Question

The graph shows bird species richness in a large contiguous forest patch and a small adjacent forest fragment, before and soon after the large contiguous forest patch was replaced by an oil palm plantation.
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Which one of the following options best explains the pattern shown?

• A. The contiguous forest is a sink and the forest fragment is a source for bird species.
• B. The forest fragment has higher species richness than the contiguous forest.
• C. The bird community in the forest fragment is geographically closed.
• D. The contiguous forest was contributing to forest fragment species richness via dispersal.

Hint:

To interpret habitat connectivity: 1. Source habitats contribute species to adjacent fragments through dispersal.
2. Fragmented landscapes often depend on connectivity to maintain biodiversity.
3. Habitat loss can disrupt dispersal, leading to declines in species richness.

Answer 1

The Correct Option is D

Step 1: Interpret the graph. The graph shows:
Before the replacement, the contiguous forest had higher species richness than the forest fragment.
After the replacement of the contiguous forest with an oil palm plantation, the species richness in the forest fragment drastically decreased.
Step 2: Analyze the ecological dynamics. The decrease in species richness in the forest fragment after the loss of the contiguous forest suggests that:
1. The contiguous forest acted as a source habitat, providing species that dispersed into the forest fragment.
2. The removal of the contiguous forest disrupted dispersal, leading to a loss of species in the forest fragment.
Step 3: Evaluate the options. Option (A): Incorrect. A sink is a habitat where populations decline without immigration. The contiguous forest was likely a source, not a sink. Option (B): Incorrect. The forest fragment initially had lower species richness than the contiguous forest, as shown in the graph. Option (C): Incorrect. A geographically closed community would not depend on dispersal from the contiguous forest, contradicting the observed pattern. Option (D): Correct. The contiguous forest contributed to the species richness of the forest fragment via dispersal. Its removal caused a decline in species richness in the fragment.