Question

A large forest area is fragmented into multiple smaller patches of different sizes. A researcher estimates the number of bird species in these forest fragments immediately following fragmentation, and then again 20 years later. The relationship between fragment size and species richness is shown in the graph for the two sampling events (immediately after fragmentation: closed circles and solid line; 20 years after fragmentation: open circles and dashed line). The best explanation for the differences in species richness with fragment size between the two sampling events is 

• A. Allen's rule.
• B. K-selection.
• C. Extinction debt.
• D. Bergmann's rule.

Hint:

Extinction debt occurs when species continue to survive in fragmented habitats for some time after the habitat's ability to support them has declined, leading to eventual local extinctions.

Answer 1

The Correct Option is C

In ecology, an extinction debt refers to the delayed loss of species in fragmented habitats. It occurs because species may persist in smaller habitat fragments for some time after fragmentation, even though the habitat is no longer able to support them long-term. Over time, species become locally extinct in these smaller, isolated habitats due to environmental changes, lack of resources, or other factors. This delayed extinction process can cause a difference in species richness immediately after fragmentation versus some years later, as seen in the provided graph.

Step 1: Analyzing the options.
- (A) Allen's rule: This rule states that animals in colder climates tend to have shorter appendages (ears, limbs) to conserve heat, which is not relevant to the question about species richness and habitat fragmentation. - (B) K-selection: This refers to a reproductive strategy where species produce fewer offspring with higher parental investment. While it relates to species survival strategies, it is not the best explanation for changes in species richness following habitat fragmentation. - (C) Extinction debt: This is the correct answer. It describes the phenomenon where species continue to exist in fragmented habitats even after the conditions for their survival have deteriorated, leading to eventual local extinctions. - (D) Bergmann's rule: This rule states that animals in colder regions tend to have larger body sizes, which is unrelated to species richness in fragmented habitats.

Step 2: Conclusion.
The correct answer is (C) because extinction debt explains the observed differences in species richness between the two sampling events.

Final Answer: (C) Extinction debt.