(a) Explain the species area relationship using the graphical representation given below.
(b) Explain giving reasons why there is greater biodiversity in tropical regions of the Earth.
(a) (i) Alexander Von Humboldt has observed that within a region, species richness
increased with increased explored area, but only upto a limit.
(ii) The relationship between species richness and for a number of taxa like angiospermic plants,
freshwater fishes and birds is found to be a rectangular hyperbola.
(iii) On a logarithmic scale, the relationship is a straight line described by the equation.
log S=log C+Z log A
(iv) Ecologists have discovered that the value of Z lies in the range between 0.1 and 0.2
regardless of the taxonomic group of the region wether it is the plants in Britain, birds in
California or molluses in New York State, the slopes of the regression line are amazingly
(v) If species area relationship is very large like the entire continents then the slope of the line
is much sleeper (Z values in the range of 0.6-1.2).
E.g. for frugivores (fruit eating) birds and mammals in the tropical forests of different continents,
the slope is found to be 1.15.
(b) Tropical environments are less seasonal, relatively more constant and predictable. Such
constant environments promote niche specialisation and lead to a greater species diversity.
There is more solar energy in tropics, which contributes to more productivity. This results
indirectly to greater diversity. Tropical latitudes have remained relatively undisturbed
for millions of years and so had a long evolutionary time for species diversification.