On the Implications of Species-Area Relationships for Endemism, Spatial Turnover, and Food Web Patterns

Abstract

Consequences of species-area relationships (SARs) of the form S = cA are derived. One consequence is an endemics-area relationship (EAR); it is of the same power-law form as the SAR but with an exponent z' that is a function only of z and that always exceeds unity. An explicit formula is derived for the dependence of species turnover in space on census plot size, interplot distance, and the SAR exponent z; this formula can be used to determine z over spatial scales that are too large to permit direct estimate of z by censusing of nested patches. The areal dependence of link-species patterns observed in food webs is also examined; SARs are shown to imply the approximate, but not exact, area-independence of link-species relationships of the form L = kSy, where L is the number of trophic links and y < 2. A relationship between the average range of species in a habitat patch and the exponent z is also derived, leading to the result that average range is a decreasing function of both patch area and z.