Species Diversity and Abundance in Insular Systems

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This proposal seeks continuing support for research on food- web structure, species extinctions and ecological interactions. Small islands are used as a model system, because they are numerous, simple, discrete and have species and trophic types in various combinations. How top predators affect intermediate predators, ambient insects and foliage damage is studied in an introduction experiment of lizards onto small islets. The same phenomena, plus the degree to which intermediate predators compensate in top-predator absence, is studied in a lizard/spider removal experiment in large enclosures. A second experiment will measure spider competition with and without lizards. Natural extinction is studied using a system of over 100 islands; we focus on the effect of top predators on spider extinction rate, and on how extinction rate varies with mean, variability and skewness of population-size values over time and with life- history characteristics. Spatial patchiness in spider population distributions will be studied both between islands and within larger islands; the latter will be related to top predator occurrence and density. Characteristics of the founder effect (loss of genetic variability; degree of morphological and behavioral change) will be assessed for colonizing populations of lizards introduced onto islands during earlier support periods. The results will provide very valuable information on news relating to global the interactions leading to extinctions.