9 - Community Structure

Abstract

This chapter focuses on the approaches for describing a community structure, and on the biogeographic patterns and underlying factors contributing to a community structure. Communities are composed of the species occupying a site. Identification of patterns in community structure has been a major goal of ecological research. However, no standard approach for delimiting a site and describing or comparing community structure has been adopted. Indices of species diversity, food web structure, and functional group organization are three methods used to facilitate comparison among communities. Species diversity has two components: richness and evenness. Richness is the number of species in the community, whereas evenness is a measure of the relative abundances. Geometric rank-abundance curves characterize harsh or disturbed habitats with a limited number of adapted species and strong dominance hierarchy, whereas log and broken stick models characterize more stable habitats with higher species accumulation and greater evenness in abundance among species. Food web structure represents the network of pairwise interactions among the species in the community. A number of food web attributes have been proposed based on limited taxonomic resolution of insects and other arthropods. Functional group organization reflects a combination of species on the basis of functional responses to environmental variables or effects on ecological processes, regardless of taxonomic affiliation. Habitat area and stability, resource availability, and species interactions are the major factors that affect a community structure. Habitat area affects the pool of species available and the heterogeneity of habitat conditions and resources.