In species-area relationships equation - log S = log C + Z log A'Z' d…

The correct answer is Option (3) → Regression coefficient

The species-area relationship tells how the number of species rises as the area studied grows. Drawn on a log scale it is a straight line, and Z is its slope: it tells how fast species richness rises with area. For small areas Z usually lies between 0.1 and 0.2, whatever the group of organisms or the region. For very large areas such as whole continents the line is much steeper, with Z between 0.6 and 1.2.

Option (3) Regression coefficient — Correct. The slope of a straight line fitted to data is called the regression coefficient, and that is Z.

Note: The same question was also asked in CUET (UG) 2025 on 29-05-2025 (Slot 1) and on 14-05-2025 (Slot 2), and a similar question in CUET (UG) 2026 on 30-05-2026 (Slot 2).

NCERT Extract:
Patterns of Biodiversity – “… (ii) Species-Area relationships : During his pioneering and extensive explorations in the wilderness of South American jungles, the great German naturalist and geographer Alexander von Humboldt observed that within a region species richness increased with increasing explored area, but only up to a limit. In fact, the relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola (Figure13.2). On a logarithmic scale, the relationship is a straight line described by the equation
log S = log C + Z log A
where
S= Species richness   A= Area
Z = slope of the line (regression coefficient)
C = Y-intercept
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).”

Figure 13.2 Showing species area relationship. Note that on log scale the relationship becomes linear