correlations between functional traits, environmental ... · correlations between functional...

Correlations between functional traits, environmental gradients, and distributional

patterns of vascular epiphytes within tropical canopies in Costa Rica

Carrie L. Woods, Ph.D candidate

Clemson University

ATBC 2013

1

• A central question in community ecology concerns the number of species able to coexist at small spatial scales (a diversity)

• High in tropical forests

Diversity

2

Introduction Methods Results Conclusion

Valencia et al. 1994, Woods et al. in prep

• Habitat heterogeneity promotes species diversity

• Structurally complex environments enable habitat partitioning

Diversity

3


(Hutchinson 1959, MacArthur 1958, MacArthur and MacArthur 1961, Ricklefs 1977, Huston 1979, Tilman 1986, Rosenzweig 1995)

“Heterogeneity matters”, Deborah Clark, ATBC 2013

• Relates the function of a plant to the environment

– Resource allocation

– Trade offs

– e.g. leaf thickness

• Enables a better prediction and understanding of the distribution and coexistence of species

Functional traits

4


Westoby et al. 2002, Wright et al. 2004

Questions

• Do epiphytes partition the canopy along habitat and resource gradients?

• Do functional leaf traits explain the distribution of epiphytes within tree canopies?

5


Habitat diversity in the canopy

• Structurally complex

• Habitat gradients (temperature, RH wind speed, branch diameter)

• Resource gradients (canopy soil, atmosphere, light)

6

Resource diversity

Light Canopy soil

Habitat diversity

temperature, wind

RH Branch diameter

Atmosphere

(Parker 1995, Nadkarni 2004)

• Multiple adaptations to take up water and nutrients

Vascular epiphytes: Functional complexity

7

Canopy soil Water from tanks

Aerial roots Atmospheric uptake

Soil ferns Aroids, Orchids Tank bromeliads Atmospheric bromeliads Bark Ferns?


Vascular epiphytes: Functional complexity

8


Habitat partitioning of canopy by epiphytes

9


• Habitat partitioning

– Pittendrigh 1948

– Benzing and Renfrow 1971

– Johansson 1974

– Hietz and Briones 1998

– Zotz et al 2007

– Reyes-García 2012

• Habitat specialization?

Field site

• La Selva Biological Research Station in Costa Rica

• Wet tropical forest

• 4000 mm of annual precipitation

• Average monthly temperature is 25.8°C ± 0.2, and varies little throughout the year

10


• 5 emergent Virola koschnyi trees

– 90° branches and no trunk epiphytes

• Spatial distribution of epiphytes every meter (m)

Data collection methods

11


• Habitat gradients

– T, RH, vapor pressure deficit (VPD)

– Branch diameter

• Resource gradients

– % canopy openness (light)

– % canopy soil cover

Data collection methods

12

T/RH datalogger


13

Inner canopy 0-2 m from trunk

Canopy zones: Inner (0-2 m) Introduction Methods Results Conclusion

Canopy zones: Mid (2-5 m)

14

Mid canopy 2-5 m from the trunk


15

Canopy zones: Outer (> 5 m)

Outer canopy > 5 m from the trunk


16

Habitat associations Introduction Methods Results Conclusion

• Conservative randomization tests for epiphyte species associations for each canopy zone

• Compared the ObsRelDen of each species to the ExpRelDen generated by 1000 iterations of random shuffling the 3 canopy zones (two tailed test, a = 0.05)

• Obs > Exp 97.5% = positive

• Obs < Exp 97.5% = negative DeWalt et al. 2006

Functional leaf traits

17

• Functional leaf traits of abundant epiphyte species within Virola koschnyi trees

– 10 individual leaves per species

– No orchids or atmospheric bromeliads

– Soil ferns, Aroids, Tank bromeliads, and Bark ferns

• Examined relationships between habitat and resource gradients and functional leaf traits


Functional leaf traits

18


• Environmental conditions – Air VPD

– Substrate temperature

– % canopy openness

• Functional leaf traits – Specific leaf area (SLA)

– Leaf dry matter content (LDMC)

– Succulence

– Sclerophylly

– Leaf toughness (LTo)

– Rate of epidermal water loss (EWL)

T/RH datalogger

Leaf penetrometer

19

Habitat and Resource gradients: canopy zones Introduction Methods Results Conclusion

Inner (0-2 m) Mid (2-5 m) Outer (> 5 m)

% c

an

op

y s

oil

co

ve

r

0

20

40

60

80

100


Bra

nch d

iam

ete

r (c

m)

0

5

10

15

20

25

30 a

b

c

a

b

c


% c

anopy o

penn

ess

0

10

20

30

40

50

60

a

b

c


VP

D (

kP

a)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

a ab

b

Are different species associated with these diverse habitats?

Woods et al. in prep

20

Habitat partitioning of canopy zones

Soil ferns Aroids

Tank bromeliads

Orchids

Atmospheric bromeliads

Bark ferns

Inner + Mid Outer

All zones Low VPD, low % CO, soil



21

Soil ferns Aroids

Tank bromeliads

Orchids


Bark ferns

Inner + Mid Outer

All zones

Habitat partitioning of canopy zones

Low VPD, low % CO, soil High VPD, high % CO, bark



22

Soil ferns Aroids

Tank bromeliads

Orchids


Bark ferns

Inner + Mid Outer

All zones

Habitat partitioning of canopy zones Introduction Methods Results Conclusion

Low VPD, low % CO, soil High VPD, high % CO, bark

What mechanisms underlie this pattern?


