Tuesday, June 5, 2012

Contextual evolution on islands

On islands, large mammals get small and small mammals get large. However, there are many exceptions with a lot of scatter around the general, graded trend. So what with the island rule? What causes these deviations? Our idea is that insular body size of mammals results from various selective forces whose influence varies not only with characteristics of the focal islands and the focal species, but also with interactions among species (ecological displacement and release). Our results, based on regression tree analyses, support this hypothesis of contextual body size evolution of insular mammals. While there may exist a theoretical optimal body size for mammals, in general, the optimum for a particular insular population varies in a predictable manner with characteristics of the islands and the species, and with interactions among species. This study did, however, produce some unanticipated results that merit further study – patterns associated with Bergmanns rule are amplified on islands, and body size of small mammals appears to peak at intermediate and not maximum values of latitude and island isolation. Lomolino MV, Sax DF, Palombo MR, van der Geer AAE. Of mice and mammoths: evaluations of causal explanations for body size evolution in insular mammals. Journal of Biogeography 39 (5): 842-854. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2699.2011.02656.x/abstract

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