Reductions in community evenness can lead to local extinctions as dominant species exclude subordinate species; however, herbivores can prevent competitive exclusion by consuming otherwise dominant plant species, thus increasing evenness. While these predictions logically result from chronic, gradual reductions in evenness, rapid, temporary pulses of dominance may also reduce species richness. Short pulses of dominance can occur as biotic or abiotic conditions temporarily favour one or a few species, manifested as increased temporal variability (the inverse of temporal stability) in community evenness. Here, we tested whether consumers help maintain plant diversity by reducing the temporal variability in community evenness. We tested our hypothesis by reducing herbivore abundance in a detailed study of a developing, tallgrass prairie restoration. To assess the broader implications of the importance of herbivory on community evenness as well as potential mechanisms, we paired this study with a global herbivore reduction experiment. We found that herbivores maintained plant richness in a tallgrass prairie restoration by limiting temporary pulses in dominance by a single species. Dominance by an annual species in a single year was negatively associated with species richness, suggesting that short pulses of dominance may be sufficient to exclude subordinate species. The generality of this site-level relationship was supported by the global experiment in which inter-annual variability in evenness declined in the presence of vertebrate herbivores over timeframes ranging in length from 2 to 5 years, preventing declines in species richness. Furthermore, inter-annual variability of community evenness was also negatively associated with pre-treatment species richness. Synthesis. A loss or reduction of herbivores can destabilize plant communities by allowing brief periods of dominance by one or a few species, potentially triggering a feedback cycle of dominance and extinction. Such cycles may not occur immediately following the loss of herbivores, being delayed until conditions allow temporary periods of dominance by a subset of plant species.
Bibliographical noteFunding Information:
Iowa Living Roadway Trust Fund, Grant/Award Number: 90-00-LRTF-211, 90-00-LRTF-306 and 90-00-LRTF-307; TogetherGreen; ISU Department of EEOB; National Science Foundation, Grant/Award Number: NSF-DEB-1042132, NSF-DEB-1234162 and DG-0001-13; Institute on the Environment
Funding for the restoration experiment was provided by the Iowa Living Roadway Trust Fund project numbers: 90-00-LRTF-211, 90-00-LRTF-306, 90-00-LRTF-307; TogetherGreen; and the ISU Department of EEOB. A. Zhang, J. Bickley, T. Luesink and L. Sullivan assisted in data collection; and E. Bach, L. Biederman, J. Doudna, C. Duthie, T. Flick, H. Frater, P. Frater, J. Gallagher, M. Karnatz, L. Martin, L. Sullivan and R. Williams assisted with the restoration. The Nutrient Network (http://www.nutnet.org) experiment is funded at the site-scale by individual researchers too numerous to thank here, but not in the supporting information (see Table S7). Coordination and data management have been supported by funding to E. Borer and E. Seabloom from the National Science Foundation Research Coordination Network (NSF-DEB-1042132) and Long Term Ecological Research (NSF-DEB-1234162 to Cedar Creek LTER) programs, and the Institute on the Environment (DG-0001-13). We also thank the Minnesota Supercomputer Institute for hosting project data and the Institute on the Environment for hosting Network meetings. The authors declare no conflict of interest.
© 2017 The Authors. Journal of Ecology © 2017 British Ecological Society
- Chamaecrista fasciculata
- determinants of plant community diversity and structure
- nutrient network
- plant–herbivore interactions
- plant–plant interactions