fine-scale geomorphic pattern and biodiversity duane a. griffin and phil marquis bucknell university...

Fine-scale geomorphic pattern and biodiversity

Duane A. Griffinand Phil Marquis

Bucknell UniversityLewisburg, PA

Plant Biodiversity Patterns

Species Area Effect

1

1.5

2

2.5

3

3.5

4 6 8 10 12

Log A

Lo

g S

SW Australia

UK

Sea of Cortez

Linear (UK)

Linear (Sea ofCortez)Linear (SWAustralia)

Explanations

With Apologies: One More!

• Competitive uncoupling hypothesis

• Fine-scale habitat structure can disrupt interactions between individuals sharing a habitat.

• If interactions are negative (competition, allelopathy, pathogen spread…), fragmentation should disrupt trajectories towards exclusion, thereby increasing diversity.

How does this individual interactwith others in its habitat?

Direct interactions with immediate neighbors (competition)

Seed dispersal and microsite colonization

Direct interactions with immediate neighbors (competition)

Mostly Deterministic

Mostly Stochastic

y = f(x)

What if habitat patches are discrete and isolated at fine scales?

Colonization neighborhood remains the same

Resource competition neighborhood is smaller

y = f(x)

Testing: GeoSim• Individual-Based

• Spatially Explicit

• Reaction-Diffusion Model

Diffusion

Reaction

Seed Dispersal Colonization Lottery

CompetitionSeed Production

ABA

ABA

BAA



8

)αNN(8ΦF jiji

i

8

)αNN(8ΦF ijij

j

1 2 3

4 5 6

7 8 9

Landscapes Habitat Area

0

200

400

600

800

1000

0 1 2 3 4 5 6 7 8 9

Landscape

Cel

ls

Landscape Fragmentation

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6 7 8 9

Landscape

Ag

gre

gat

ion

in

dex

Experiment

• 2 species: “a” & “b”– Asymmetric competition (αab = 10, α ba = 1)

– Symmetric fecundity and dispersal parameters

• 100 runs in each of:– 9 unfragmented landscapes– 9 fragmented landscapes

• Aggregation Index (Landscape statistics: APACK v. 2.23 (Mladenoff and DeZonia 2004)

Results: Area Effect

Null Landscapes (100 Runs)

0

4

8

12

16

20

0 200 400 600 800 1000

Area (Cells)

Mea

n S

p B

TT

E

Results: Time to Extinction

Fragmented Landscapes: 100 Runs

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Aggregation Index

Mea

n S

p B

TT

E/G

rid

Cel

ls

Average

95% CI

Species B Dynamics

0%

20%

40%

60%

80%

0 50 100 150 200

Time Steps

Per

cen

t o

f H

abit

at C

ells

(S

p B

)

Landscape 8: AI = 0.8



Results

Conclusion

Fine-scale habitat fragmentation

facilitates coexistence of

competitively asymmetric

species.

In a digital landscape, at

least.

Does this happen in real landscapes?

Yes.

Carrizozo Malpais: 2 x 50m Transects

y = 0.623x + 9.6283

R2 = 0.6863p<0.01

0

5

10

15

20

25

30

35

40

45

15 25 35 45 55

Fragmentation Index

Sp

ecie

s

Carrizozo Malpais: 2 x 50m Transects

y = 0.623x + 9.6283

R2 = 0.6863p<0.01

0

5

10

15

20

25

30

35

40

45

15 25 35 45 55

Fragmentation Index

Sp

ecie

s

Fragmentation, Diversity, Space, and Time

• Fragmentation disrupts the processes governing membership in ecological communities.– Negatively– Positively

• Allopatric speciation• Competitive uncoupling (?)

Space

Tim

e

+Uncoupling

+Allopatric speciation

Fragmentation, Diversity, Space, and Time

+“Spatial insurance”(Metapopulations)

−Habitat fragmentation → relaxation

− ?

Might Uncoupling Emerge at Broader Scales?

Some Implications

• Rare species may gain refuge in habitats with fine-scale fragmentation.

• Habitats with fine-scale fragmentation may provide immigration points for exotic species.

• It’s worth looking into this…

Acknowledgements

• Office of the President, Bucknell University

• Office of the Dean, Bucknell University College of Arts and Sciences

• Bryn Scriver and John Stoddard

Thank you.

fine-scale geomorphic pattern and biodiversity duane a. griffin and phil marquis bucknell university...

Documents