The value of 'Z' in the equation, log S = log C + Z log A, ranges from:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 0.1 to 0.2
In a region, the number of species rises as the area studied increases, but only up to a limit. This is the species-area relationship. On a log scale it becomes a straight line, log S = log C + Z log A. Here S is species richness, A is area, C is the Y-intercept, and Z is the slope of the line (the regression coefficient). Z tells how fast the number of species rises with area.
(1) 0 to 0.1 — Incorrect. This is below the range ecologists have found.
(2) 0.1 to 0.2 — Correct. For most regions Z lies between 0.1 and 0.2. This holds whatever the group or region: plants in Britain, birds in California or molluscs in New York state.
(3) 0.4 to 0.8 — Incorrect. This is not the usual range. Only for very large areas, such as whole continents, does the line become much steeper, with Z between 0.6 and 1.2.
(4) 0.01 to 0.02 — Incorrect. This is far too small.
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).”