Species–Area relationships: German naturalist and geographer Alexander von Humboldt while exploring the South American jungles, found that within a region species richness increased with increasing explored area but only up to a limit. The relationship between species richness and area turned out to be a rectangular hyperbola for a wide variety of organisms like angiosperm plants, birds bats and freshwater fishes. The relationship is a straight line on a logarithmic scale. It is mathematically expressed as:

S = CA^Z

OR

log S = log C + Z log A

where,
S = Species richness
A = Area
Z = Slope of the line (regression coefficient)
C = Y–intercept