29.11:
Habitat Fragmentation
Habitats provide vital resources—such as food, shelter, and mates—that support an organism’s survival. A dense, continuous forest habitat, for example, hosts a sizable and diverse wildlife population. However, natural forces and human activity can change a habitat and impact the resident organisms.
Habitat fragmentation is the process by which a formerly continuous habitat is divided into smaller, isolated areas.
A road cutting through a forest, for example, creates habitat discontinuity that may impede access to key resources for animals.
Additional human activities, like the clearcutting of trees, can further fragment the habitat. Organisms that cannot relocate to another suitable habitat go extinct. Meanwhile, surviving organisms are at increased risk of extinction because the smaller, fragmented populations have less genetic diversity.
Natural forces also cause habitat fragmentation.
River fluctuations, for example, impact both terrestrial and aquatic wildlife. River flooding may block the passage of terrestrial animals. If the river dries up, migratory aquatic animals may lose their passageway between water bodies.
Habitat fragmentation results in population isolation, habitat loss, and biodiversity reduction.
Edge effects are another common consequence of habitat fragmentation. Edge effects are changes that occur at transitional regions between habitats. For instance, a forest edge abutting an agricultural field is more prone to fires. The increased light exposure dries out the forest vegetation, increasing the chances of a fire.
Since human activity is the primary cause of habitat fragmentation, it is important to mitigate its effects. Wildlife crossings, for example, create corridors for wildlife to safely cross human-made habitat barriers, like roads. Reconnecting fragmented habitats is one of many conservation approaches in use today.
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.
Suggested Reading
Crooks, Kevin R., Christopher L. Burdett, David M. Theobald, Sarah R. B. King, Moreno Di Marco, Carlo Rondinini, and Luigi Boitani. 2017. “Quantification of Habitat Fragmentation Reveals Extinction Risk in Terrestrial Mammals.” Proceedings of the National Academy of Sciences 114 (29): 7635–40. [Source]
Wilson, Maxwell C., Xiao-Yong Chen, Richard T. Corlett, Raphael K. Didham, Ping Ding, Robert D. Holt, Marcel Holyoak, et al. 2016. “Habitat Fragmentation and Biodiversity Conservation: Key Findings and Future Challenges.” Landscape Ecology 31 (2): 219–27. [Source]