According to AV Humboldt, a German scientist within, a region, species richness increased with increasing explored area (only upto a limit). Accordingly the relation between species richness and area for a wide variety of taxa (birds, bat, angiosperms, aquatic fishes) turns out to be a rectangular hyperbola.

The relationship depicts a straight line on a logaithimic scale described by the following equation

$$ \log S=\log C+Z \log A $$

Where, ' $S$ ' stands for species richness, ' $A$ ' is area and ' $Z$ ' and ' $C$ ' are slope of line (regression coefficient) and y intercept respectively.