Community composition and nested-subset analyses: Basic descriptors for community ecology

Three primary descriptors of community structure are the number, identities (composition), and abundances of species therein. Over the past 35 years, most attention has focused on relationships involving number (species-area and species-energy relation ships) or abundance distributions (broken-stick, geometric, log-normal, core-satellite, etc.). Composition patterns have bren underemphasized, even though several tools for addressing particular non-random patterns in species composition are available. One non-random pattern in community composition is nested subset structure. A community has a nested subset structure if the species found in depauperate replicates are also found in progressively more Species-rich assemblages. In this review, the problems of failing to consider composition patterns like nestedness are described, using species-area relationships and the SLOSS debate (single large or several small reserves) as an example. In addition, nestedness analyses are promoted as: 1) important descriptive tools for determining whether a community has this common non-random pattern of species composition, and 2) as important investigative tools for suggesting mechanisms potentially structuring a community.