How does habitat fragmentation influence population structure and genetic diversity?

• A. Fragmentation reduces gene flow, increases isolation, elevates genetic drift, lowering genetic diversity and increasing differentiation.
• B. Fragmentation enhances gene flow and increases genetic diversity.
• C. Fragmentation has no effect on genetic diversity but increases carrying capacity.
• D. Fragmentation uniformly reduces all differentiation across populations.

Answer: (A)

Fragmentation disrupts movement of individuals and genes across the landscape, changing how populations exchange alleles. When habitat becomes divided into isolated patches, gene flow between patches drops because fewer individuals can move or reproduce in other patches. That makes each patch behave like a small, separate population, where genetic drift becomes stronger. Drift randomly removes alleles more quickly in small populations, reducing genetic diversity within patches. As the allele frequencies in different patches drift in different directions, populations become more genetically different from one another, increasing differentiation across the landscape.

This aligns with why the statement is correct: reduced gene flow, more isolation, stronger drift, lower diversity, and greater differentiation among fragments. The other ideas don’t fit because fragmentation does not boost gene flow, does not increase carrying capacity, and does not uniformly reduce differentiation.