ABSTRACT 96-15151 Schoener Species Diversity and Abundance in Insular Systems This is a long-term experimental and observational study of food webs in islands of the Bahamas. A particular species in a food web may affect other species' abundances directly, via predation (predators reduce prey and, correspondingly, prey increase predators) or indirectly, via other species (e.g. predators may help plants indirectly by eating their herbivores). Previous experiments manipulated smaller predators to determine their direct and indirect effects. The proposed two experiments manipulate larger predators. First, large lizards will be introduced to places having smaller lizards. Second, birds and smaller lizards will be excluded in a crossed design. The two types of larger predators should differ fundamentally in their effects, particularly on plants: the former eat smaller predators, whereas birds also eat prey of the smaller predators, especially herbivorous insects. Additionally, immigrations (natural "introductions") and extinctions (natural "removals") on over 100 islands will be monitored to determine their frequency and long-term effects.
