The species-area relationship or species-area curve describes the relationship between the area of a habitat and the number of species found within that area. Alexander Von Humboldt observed that within a region, species richness increased with increasing area, but up to a limit. The relation between species richness and area for a wide variety of taxa (plants, birds, fishes) turn out to be the rectangular hyperbola.
On a logarithmic (log) scale, the relationship is a straight line (linear) and is given by the following equation:
log S = log C + Z log A,
where, log S= species richness, Z= slope of the line, A= area, C= y-intercept.