Species-Area relationships

Scientists have long tried to establish a quantitative relationship between the diversity of species in a habitat and the size of that habitat, reasoning that larger areas can typically support more resources that can be shared among a greater number of species. The German naturalist Alexander von Humboldt was among the first to observe that species richness does increase with increasing area, but only up to a certain limit.

For most groups of species this relationship takes the form of a rectangular hyperbola: if S is species richness, A is the area under study, C is the Y-intercept and Z is the slope, the relationship can be written as S = CA^Z, or, taking logarithms of both sides, as log S = log C + Z log A. Plotted on ordinary axes the relationship rises and then flattens into a curve; plotted on a logarithmic scale it becomes a straight line (see Fig. 15.1). For comparatively small areas, the value of Z typically falls between about 0.1 and 0.2 regardless of the region or the group of species being studied. For much larger areas, such as entire co …