23

Trait-Environment Relationships Introduction Methods Results Conclusion

PCA1-4 -2 0 2 4

PC

A2

-4

-2

0

2

4

substrate

temperature

CO

RH

air temperature

VPD

SLA

Sclerophylly

LDMC

Leaf thickness

Succulence

L

eaf

tou

gh

ne

ss

Le

af

res

ista

nc

e t

o f

rac

ture

R

ate

of

EW

L

PC

A2

-4

-2

0

2

4

ElaLatElaLat

AntUpa GuzLinGuzLin

GuzLinGuzLin

AntUpa

GuzLin

GuzLin

TilAnc

TilAnc

TilAncTilAnc

TilAnc

TilAnc

TilAnc

AecNud

GuzMonGuzMon

AecNud GuzLinGuzLin

TilAnc

TilAncTilAnc

AntUpaElaLat

GuzLinGuzLin

ElaHerElaHer

AntUpa

AntRam

TilMonTilMonTilMon

TilMon

TilMon

TilMon

ElaHer

GuzMonGuzMon

AntUpaAntUpa

TilMon

TilMonTilMon

MicRep

MicRep

MicRep

MicRep

MicRep

MicRepMicRepMicRep

MicRep

MicRep

ElaLat

AntRam

ElaLat

ElaHer

ElaHerElaHer

ElaHer

ElaHer

AntRamAntRam

ElaHer

ElaHer

AecNudAecNud

AecNudAecNud

AecNudAecNud

AecNud

AntRam

AntRamAntUpa

AntUpa

ElaLat

AntUpa

ElaLat GuzMon

GuzMon

substrate

temperature

CO

RH

air temperature

VPD

(A)

(B)

Soil ferns Aroids Tank bromeliads Bark ferns

PCA1 (39.9%)

PC

A2

(2

3.0

%)

24

Functional leaf traits of functional groups Introduction Methods Results Conclusion

SL

A (

mm

2 m

g-1

)

0

4

8

12

16

20

aa

b

b

Scle

roph

ylly

(g m

-2)

40

80

120

160

200

240

a

a

b

b

Soil fern

Aroid

Tank bromeliad

Bark fern

LD

MC

(m

g g

-1)

100

150

200

250

300

350 a

b

cc

Soil fern

Aroid

Tank bromeliad

Bark fern

Su

ccu

len

ce

(g m

m-2

)

300

400

500

600

700

a

b

a

a

25

Habitat partitioning based on functional traits

PCA1

-4 -2 0 2 4

Soil fern

Aroid

Tank bromeliad

Bark fern

PCA1

-4 -2 0 2 4

ElaHer

ElaLat

AntUpa

AntRam

AecNud

TilAnc

GuzMon

GuzLin

TilMon

MicRep

(A)

(C)

-4 -2 0 2 4

PCA2

-4 -2 0 2 4

(B)

(D)

Bark ferns

Tank bromeliads

Aroids

Soil ferns

PCA1

Soil ferns and aroids

– shady sites with high RH and low VPD

– Large investment in leaf structure

Most tank bromeliads and bark ferns

– More open and hot sites with high VPD

– Low investment in leaf structure


PCA1-4 -2 0 2 4

PC

A2

-4

-2

0

2

4

substrate

temperature

CO

RH

air temperature

VPD

SLA

Sclerophylly

LDMC

Leaf thickness

Succulence

L

eaf

tou

gh

ne

ss

Le

af

res

ista

nc

e t

o f

rac

ture

R

ate

of

EW

L

PC

A2

-4

-2

0

2

4

ElaLatElaLat

AntUpa GuzLinGuzLin

GuzLinGuzLin

AntUpa

GuzLin

GuzLin

TilAnc

TilAnc

TilAncTilAnc

TilAnc

TilAnc

TilAnc

AecNud

GuzMonGuzMon

AecNud GuzLinGuzLin

TilAnc

TilAncTilAnc

AntUpaElaLat

GuzLinGuzLin

ElaHerElaHer

AntUpa

AntRam

TilMonTilMonTilMon

TilMon

TilMon

TilMon

ElaHer

GuzMonGuzMon

AntUpaAntUpa

TilMon

TilMonTilMon

MicRep

MicRep

MicRep

MicRep

MicRep

MicRepMicRepMicRep

MicRep

MicRep

ElaLat

AntRam

ElaLat

ElaHer

ElaHerElaHer

ElaHer

ElaHer

AntRamAntRam

ElaHer

ElaHer

AecNudAecNud

AecNudAecNud

AecNudAecNud

AecNud

AntRam

AntRamAntUpa

AntUpa

ElaLat

AntUpa

ElaLat GuzMon

GuzMon

substrate

temperature

CO

RH

air temperature

VPD

(A)

(B)

Functional strategies explain partitioning

26

• Specialization to particular habitats based on functional leaf traits (niche partitioning)

• Different species and functional groups converged on a similar strategy when in a similar habitat

• Functional leaf traits explained the distribution of epiphytes within tree canopies


Acknowledgements

Ralph Garcia, Minor Hidalgo, Angie Amesquita (REU), Sarah Callan, and Dr. Saara J. DeWalt (advisor)

Dr. Catherine Cardelús Rigoberto Vargas Carly Phillips Lindsay Martin

27

http://www.ots.ac.cr/

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