ESA 2011 Austin, TX
description
Transcript of ESA 2011 Austin, TX
Spatial variability in granivory determines the strength of stochastic community assemblyRachel M. Germain1*, Laura Johnson1, Andrew MacDougall1, Karl Cottenie1, and Elizabeth Gillis2
1Department of Integrative Biology, University of Guelph, ON; 2Department of Resource Management, Vancouver Island University, BC
What structures diversity?
• Neutral-based stochastic perspective:– species are functionally equivalent– ecological drift and dispersal
• Niche-based deterministic perspective:– species are functionally distinct– biotic and abiotic interactions
(Adler et al. 2007; Chase 2007, 2010)
What structures diversity?
• Neutral-based stochastic perspective:– species are functionally equivalent– ecological drift and dispersal
• Niche-based deterministic perspective:– species are functionally distinct– biotic and abiotic interactions
(Adler et al. 2007; Chase 2007, 2010) False dichotomy?
Evaluating assembly processes withβ-diversity
Stochastic
β-diversity is high
Deterministic
β-diversity is low
Regional scale Local scale Species
Stochasticity increases with productivity in experimental pond communities
(from Chase 2010 Science)
Small mammals regulate plant community assembly
• Populations are rapidly increasing
• Selective foragers
• Habitat use is spatially predictable– predator risk– distance from nesting sites
(Kotler 1984; Howe et al. 2006)
Small mammal impacts on tallgrass prairie assembly
1. Are small mammals agents of deterministic assembly?
2. Are small mammal effects spatially predictable?
3. Do small mammals alter the trajectory of native plant assembly?
Charitable research reserveCambridge, ON, CA
Prairie restoration
Ploughed and seeded with 24 native tallgrass prairie species
Seeds randomly applied using a tracker-drawn seeder
1. Are small mammals agents of deterministic assembly?
2. Are small mammal effects spatially predictable?
3. Do small mammals alter the trajectory of native plant assembly ?
Small mammal impacts on tallgrass prairie assembly
• Prediction: small mammals will selectively remove some species over others
Cafeteria trial• For each of 8 seed species, we prepared 8 dishes of 10 seeds
• Half of the dishes per species were covered by wire mesh (control)
• Seeds counted after 24 hours in the field
• Analysis:
– nested ANOVA: seeds remaining ~ functional group + seed species
H. annus
H. dive
ricatus
L. ca
pitata
R. blanda
S. tri
folia
S. cry
ptandrus
B. inerm
is
B. kalm
ii0
2
4
6
8
10
Seed species
Seed
s re
mai
ning
Forb seeds were removed significantly more than shrub and grass seeds
Functional group: F2,23 = 29.97, P < 0.001*Species: F5,23 = 0.35, P = 0.876
Forbs Shrubs Grasses
Small mammal impacts on tallgrass prairie assembly
1. Are small mammals agents of deterministic assembly?
2. Are small mammal effects spatially predictable?
3. Do small mammals alter the trajectory of native plant assembly?
• Prediction: Seed removal will decrease with distance from the prairie edge
Small mammal survey• Conducted in mid-April
• Samples of 10 sunflower seeds on bare soil at 100 random locations across our site
• Seeds counted after 14 days in the field
• Analysis:– ANOVA: seed removal ~ distance from edge
Closedold-field Open prairie
-30 -10 10 30 50 70 90+
Distance from edge (m)
Seed
s re
mov
ed (l
og10
)
Seed removal was strongest in the old-field, and decreased with distance from the edge
F1,84 = 150.9, P < 0.0001*
Small mammal impacts on tallgrass prairie assembly
1. Are small mammals agents of deterministic assembly?
2. Are small mammal effects spatially predictable?
3. Do small mammals alter the trajectory of native plant assembly ?
• Prediction: α- and β-diversity will increase with distance from the prairie edge where small mammals are less abundant
Community-wide diversity survey
• We surveyed fifty 5 x 5 m plots at random locations across our study site
• Presence/absence data for all species• Analysis:
– α: species per plot ~ distance from edge– β: Jaccard’s dissimilarity ~ distance from edge
Heliopsis Solidago Desmodium Ratibida
α- and β-diversity increased with distance from the edge of the prairie
P = 0.012*F1,48 = 12.82, P <0.001*
β-di
vers
ity (J
acca
rd’s
diss
imila
rity)
α-d
iver
sity
(spe
cies
per
plo
t) α β
Role of granivory during tallgrass prairie assembly
1. Forb seeds were removed significantly more than shrub and grass seeds
2. Small mammal impacts were strongest in the adjacent old-field, and decreased with distance from the prairie edge
3. α- and β-diversity increased along a prairie edge-to-interior gradient
oldfield
increasingβ-diversity
decreasing seed
predation
Deterministic assembly
Stochastic assembly
Net effect: fine-scale switching in the strength of assembly processes
prairie interior
oldfield
increasingβ-diversity
decreasing seed
predation
Deterministic assembly
Stochastic assembly
Net effect: fine-scale switching in the strength of assembly processes
prairie interior
oldfield
increasingβ-diversity
decreasing seed
predation
Deterministic assembly
Stochastic assembly
Net effect: fine-scale switching in the strength of assembly processes
prairie interior
Acknowledgements
Carole Ann LeCroix for assistance with plant identification
Mathis Natvik for seeding the field
Peter Kelly--coordinator of the rare charitable research reserve
NSERC and CFI Infrastructure grants