Question

Analysis of the species-area relationships indicate the value of Z to be in the range of:

• A. 0.1 to 0.5
• B. 0.5 - 1.1
• C. 0.6 - 1.2
• D. 1.2 - 2.0

Hint:

Understand the physical meaning of $Z$:
A smaller $Z$ value ($0.1$ to $0.2$) means species richness increases slowly with area (typical for small, uniform regions).
A larger $Z$ value ($0.6$ to $1.2$) indicates a much steeper slope, where species richness increases rapidly with area (typical for continental scales with diverse habitats).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question is from Ecology, specifically the chapter "Biodiversity and Conservation" in the NCERT Class 12 curriculum, focusing on species-area relationships formulated by the German naturalist and geographer Alexander von Humboldt.
We need to determine the range of values for the regression coefficient, represented by the constant $Z$.

Step 2: Key Concept or Approach:
Alexander von Humboldt observed that within a region, species richness increases with increasing explored area, but only up to a limit.
On a logarithmic scale, this relationship is expressed as a straight line with the equation:
\[ \log S = \log C + Z \log A \]
where $S$ is species richness, $A$ is the area, $C$ is the Y-intercept, and $Z$ is the slope of the line, also known as the regression coefficient.

Step 3: Detailed Explanation:

• Ecologists have discovered that for small or moderate-sized regions, the value of $Z$ lies in the range of $0.1$ to $0.2$, regardless of the taxonomic group or the geographic region.

• This means that whether we analyze plants in Britain, birds in California, or molluscs in New York state, the slopes of the regression lines are remarkably similar ($0.1$ to $0.2$).

• However, if we analyze the species-area relationship over very large areas like entire continents, the slope of the line is much steeper, with $Z$ values lying in the range of $0.6$ to $1.2$.

• For example, for frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents, the slope is found to be $1.15$.

• Since the general baseline value of $Z$ for standard ecological studies ($0.1$ to $0.2$) lies within the range of $0.1$ to $0.5$ in option (A), this is selected as the most appropriate standard option representing the baseline range.



Step 4: Final Answer:
The baseline value of $Z$ typically falls in the range of $0.1$ to $0.2$, which fits within the broader range of $0.1$ to $0.5$ in option (A).