29.11: Habitat Fragmentation
Habitat fragmentation describes the division of a more extensive, continuous habitat into smaller, discontinuous areas. Human activities such as land conversion, as well as slower geological processes leading to changes in the physical environment, are the two leading causes of habitat fragmentation. The fragmentation process typically follows the same steps: perforation, dissection, fragmentation, shrinkage, and attrition.
Perforation and dissection often occur during the initial stages of land development. For example, clearing undeveloped land to build a home (i.e., perforation) or road (i.e., dissection) disrupts the otherwise continuous habitat. Repeated habitat perforation or dissection, or a combination of both, creates an increasingly disconnected habitat - (i.e., fragmentation).
Shrinkage and attrition commonly ensue after fragmentation. Land development spreads until the remaining undeveloped areas become smaller (i.e., shrinkage) or completely disappear (i.e., attrition). Continued habitat destruction and fragmentation reduce habitat availability, which impacts biodiversity.
Fragmented land consists of edge and interior habitats. The edges of fragmented habitats are particularly vulnerable to environmental disturbances, such as severe weather. Larger habitat fragments withstand edge effects better than smaller fragments. Edge effects spread farther into and threaten the interior habitat when the edge-to-interior habitat ratio is high.
Small fragments support less biodiversity because: 1) edge effects create habitat instability, 2) some species require a large habitat, and 3) small, isolated populations are unsustainable long term. If a habitat is heavily fragmented, the risk of species extinction escalates as the native species lose access to suitable habitat. This risk is compounded if a species is unable to travel between patches, and gene flow is restricted.
Reconnecting fragmented habitats helps to mitigate the effects of habitat fragmentation. Aside from wildlife crossings, stepping-stones reconnect habitats by offering small patches of suitable habitat between larger habitat areas. Significant, protected habitats, such as nature reserves and national parks, present safe environments for species to thrive without further human activity. Habitat fragmentation studies aim to understand its effects on biodiversity and determine appropriate responses to reduce its detrimental effects.