Explain how habitat fragmentation reduces biodiversity, referring to the effects on population size and gene flow.

Habitat fragmentation splits a continuous habitat into many smaller, isolated patches, so the total area available to each species is reduced.

Because the patches are smaller, the populations that can be supported in each one are also smaller. Small populations are more vulnerable to stochastic events and have fewer resources, which raises the risk of local extinction.

The isolation of the patches limits movement of individuals between them, so gene flow between populations is greatly reduced. With little gene flow, populations become genetically isolated and inbreeding increases. Inbreeding reduces genetic diversity, increases the expression of deleterious alleles and lowers the ability of the population to adapt to environmental change, further threatening its survival.