ESA 2011 Austin, TX

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Text of ESA 2011 Austin, TX

  • 1. Spatial variability in granivory determines the strength of stochastic community assembly Rachel M. Germain1*, Laura Johnson1, Andrew MacDougall1, Karl Cottenie1, and Elizabeth Gillis21Department of Integrative Biology, University of Guelph, ON; 2Department of Resource Management, Vancouver Island University, BC
  • 2. 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)
  • 3. 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 False dichotomy?(Adler et al. 2007; Chase 2007, 2010)
  • 4. Evaluating assembly processes with -diversity Stochastic Deterministic -diversity is high -diversity is low Regional scale Local scale Species
  • 5. Stochasticity increases with productivity in experimental pond communities (from Chase 2010 Science)
  • 6. 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)
  • 7. Small mammal impacts on tallgrass prairie assembly1. 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?
  • 8. Charitable research reserveCambridge, ON, CA
  • 9. Prairie restorationPloughed and seeded with 24native tallgrass prairie speciesSeeds randomly applied using atracker-drawn seeder
  • 10. Small mammal impacts on tallgrass prairie assembly1. Are small mammals agents of deterministic assembly? Prediction: small mammals will selectively remove some species over others2. Are small mammal effects spatially predictable?3. Do small mammals alter the trajectory of native plant assembly ?
  • 11. 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
  • 12. Forb seeds were removed significantly more than shrub and grass seeds Forbs Shrubs Grasses 10 8Seeds remaining 6 4 2 0 Functional group: F2,23 = 29.97, P < 0.001* Seed species Species: F5,23 = 0.35, P = 0.876
  • 13. Small mammal impacts on tallgrass prairie assembly1. Are small mammals agents of deterministic assembly?2. Are small mammal effects spatially predictable? Prediction: Seed removal will decrease with distance from the prairie edge3. Do small mammals alter the trajectory of native plant assembly?
  • 14. 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
  • 15. Seed removal was strongest in the old-field, and decreased with distance from the edge Closed Open prairie old-field Seeds removed (log10) -30 -10 10 30 50 70 90+ Distance from edge (m) F1,84 = 150.9, P < 0.0001*
  • 16. Small mammal impacts on tallgrass prairie assembly1. 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: - and -diversity will increase with distance from the prairie edge where small mammals are less abundant
  • 17. 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: : species per plot ~ distance from edge : Jaccards dissimilarity ~ distance from edge Heliopsis Solidago Desmodium Ratibida
  • 18. - and -diversity increased with distance from the edge of the prairie F1,48 = 12.82, P