Abstract
Previous island biogeography studies have quantified species richness on the scale of entire islands rather than smaller scales relevant to plant-to-plant competitive interactions. Further, they have not accounted for density compensation. Using mainland and island sites along the New England coast, we asked two questions. First, are both richness and density lower in small-scale habitats within islands than in similar mainland habitats? Second, do differences in competitor richness and density drive post-establishment trait variation in nonnative plant species? We used field surveys and individual-based rarefaction to estimate richness and density in 100-m2 plots and demonstrated that island sites have significantly fewer species and individuals per unit area than mainland sites. We then conducted a field study in which we removed competing neighbors from nonnative plant individuals and found that when competitors were removed, individuals in low-competition environments demonstrated a lesser increase in vegetative growth but a greater increase in reproductive effort and herbivore tolerance relative to mainland individuals whose neighbors were also removed. We found that the central concept of island biogeography, i.e., that islands host fewer species than comparable mainland habitats, can be extended to smaller-scale habitats and that this difference in competitive pressure between mainland and island habitats can act as a driver of trait variation in nonnative plants.
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Acknowledgments
We thank two anonymous reviewers for their comments on an early draft. We thank E. Farnsworth, P. August, and K. Killingbeck (URI) for guidance in developing the experimental designs utilized in this research and for comments on early drafts. We thank P. August for creating a map of field sites. We thank K. Confreda (URI Coastal Fellows Program), E. Steinauer (Nantucket Biodiversity Initiative, NBI), S Comings (The Nature Conservancy), L. Richards (Peaks Island Land Preserve), B. Howe, D. Atwood, and N. Wilson for field assistance. For site access we thank NBI, the Block Island Conservancy, the towns of Charlestown and North Kingstown, RI, Beverly, MA, and Portland, ME, M. Preston, N. Earnest, J. Robinson, and M. Doughty. Funding was provided by NBI, a National Science Foundation (NSF) Graduate Research Fellowship to JPA, and an NSF grant (IGERT 0504103) to P. August, URI Coastal Institute Integrative Graduate Education and Research Traineeship (IGERT) Program.
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Atwood, J.P., Meyerson, L.A. Island biogeography extends to small-scale habitats: low competitor density and richness on islands may drive trait variation in nonnative plants. Biol Invasions 13, 2035–2043 (2011). https://doi.org/10.1007/s10530-011-0019-6
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DOI: https://doi.org/10.1007/s10530-011-0019-6