© sser ltd.. ecological techniques a variety of universal practical approaches exist for...
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© SSER Ltd.
Ecological Techniques
A variety of universal practical approachesexist for investigating the biotic and abiotic
components of ecosystems
Field ecologists investigate communities by using random sampling techniques that aim to:
• eliminate bias• reduce the effects of chance• minimise errors in obtaining
measurements/samples
Quadrat and transect sampling are commonly used methods for investigating distribution within plant communities and the more sedentary populations of animals such as those found inhabiting seashores
Let’s pretend we’re Ecologists…
Sunflower LAB!
Quadrats
Frame quadrats are wooden or metal frames of known area (e.g. 0.25 m2, 0.5 m2, 1.0 m2) and are generally square-shaped
Various approaches are used to determine the representation of species within an area:
• Species population density (number of individuals per square metre) is determined by counting all individuals within a series of randomly placed quadrat frames and calculating the mean
• Percentage cover is determined subjectively by assessing the extent to which different species occupy subdivided quadrat frames OR by the use of point quadrat frames
• Frequency of occurrence of a species is determined using subdivided quadrats and point quadrat frames
Quadrats
Square quadrat framefor determining
population densities
Subdivided quadrat framefor determining % cover
of species
Quadrat frames, constructed from wood or metal, are used to investigate the distribution of species
Point QuadratFrame
Metal pins are dropped through each hole in turn and ‘hits’ are recorded
No. of hits% Cover = ------------------- x 100
Total no. of pins
Random Sampling
The validity of results obtained from the various sampling methods is dependent upon the adoption of random sampling techniques
Strategies for avoiding bias through random sampling utilise a number of approaches – these include random
sampling using a grid
A grid is created by laying out tapes at right angles to one another to form the axes of the gridded area
Pairs of random numbers are used to provide the coordinates for locating quadrats
Tapes are laid out at right anglesto one another and form the axes
for locating quadrats(the size of the grid depends upon
the area being investigated)
Pairs of random numbers are generated on a calculator or
computer and used as coordinatesfor the location of quadrats
09 12 14 07 11 11
06 03 01 05 03 10
14 03 07 02 15 00
03 07 00 05 10 14
00 13 04 14 01 14
Using Random Numbers
Pairs of random numbers are selectedby reading across or down the table in any
direction e.g. X09 Y12, X14 Y07, etc. or X09 Y06, X14 Y03 etc.
Many random number pairs are needed forlarge grids
09 12 14 07 11 11 04 02 11 03
06 03 01 05 03 10 06 02 02 10
14 03 07 02 15 00 09 06 04 11
03 07 00 05 10 14 15 06 11 00
00 13 04 14 01 14 06 03 14 12
12 05 02 03 06 05 08 03 07 01
08 04 09 05 06 04 06 14 12 13
10 01 14 06 09 07 10 11 13 03
14 02 00 10 12 00 13 06 11 10
04 02 11 01 02 11 03 01 07 03
15 15 10 09 05 00 13 08 13 01
14 14 01 01 02 09 05 01 08 15
06 02 15 11 02 11 11 04 05 07
07 05 07 06 09 04 07 00 07 03
14 10 03 06 11 07 13 11 13 12
13 11 13 08 12 07 03 09 11 11
02 01 01 04 12 03 03 02 03 06
14 07 00 00 13 08 14 12 10 11
00 09 01 13 12 11 05 00 00 04
07 03 02 11 15 13 01 05 12 10
10 02 12 05 08 13 06 06 09 11
06 05 07 06 14 04 10 00 03 12
07 12 04 14 10 02 14 04 04 13
01 11 05 11 06 14 06 15 04 01
01 04 05 02 07 13 09 13 08 06
03 09 01 02 02 15 09 09 07 07
06 13 11 05 15 07 11 03 06 07
12 05 03 04 14 06 14 04 04 04
12 06 02 05 04 15 03 09 09 05
05 15 03 10 09 02 03 10 14 05
14 11 14 08 06 03 07 04 13 15
06 03 15 08 11 01 01 13 04 04
05 12 02 11 09 11 11 01 02 00
13 11 15 11 11 09 12 08 12 05
07 13 13 09 00 14 11 13 06 04
09 14 15 07 14 08 05 04 14 12
03 11 12 15 10 15 15 06 13 10
15 08 11 06 05 15 09 05 01 08
This quadrat has coordinates X09, Y06
Transects
A transect is a line, created with string or a tape, along which systematic sampling
is performedTransects are particularly useful for sampling areas
where there is a transition of species from one habitat to another as environmental conditions change
Transect studies are used to investigate gradients such as zonation on rocky shores and changes in the species
diversity across sand dunes
A line transect is one in which all individual organisms touching the tape/string are recorded
The most commonly used belt transect involves laying a tape through the area of study and sampling the
population with quadrats positioned at regular intervals alongside the tape
Belt transect Surveyof a Dune System
