Human activities are causing widespread declines in biodiversity through both habitat destruction and the spread of invasive species. Predators are particularly vulnerable to population changes and even extinction. The resulting changes in predator species composition may, in turn, decrease or increase herbivore population densities, depending on whether predators act synergistically to reduce herbivores, or whether they compete with and/or eat each other. Hunting strategies of predators may be important in determining how they interact. In laboratory and field experiments different combinations of spider species, including the invasive spider Cheiracanthium mildei, will be manipulated to compare outcomes of interactions between predator species with similar and different hunting strategies. In addition, this research will assess whether the often spectacular success of invasive predators in species-poor managed ecosystems is due to the absence of ecologically similar native predator species. This study addresses two issues that are important in conservation: 1) biodiversity and 2) invasive species. By assessing the impact of predator diversity in the food web, it may be possible to identify species, or assemblages of species, that are important for preserving important ecosystem functions. This study will also examine the value of natural ecosystems in mitigating the spread of invasive species in nearby managed ecosystems. Results will have a direct impact on conservation efforts in the immediate area of study (Napa and Sonoma Counties, CA), but could have wide-reaching implications on how ecologists view the relationship between biodiversity and invasion.
