Biodiversity And Conservation

Alexander von Humboldt observed that within a region species richness increases with explored area but only up to a limit, and the relationship is a rectangular hyperbola. On a logarithmic scale it becomes the straight-line equation log S = log C + Z log A, where S is species richness, A is area, C is the Y-intercept, and Z is the slope known as the regression coefficient. For relatively small areas within a continent, the value of Z typically lies between 0.1 and 0.2 regardless of the taxonomic group studied. However, when the species-area relationship is analysed for very large areas such as entire continents, the slope Z becomes much steeper, lying in the range of 0.6 to 1.2. The option 0.1 to 0.2 is the range for small areas, not continents, so it is incorrect here. The ranges 1.5 to 2.0 and 0.001 to 0.01 are not values reported in the NCERT text for the slope. As described in NCERT Class 12, Chapter 15 (Biodiversity and Conservation), the steeper slope for continents reflects the inclusion of diverse, distinct biotas. Plausibility check: larger and more heterogeneous areas accumulate species faster, so a steeper slope for continents is internally consistent.