Question

The great German naturalist and geographer Alexander Von Humboldt observed that within a region species richness increased with increasing explored area, but only upto a limit.

1. For the above situation, construct a graph and write an equation.
2. Also write various values of Z (regression coefficient).

Answer 1

a. Graph and equation:

Alexander Von Humboldt noted that there is a logarithmic relationship between species richness (S) and the investigated area (A). The species-area curve on the graph indicates that species richness rises but decreases with the investigated area.

The equation for this relationship is:

S = CA^Z

Where:

S = Species richness

C = A constant (specific to the ecosystem)

A =  Area explored

Z = Regression coefficient (slope of the log-log graph)

Graph representation:

The curve shows a saturation point where increasing area produces a minor increase in species richness. It begins steeply but levels off as the area grows.

b. Various Values of Z (Regression Coefficient)

The value of Z varies depending on the type of ecosystem:

Ecosystem type	Value of Z
Small areas within a single region (e.g., a forest)	0.1-0.2
Large areas across a continent	0.6-1.2
Entire continents (Fruit eating birds and mammals in the tropical forests)	∼1.15 (approaching 1)

• Z between 0.1 and 0.2 indicates a slow rise in species richness with area.
• For a wide area, species richness rises quickly when Z is between 0.6 and 1.2.
• High species turnover across several regions is indicated when Z gets close to 1.