Abstract
Positive density-dependent seed and seedling predation, where herbivores selectively eat seeds or seedlings of common species, is thought to play a major role in creating and maintaining plant community diversity. However, many herbivores and seed predators are known to exhibit preferences for rare foods, which could lead to negative density-dependent predation. In this study, we first demonstrate the occurrence of increased predation of locally rare tree species by a widespread group of insular seed and seedling predators, land crabs. We then build computer simulations based on these empirical data to examine the effects of such predation on diversity patterns. Simulations show that herbivore preferences for locally rare species are likely to drive scale-dependent effects on plant community diversity: at small scales these foraging patterns decrease plant community diversity via the selective consumption of rare plant species, while at the landscape level they should increase diversity, at least for short periods, by promoting clustered local dominance of a variety of species. Finally, we compared observed patterns of plant diversity at the site to those obtained via computer simulations, and found that diversity patterns generated under simulations were highly consistent with observed diversity patterns. We posit that preference for rare species by herbivores may be prevalent in low- or moderate-diversity systems, and that these effects may help explain diversity patterns across different spatial scales in such ecosystems.
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Acknowledgments
We thank the National Science Foundation, the National Geographic Society, and Stanford’s Woods Institute for the Environment for their financial support. We also thank the US Fish and Wildlife Service for permission to work in the Palmyra Atoll National Wildlife Refuge. For assistance in the field we are very grateful to L. Anderegg, P. DeSalles, C. Hanson, A. Meyer, A. McInturff, A. Miller-ter Kuile, L. Palumbi, and T.C. Robbins. We thank A. Wegmann for advice and insight throughout. Finally, we thank three anonymous reviewers for their comments, which greatly improved the quality of this manuscript. This is publication number PARC-0092 of the Palmyra Atoll Research Consortium (PARC), and was based on collaboration and networking across multiple partner organizations in PARC, which is supported in part by the National Science Foundation under grant no. 0639185. The experiments comply with the current laws of the country (USA) in which the experiments were performed.
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Communicated by Ines Ibanez.
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Young, H.S., McCauley, D.J., Guevara, R. et al. Consumer preference for seeds and seedlings of rare species impacts tree diversity at multiple scales. Oecologia 172, 857–867 (2013). https://doi.org/10.1007/s00442-012-2542-2
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DOI: https://doi.org/10.1007/s00442-012-2542-2