When species richness is plotted vs area, the graph follows the equation : log S = log C + Z log A where Z is the slope of the line. Z values are usually in the range of 0.1 to 0.2 but if very large areas like entire continents are analyzed, the slope is much steeper. (0.6-1.2).
Why is it so ?
(Here S = species richness and A= area under consideration)