1. Coexistence patterns in a desert rodent community The relative importance of stabilizing mechanisms of coexistence Glenda Yenni Department of Biology, Ecology Center Department of Math and Statistics Utah State University 2009 Annual Meeting of the American Society of Mammalogists, University of Alaska Fairbanks

2. Negative frequency dependence in growth rates Enable species to increase when rare Indication of stabilizing mechanisms of coexistence (Chesson 2000, ‘niches’) Empirical evidence in pair- wise interactions A Niche for Neutrality, Adler et al 2007

3. Multi-species dominance and stabilization Fo Fo = 0.2 S = -2 Fo = 0.6 S = -2 Fo = 0.15 S = -2 Fo = 0.15 S = -4

4. Portal LTREB Chihuahuan desert Since 1977 20 ha, 24 plots  10 controls – equal access  8 k-rat (Dipodomys) exclosures  6 total rodent exclosures Abundance, community E use

5. Portal LTREB p=0.001, p=0.0004, p=0.004, p=0.007 p=0.000, p=0.03

6. Sevilleta LTER p=0.0001, p=0.02, p=0.02 p=0.03, p=0.003 p=0.01

7. Coexistence A Niche for Neutrality, Adler et al 2007

8. Coexistence predictions + + + + + + + + + + + + + + + + + ++ + + + + + + + + + + + + + +/- relationship btw strength of stabilization and mean population abundance Stable coexistence Competitive exclusion + + + -- Strength of stabilization Fitness equivalence

9. Deterministic coexistence + positive relationship btw strength of stabilization and mean population abundance - negative relationship btw strength of stabilization and mean population abundance +/- coexistence +/- competitive exclusion/stochastic extinction

10. Stochastic coexistence + positive relationship btw strength of stabilization and mean population abundance - negative relationship btw strength of stabilization and mean population abundance +/- coexistence +/- competitive exclusion/stochastic extinction

11. Implications/ Future Directions Rare species benefit from stronger negative frequency-dependence more than dominant species  Strong stabilizing mechanisms aid persistence of non- dominants in variable communities Implications for the ability of changing regions (via invasive species, climate change) to maintain species richness Explore entire coexistence space Apply to other coexistence models

12. Acknowledgments Morgan Ernest for advising and support Peter Adler, Xiao Xiao Kate Thibault, Sarah Mohlman, and other past and future fellow Portal RAs Selected Professions Fellowship, AAUW The Portal project is currently supported by NSF grant DEB- 0702875 Questions?