt area. The behaviour of C. kingii moving into recently burnt
habitat is reported in Chapter 3 (Short-term effects of fire). This allows greater accessibility
to food resources in the dry season (Chapter 3: Short-tem1 effects of .fire). Second, the low
reproductive potential of the population in the unburnt site would limit the number of
lizards over the long term. This would also be influenced by the sex ratio being heavily
male biased in the unburnt site. Migration out of the unburnt site may influence the
reproductive potential of this population. It is unclear whether the low density of C. kingii
in the unbumt site is sufficient for the population to sustain itself.
Surprisingly, there was little difference in the size of home range between the dry season
(this study) and the wet season (Shine and Lambeck 1989), for either sex. Home ranges
of females were almost identical between seasons (dry = 0.63 ha, wet = 0.68), and male
home ranges increased in the wet season (dry = 1.96 ha, wet = 2.53 ha). However, adult
male frillneck lizards have larger home ranges than females in the both wet and dry
seasons. There were no difference between sexes in the total volume of food consumed
during the wet and dry seasons (Chapter 2: Diet). Thus, food requirement is not a reason
1 14
for males occupying a larger home range. Males actively defend home ranges during the
wet season (reproductive season) by fighting and the use of displays (Shine 1990). This
behaviour has not been observed in the dry season (non-reproductive season). Larger home
ranges of males in the wet season would presumably enable access to a greater number of
females. The difference in home range between sexes is presumably carried over into the
dry season. If males substantially decreased their home range during the dry season, they
would have to re-establish it during the subsequent wet season (when males become
territorially active). By maintaining a relatively larger home range in the non-reproductive
period, less effort would be required in defense of territories at the beginning of the
reproductive season.
The absence of scars on small males (SVL < 225 mm) indicates that they do not engage
in fighting. This suggests they do not actively defend their home range. Whether small
males are permitted to reside within territories of established large males is not clear. They
may avoid physical confrontation by fleeing from the larger, more aggressive males instead
of engaging in physical confrontations. Observations from mark-recapture censussing
suggests that small adult males can reside within the established home ranges of large adult
males. Also, the absence of scars from males in the unburnt site, where the density of
lizards was extremely low (Figure 4.6), suggests that the lizards at this site do not engage
in combat to defend their home ranges. This is most likely because of the low density of
lizards in this habitat does not allow much interaction between males. Adult females do not
actively defend their home ranges, but it is unclear whether they maintain areas within their
home ranges exclusive from other individuals. Shine ( 1 990) reported a much higher
incidence of male scarring (up to 90%) than in this study. Possible reasons for this
1 1 5
difference are that Shine's ( 1 990) data were collected during the reproductive season.
whereas data presented here were collected throughout the year, or that densities of C.
kingii may have been higher.
Further studies on other large agamids in Australia are needed to further define the
similarities and differences in life history strategies. The absence of population data from
all species within the genus Pogona prohibit comparisons of C. kingii and the other large
agamids which have presumably evolved in Australia. Further, comparisons of populations
of C. kingii from different geographic and climatic locations (temperate and arid) would
increase the understanding of differing environmental conditions and their influence on the
life history of this enigmatic Australia lizard.
Summary
In summary, the reproductive cycle of Chlamydosaurus kingii is associated with the annual
wet season. The lizards begin reproducing prior to the onset of the high food availability
associated with the heavy monsoonal rains. Thus, hatchlings have access to abundant food
resources, prior to the decrease in food during the dry season. Lizards reach sexual
maturity at two years of age, and are relatively long-lived, with some males reaching a
minimum age of six years. Males grow at a faster rate and for a longer period than
females, which relates to the sexual dimorphism in body size. Large differences in densities
occur between habitat unburnt for a number of years and annually burnt habitat. Habitat
preferences for more open ground, and greater access to food over the short-term may be
responsible for these differences. Home ranges differ between sexes in both wet and dry
seasons. This difference is probably due to males maintaining a larger area to assist in the
1 1 6
number of females within their home range, regardless of the time of year. The presence
of scars suggests that only large males defend their home range. But males in the low
density population (unbumt), did not have scars, and this is presumably due to few
encounters between them.
1 17
Chapter 5
Synopsis and management implications.
The frillneck lizard, Chlamydosaurus kingii, through this and other recent studies (Shine
and Lambeck 1 989, Shine 1 990, Christian and Green 1994, Christian and Bedford 1995),
is probably the most well understood of all the terrestrial reptiles of northern Australia.
However, there is still much to learn about this unique and spectacular lizard.
This study provides detailed information on the strategies employed by frillneck lizards to
cope with the annual cycle of a wet-dry climate, coupled with frequent dry season fires.
For example, the strategy of C. kingii to reduce its activity and remain perched in large
trees during the dry season assists in conserving energy during a period of relatively low
food resources. The use of freshly burnt areas to obtain more food, and the tendency to
remain in these burnt areas, suggests that frillneck lizards are able to exploit the
consequences of ftres.
At present, the conservation status of the frillneck lizard in the Northern Territory of
Australia appears secure. The majority of its habitat remains relatively undisturbed by
European settlement. Frequent fires, in the most part, are beneficial in providing increased
access to food in the short-term and maintaining relatively open ground vegetation which
is preferred by frillneck lizards in the long-term. As discussed in Chapter 3, the high
mortality in late dry season fires may pose some long-term problems, but this is dependent
on the frequency and scale of these fues. A recent change (post-European settlement)
towards more frequent late dry season fires has been documented. Relatively small late dry
1 18
season fires would permit recruitment from adjacent areas to occur relatively quickly.
Very large and frequent late dry season fires may decrease the likelihood of sufficient
migration into the middle of these burnt areas. The use of early dry season fires may be
preferable for C. kingii population stability, as these fires offer the advantage of a more
open habitat without high mortality.
Some evidence exists that the frillneck lizard population around the Brisbane area has
decreased in recent years (Wilson and Knowles 1988). The reasons for this decrease are
not documented, but increased urban and rural development may be partly responsible.
Frillneck lizards are common in the backyards and parks in and around Darwin (Northern
Territory). The presence of many native tree species and well watered gardens create a
suitable habitat for the frillneck l izard. The suitability of the urban habitat in and around
Brisbane is not known, and further investigation is suggested to identify the reasons for the
decline of frillneck l izards in that area.
Further research on C. kingii in other climatic parts of its range, and of the other large
Australian agamids, is necessary to better understand the evolutionary relationships in life
history strategies and their environment.
1 1 9
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