A green forest corridor in Brazil
A wildlife Corridor in Brazil.

A wildlife corridor, habitat corridor, or green corridor[1] is an area of habitat connecting wildlife populations separated by human activities or structures (such as development, roads, or land clearing), allowing the movement of individuals between populations, that may help prevent negative effects of inbreeding and reduced genetic diversity (via genetic drift) that can occur within isolated populations. Corridors also help facilitate the re-establishment of populations that have been reduced or eliminated due to random events (such as fires or disease) and may moderate some of the worst effects of habitat fragmentation,[2] through urbanization that splits up habitat areas, causing animals to lose both their natural habitat and the ability to move between regions to access resources. Habitat fragmentation due to human development is an ever-increasing threat to biodiversity,[3] and habitat corridors serve to manage its effects.

Purpose

An urban green corridor in Lille.

Habitat corridors can be considered a management tool in places where the destruction of a natural area has greatly affected native species, whether it is a result of human development or natural disasters. When areas of land are broken up, populations can become unstable or fragmented. Corridors can reconnect fragmented populations and reduce population fluctuations by contributing to three factors that can help to stabilize a population:

Daniel Rosenberg et al.[4] were among the first to define what constitutes a wildlife corridor, developing a conceptual model that emphasized the role of a wildlife corridor as a facilitator of movement that is not restricted by requirements of native vegetation or intermediate target patches of habitat.[5]

Sign on a highway in Qatar, indicating an underpass that allows camels to safely cross.

Wildlife corridors also have strong indirect effects on plant populations by increasing pollen and seed dispersal from animals, facilitating movement of disparate taxa between isolated patches.[6] Corridors must be large enough to support minimum critical populations, reduce migration barriers, and maximize connectivity between populations.[7]

Wildlife corridors may also encompass aquatic habitats (often called riparian ribbons[8]) and usually come in the form of rivers and streams. Terrestrial corridors can come in the form of wooded strips connecting woodland areas or an urban hedge.[7]

Users

Most species can be categorized in one of two groups; passage users and corridor dwellers.

Passage users occupy corridors for brief periods of time. These animals use corridors for such events as seasonal migration, dispersal of juveniles, or moving between parts of a large home range. Animals such as large herbivores, medium to large carnivores, and migratory species are passage users.[9]

Corridor dwellers can occupy the passage anywhere from several days to several years. Species such as plants, reptiles, amphibians, birds, insects, and small mammals can spend their entire lives in linear habitats. In this case, the corridor must provide sufficient resources to support such species.[9]

Types

Habitat corridors can be categorized according to their width, with wider corridors generally encouraging more use.[10] However, overall corridor quality depends more on design when creating an effective corridor.[7] The following are three divisions in corridor widths:

Habitat corridors can also be divided according to their continuity. Continuous corridors are strips that are not broken up, while "stepping stone" corridors are small patches of suitable habitat. However, stepping-stone corridors may be more susceptible to edge effects.

Singapore highway
Singapore

Corridors can also take the form of wildlife crossings, underpasses or overpasses used for crossing human-made feature such as roads, reducing human-wildlife conflict such as roadkill. Observations have shown that underpasses are actually more successful than overpasses because many times animals are too timid to cross over a bridge in front of traffic and would prefer to be more hidden.[11]

Monitoring use

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Researchers can use mark-recapture techniques and hair snares in order to evaluate genetic flow to observe how a corridor is being used.[12] Marking and recapturing animals is more useful when keeping a close eye on individual movement.[13] However, tagging does not give any insight into whether the migrating individuals are successfully breeding with other populations.[citation needed]

Genetic techniques can be more effective when evaluating migration and mating patterns. By looking at a population's gene flow, researchers can understand the genetic consequences of corridors using information about the migration patterns of a population over time.[13]

Design

Wildlife corridors are most effective when they are designed with the ecology of their target species in mind. Other factors like seasonal movement, avoidance behavior, dispersal, and habitat requirements can be considered.[14]

Corridors are best built with a certain degree of randomness or asymmetry and when oriented perpendicular to habitat patches.[15][7] Wildlife corridors are susceptible to edge effects; habitat quality along the edge of a habitat fragment is often much lower than in core habitat areas. Habitat corridors are important for large species requiring significant-sized ranges; however, they are also vital as connection corridors for smaller animals and plants, as well as ecological connectors to provide a ‟rescue effect’’.[16] Wildlife corridors are additionally designed to reduce human-wildlife conflicts.[17]

Examples

In Alberta, Canada, overpasses have been constructed to keep animals off the Trans-Canada Highway, which passes through Banff National Park. The tops of the bridges are planted with trees and native grasses, and fences are present on either side to help guide animals.[18]

Florida highway
Florida

In Southern California, 15 underpasses and drainage culverts were observed to see how many animals used them as corridors. They proved to be especially effective on wide-ranging species such as carnivores, mule deer, small mammals, and reptiles, even though the corridors were not intended specifically for animals. Researchers also learned that factors such as surrounding habitat, underpass dimensions, and human activity also played a role in the frequency of usage.[19]

In South Carolina, five remnant areas of land were monitored; one was put in the center and four were surrounding it. Then, a corridor was put between one of the remnants and the center. Butterflies that were placed in the center habitat were two to four times more likely to move to the connected remnant rather than the disconnected ones. Furthermore, male holly plants were placed in the center region, and female holly plants in the connected region increased by 70 percent in seed production compared to those plants in the disconnected region. Plant seeds dispersal through bird droppings was noted to be the dispersal method with the largest increase within the corridor-connected patch of land.[20]

There have also been positive effects on the rates of transfer and interbreeding in vole populations. A control population in which voles were confined to their core habitat with no corridor was compared to a treatment population in their core habitat with passages that they could use to move to other regions. Females typically stayed and mated within their founder population, but the rate of transfer through corridors in the males was very high.[21]

In 2001, a wolf corridor was restored through a golf course in Jasper National Park, Alberta, which successfully altered wildlife behavior and showed frequent use by the wolf population.[22][23]

NH 44, Pench Tiger Reserve

Major wildlife corridors

Evaluation

Some species are more likely to utilize habitat corridors depending on migration and mating patterns, making it essential that corridor design is targeted towards a specific species.[36][37]

Due to space constraints, buffers are not usually added in.[4] Without a buffer zone, corridors can become affected by disturbances from human land use change. There is a possibility that corridors could aid in the spread of invasive species, threatening multiple populations.[38]

See also

Further reading

References

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