Learning Objectives

16.2.1 Define and quantify species diversity and compare to biodiversity.

16.2.2 Define and graph rank abundance and species accumulation relationships.

16.2.3 Define species composition and explain why it is an important characteristic of communities.

We have seen that communities vary greatly in the number of species they contain. A tropical rainforest, for example, has many more tree species than a temperate rainforest, and a midwestern prairie has many more insect species than a New England salt marsh. Ecologists have devoted substantial effort to measuring this variation at a number of spatial scales. Species diversity and species composition are important descriptors of community structure, the set of characteristics that shape a community. Community structure is descriptive in nature but provides the necessary quantitative basis for generating hypotheses and experiments directed at understanding how communities work.