Controls of the diversity and structure of grassland insect communities.

摘要

A central problem in ecology is understanding the processes that control the diversity of species in ecological communities. My dissertation research investigated the factors controlling arthropod diversity and community structure at Cedar Creek, Minnesota.; Physical disturbance may influence animal diversity. In a 30-year experiment, fire had little impact on savanna arthropod communities despite changes in physical factors and vegetation. This suggests interactions within the arthropod community are the primary structuring force.; Animal diversity may be controlled by predators or resources. Because the quantity, quality and heterogeneity of resources should affect the diversity of consumers, plant productivity and plant diversity may control the diversity of higher trophic levels. Alternatively, consumers may prevent competitive displacement in lower trophic levels, allowing a greater number of species to coexist.; I manipulated plant productivity versus diversity and composition independently and found increasing productivity increased arthropod abundance and diversity. Herbivore diversity depended on both plant diversity and composition. Predator and parasite diversity responded to herbivore diversity but also to vegetation characteristics suggesting plants control the animal diversity not only by changing the diversity of herbivores but also by influencing the interactions between herbivores and their enemies.; I explicitly manipulated plant species and functional diversity and found the diversity of arthropods increased with plant species diversity, with small increases after a few plant species. Parasite and predator species richness explained most of the variance in herbivore species richness, not plant characteristics. This suggests that herbivore diversity is primarily maintained by a diversity of parasites and predators that prevent competitive exclusion and allow a high diversity of herbivores to coexist on a single plant species.; Because many key ecological processes are dependent on body size, understanding the relationships among diversity, abundance and body size gives insight into the processes structuring communities. The most striking, and previously undiscovered, pattern I found was that the number of species within a size class (S) was related to the number of individuals (I) as {dollar}rm Ssim Iwedge 0.5{dollar}. This suggests that the rules determining the relative abundances of species within groups of arthropods of widely different body sizes and types are the same.