A belt transect was used to investigate the distribution of three species of grass commonly found on sand dunes
The transect line stretched from the High Water Mark to the inland area and 1m x 1m quadrats were used to
determine the number of individual plants of each grass species along the profile
Number of plants/m2 Distance inland from High
Water Mark (m) Sand couch grass
Marram grass Sand Fescue
0-5 3
5-10 8
10-15 27
15-20 6 3
20-25 6
25-30 38
30-35 29
35-40 15
40-45 8 17
45-50 48
50-55 88
55-60 97
Present the results as a bar chart
0
10
20
30
40
50
60
70
80
90
100
0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60
Distance from high water mark (m)
Nu
mb
er o
f p
lan
ts p
er m
2
Sand couch grass
Marram grass
Sand fescue
Random Sampling Using A Grid
The students used aerial photographs of the two fields to compare the dandelion populations
(photographs provided in the workbook)
A 15 cm x 15 cm square was drawn around each field photograph and divided up into 1 cm squares
The X-axis was drawn along the bottom of the photograph with the Y-axis on the left hand side
Random number tables were used to provide coordinates for locating quadrat positions
Quadrat positions were identified by treating the crossing coordinate lines as the lower left-hand corner
of each quadrat
Thirty DIFFERENT coordinates were used to locate quadrats and the number of dandelions in each quadratwas recorded (the north west rule was applied to ensure
that no individual was counted twice)
Exercise – A Tale of Two Fields
Use the photographs provided in the workbook to create 15 cm x 15 cm grids for the two fields
Using the provided random numbers table, count and record the number of dandelions in 30 randomly
located quadrats for each field
Calculate the mean number of dandelions for each field
State a Null and Alternative Hypothesisfor the investigation
Test the statistical significance of any differences between the two datasets using the Mann-Whitney U
Test for non-normal data
Provide an explanation for any differences that you find between the grazed field (Field 1) and
the hay field (Field 2)
The capture-mark-recapture technique can be used to estimate
the population size of mobile organisms, such as woodlice
• Organisms are captured using an appropriate technique (pitfall traps, sticky traps, etc)
• Captured organisms are marked with non-toxic waterproof paint
• Marked organisms are released back into the environment
• After a suitable period of time, the population is sampled again
• The number of marked and unmarked organisms in the second sample is recorded
Estimating The Population Size
Data obtained from the capture-mark-recapture technique is used to calculate an
estimate of population size using the following equation:
number of organisms number of organisms in first sample x in second samplePopulation size (P) = ------------------------------------------------------
number of markedindividuals captured
Example:In an investigation into woodland habitats, 42 woodlice were caught, marked and released. Two days later 40
woodlice were caught of which 8 were found to be marked.Estimate the size of the woodlouse population
Estimating The Population Size
number of organisms number of organisms in first sample x in second samplePopulation size (P) = ------------------------------------------------------
number of markedindividuals captured
This calculation is only valid if certain assumptions about the sampled population hold
42 x 40Population size (P) = ------------------------------------ = 210
8
Estimating The Population Size
Assumptions
• Marking should not disadvantage individuals in any way, e.g. making organisms more visible to predators
• Marked individuals are assumed to mix completely back into the original population
• There should be no immigration or emigration of individuals between sampling periods, i.e. the population is closed
• It is assumed that there are no births or deaths during the period of the study
The Theory of Lincoln…
• In theory, mark / recapture techniques involve sampling a population of animals and then marking all of the individuals captured in a recognizable way. The marked animals are then released back into the population and left to mingle for a suitable period of time. Once they have become thoroughly mixed into the population again, the population is resampled.
• The assumption is then made that the proportion of marked animals in the second sample is the same as the proportion of marked animals to non-marked within the whole population. Enough time must be allowed to elapse for complete mixing to have occurred.
Acknowledgements
Copyright ©2003 SSER Ltd. and its licensors.All rights reserved.
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