Question

Species-area curve is drawn by plotting the number of species against the area. How is it that when a very large area is considered the slope is steeper than that for smaller areas?

Answer 1

Specie area relationship:

• Specie area relationship was proposed and by Alexander von Humboldt.
• According to this, as the area explored increases species richness also increases but to a certain limit.

Where, $\text{Log S = Log C + Z Log A}$
S= Specie richness
A= Area
Z = Regression coefficient or slope of the line
C = Y intercept


Steeper slope :

• Within a region, species richness increases with increasing explored area, but only up to a limit; thus the value of Z (slope of the line) lies in the range of 0.1 to 0.2, irrespective of the taxonomic group or the region and slopes are similar for smaller areas.
• As a result when a very large area is considered the slope is steeper than that for smaller areas.
• When a very large area like the entire continent is considered, the species diversity increases significantly due to increase in availability of resources.
• This results in the value of Z within a range of 0.6 to 1.2 having much steeper slope.
• Example, the Z value for frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents is found to be 1.15.