Which of the following is true for species area relationship equation log S = log C + Z log A
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Large areas have higher 'Z' value
Option (1) Large areas have smaller 'Z' value — Incorrect. For very large areas, such as whole continents, the slope is steeper: Z values lie between 0.6 and 1.2. So large areas have higher, not smaller, Z values.
Option (2) Large areas have higher 'Z' value — Correct. In log S = log C + Z log A, Z is the slope of the line (regression coefficient), usually 0.1 to 0.2. For very large areas, such as whole continents, the slope is much steeper, with Z values of 0.6 to 1.2.
Option (3) 'C' in the equation is the regression coefficient — Incorrect. In this equation Z is the slope of the line, the regression coefficient. C is the Y-intercept.
Option (4) Species richness increases unlimitedly with increased explored area — Incorrect. Species richness increases with explored area, but only up to a limit, as Humboldt observed. It does not rise without limit.
NCERT Extract:
Patterns of Biodiversity – “… Ecologists have discovered that the value of Z lies in the range of 0.1 to 0.2, regardless of the taxonomic group or the region (whether it is the plants in Britain, birds in California or molluscs in New York state, the slopes of the regression line are amazingly similar). But, if you analyse the species-area relationships among very large areas like the entire continents, you will find that the slope of the line to be much steeper (Z values in the range of 0.6 to 1.2).”