Question

What are the inferences you can draw from this graph?

• A. Slope of line ‘a’ is smaller than slope of line ‘b’
• B. Z value for line ‘a’ is greater than Z value for line ‘b’
• C. If line ‘b’ is a plot of the mainland (much larger area), line ‘a’ is likely to be the plot of an island (smaller isolated area)
• D. log C value is the same for both the lines

Answer 1

Answer: (A), (C)

The correct options are
A Slope of line ‘a’ is smaller than slope of line ‘b’
C If line ‘b’ is a plot of the mainland (much larger area), line ‘a’ is likely to be the plot of an island (smaller isolated area)

The equation: log S = log C + Z log A represents the relationship between species richness and area. This is a linear equation in the form ‘y = c+mx’. Comparing these two equations, y = log S; x = log A; the constant c = log C and Z is the slope m. Steeper lines have larger slopes and flatter lines have smaller slopes. Therefore slope of line ‘a’ is smaller than slope of line ‘b’ or in other words the Z value of line a is smaller than the Z value of line b. Ecologists have seen that Z value for most geographical areas and taxa tend to be the same, but larger areas tend to have relatively higher Z value than small isolated areas. Therefore line b is likely to be the plot of the mainland and line a - the plot of an island. log C is the y-intercept of two lines, and as you can see if the two lines are extrapolated to intercept the y axis, they would intercept at different points and therefore, log C for both the lines are different.