Species diversity trends — theories and hypotheses

Abstract

We are now in a better position to try and explain the species diversity trends described in Chapter 1. If communities can become saturated, then species diversity differences may be simply related to the age of the community and the degree of saturation, i.e. the extent to which all available resources are exploited by as many species as possible. However, saturated communities can also differ in species diversity. MacArthur [28] derived a simple equation to approximate species diversity of animals (Ds) using a common resource

$$ Ds = {{Dr} \over {Du}}\left( {1 + C\bar \alpha } \right)$$

describes the diversity of resources used by the entire community, Du describes the niche width of each species (assumed identical), C is the number of potential competitors or neighbours in niche space — an expression of the dimensionality of the habitat, ᾱ is the mean competitive coefficient or mean niche overlap. Although little used, this formulation provides a useful basis for the following discussion, and predicts that saturated communities can differ in species diversity in three, potentially interacting ways.