Final answer:
Habitat fragmentation reduces alpha diversity primarily because it reduces the size of each habitat patch, leading to fewer species able to survive in the smaller, isolated areas. This decline in species diversity is associated with consequential genetic isolation and increased inbreeding within species. Larger patches correlate with richer biodiversity, and as these diminish, the species-area relationship predicts a loss in species richness. The correct option is 2) Habitat fragmentation reduces the size of each habitat patch.
Step-by-step explanation:
Habitat fragmentation caused by human activities can reduce alpha diversity in several ways, but option 2) Habitat fragmentation reduces the size of each habitat patch is most directly connected to the loss of alpha diversity. Habitat fragmentation leads to smaller and isolated patches which support fewer species, due to a lower diversity of available habitats, smaller population sizes, and a higher likelihood of local extinctions. This process can also lead to reduced genetic diversity within species, as fragmented populations become more isolated.
Furthermore, habitat fragmentation impacts species' ability to move between patches, thus reducing gene flow and increasing the chances of inbreeding depression. Larger patches typically harbor greater species diversity, as outlined by the species-area relationship, so when habitats are broken into smaller fragments, species richness generally declines.
Habitat fragmentation not only involves the subdivision of larger habitats but also intermixes these habitats with different land-uses, exposing species to environments that may not be conducive to their survival. Development such as roads and urban areas further contribute to the isolation of habitat patches and impede movement of species between these patches. This can have significant consequences for biodiversity.