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Biodiversity And Conservation

Hardbiology

According to the species-area relationship described by the equation log S equals log C plus Z log A, the slope value Z for very large areas such as entire continents generally lies in which range?

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About This Question

Subject
biology
Chapter
ecology and environment
Topic
biodiversity and conservation
Difficulty
Hard
Year
2025
Tags
species-area relationshipregression coefficient ZHumboldtspecies richnesslogarithmic scale

Solution

Correct Answer:

0.6 to 1.2

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.

This hard difficulty biology question is from the chapter ecology and environment, covering the topic of biodiversity and conservation. It appeared in the 2025 exam.

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