According to AV Humboldt, a German scientist, within a region, species richness increases with increase in explored area (upto certain limit). Accordingly, the relation between species richness and area for a wide variety of taxa (birds, bat, angiosperms, aquatic fishes) results in a rectangular hyperbola.
The relationship depicts a straight line on a logarithimic scale described by the following equation.
$$
\log \mathrm{S}=\log \mathrm{C}+\mathrm{Z} \log \mathrm{A}
$$
Where, ' $\mathrm{S}$ ' stands for species richness. ' $\mathrm{A}$ ' is area and ' $\mathrm{Z}$ ' and ' $\mathrm{C}$ ' are slope of line (regression coefficient) and y is intercept respectively.