Wildlife corridor

A wildlife corridor, also known as a habitat corridor, or green corridor,^[1] is an designated area that connects wildlife populations that have been separated by human activities or structures, such as development, roads, or land clearings. These corridors enable movement of individuals between populations, which helps to prevent negative effects of inbreeding and reduced genetic diversity, often caused by genetic drift, that can occur in isolated populations. Additionaly, corridors support the re-establishment of populations that may have been reduced or wiped out due to random events like fires or disease. They can also mitigate some of the severe impacts of habitat fragmentation,^[2] a result of urbanization that divides habitat areas and restricts animal movement. Habitat fragmentation from human development poses an incresing threat to biodiversity, and habitat corridors help to reduce its harmful effects.

Habitat corridors can be considered a management tool in areas where the destruction of a natural habitats has severely impacted native species, whether due to human development or natural disasters. When land is fragmented, populations may become unstable or isolated. Corridors help reconnect these fragmented populations and reduce population fluctuations by supporting three key that stabilize population:

• Colonization: Animals can move and occupy new areas when food sources or other natural resources are scarce in their primary habitat.
• Migration: Species that relocate seasonally can do so more safely and effectively without interference from human development barriers.
• Interbreeding: Animals can find new mates in neighboring regions, increasing genetic diversity.

Daniel Rosenberg et al.^[3] were among the first to define the concept of wildlife corridor, developing a model that emphasized the corrido's role in facilitating of movement, unrestricted by the end for native vegetation or intermediate target patches of habitat.^[4]

Wildlife corridors also have significant indirect effects on plant populations by increasing pollen and seed dispersal through animals movement, of various species between isolated habitat patches.^[5] Corridors must be large enough to support minimum critical populations, reduce migration barriers, and maximize connectivity between populations.^[6]

Wildlife corridors may also include aquatic habitats often referred to as riparian ribbons,^[7]) and are typically found in the form of rivers and streams. Terrestrial corridors make take the form of wooded strips connecting forested areas or an urban hedgerows.^[6]

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

Passage users occupy corridors for brief periods. These animals use corridors for such events as seasonal migration, juveline dispersal or moving between different parts of a large home range. Large herbivores, medium to large carnivores, and migratory species are typical passage users.^[8]

Corridor dwellers, on the hand, can occupy a corridor for anywhere from several years. Species such as plants, reptiles, amphibians, birds, insects, and small mammals may spend their entire lives in linear habitats. In such cases, the corridor must provide enough resources to support such species.^[8]

Habitat corridors can be categorized based on their width, with wider corridors generally supporting greater wildlife use.^[9] However, the overall effectiveness of a corridor depends more on its design that its width.^[6] The following are three main categories of corridor widths:

• Regional – (>500 metres (1,600 ft) wide); connect major ecological gradients such as migratory pathways.
• Sub-regional – (>300 metres (980 ft) wide); connect larger vegetated landscape features such as ridge lines and valley floors.
• Local – (some <50 metres (160 ft)); connect remnant patches of gullies, wetlands, ridge lines, etc.

Habitat corridors can also be classified based on their continuity. Continuous corridors are uninterrupted strips of habitat,, while "stepping stone" corridors consist of small, separate patches of suitable habitat. However, stepping-stone corridors are more vulnerable to edge effects, which can reduce their effectiveness.

Corridors can also take the form of wildlife crossings, such an underpasses or overpasses that allow animals to cross man-made structures like roads, helping to reduce human-wildlife conflict, such as roadkill. Observations that underpasses tend to be more than overpasses as many animals are too timid to cross over a bridge in front of traffic and prefer the cover of an underpass.^[10]

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Researchers use mark-recapture techniques and hair snares to assess genetic flow and observe how wildlife utilizes corridors.^[11] Marking and recapturing animals helps track individual movement.^[12]

Genetic testing is also used to evaluate migration and mating patterns. By analyzing gene flow within a population, researchers can better understand the long- term role of corridors in migration and genetic diversity.^[12]

Wildlife corridors are most effective when designed with the ecology of their target species in mind. Factors such as seasonal movement, avoidance behavior, dispersal patterns , and specific habitat requirements must also be considered.^[13]

Corridors are more successful when they include some degree of randomness or asymmetry and are oriented perpendicular to habitat patches.^[14][6] However, they are vunerable to edge effects; habitat quality along the edge of a habitat fragment is often much lower than in core habitat areas.

While wildlife corridors are essential for large species that require exensive ranges; they are also crucial for smaller animals and plants,acting as ecological connectors to move between isolated habitat fragments. ^[15] Additionaly wildlife corridors are designed to reduce human-wildlife conflicts.^[16]

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, with fences present on either side to help guide animals.^[17]

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 played a role in the frequency of usage.^[18]

In South Carolina, five remnant areas of land were monitored; one was put in the center with the other four 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 seed dispersal through bird droppings was noted to be the dispersal method with the largest increase within the corridor-connected patch of land.^[19]

The 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 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.^[20]

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.^[21][22]

• The Paséo Pantera (also known as the Mesoamerican Biological Corridor or Paséo del Jaguar)^[23]
• The Eastern Himalayan Corridor^[24]
• China-Russia Tiger Corridor^[25]
• Tandai Tiger Corridor^[26]
• The European Green Belt^[27]
• The Siju-Rewak Corridor, located in the Garo Hills of India, protects an important population of elephants (thought to be approximately 20% of all the elephants that survive in the country). This corridor project links together the Siju Wildlife Sanctuary and the Rewak Reserve Forest in Meghalaya State, close to the India-Bangladesh border. This area lies within the meeting place of the Himalayan Mountain Range and the Indian Peninsula and contains at least 139 other species of mammals, including tigers, clouded leopards and the Himalayan black bear.^[28]
• The Ecologische hoofdstructuur is a network of corridors and habitats created for wildlife in the Netherlands^[29]
• The 16 kilometres (9.9 mi) long Kanha-Pench elevated corridor on NH 44.^[30]
• Two elephant passes and two minor bridges on NH 54 in Assam’s Lumding Reserve Forest.^[31][32]
• Three elephant underpasses, each with 6 metres (20 ft) of vertical clearance on NH 72 and NH 58 in Uttarakhand, India.^[33]
• Terai Arc Landscapes, Lower Himalayan Region.^[34]

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.^[35][36]

Due to space constraints, buffers are not usually implemented.^[3] 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 native populations.^[37]

• Beier, Paul; Noss, Reed F. (December 1998). "Do Habitat Corridors Provide Connectivity?". Conservation Biology. 12 (6): 1241–1252. Bibcode:1998ConBi..12.1241B. doi:10.1111/j.1523-1739.1998.98036.x. S2CID 16770640.
• Bennett, A.F. 1999. Linkages in the Landscape: The Role of Corridors and Connectivity in Wildlife Conservation. The World Conservation Union, Gland, Switzerland.
• De Chant, T. 2007. A Future of Conservation. Northfield Habitat Corridors Community Plan, Northfield, Minnesota.^[38]
• Department of Environment and Conservation (DEC). 2004. Wildlife Corridors. DEC, New South Wales.
• Dole, J.W., Ng, S.J., Sauvajot, R.M. 2003. Use of Highway Undercrossings by Wildlife in Southern California. Biology Conservation, 115 (3):499-507.^[18]
• Foreman, Dave. Rewilding North America: a Vision for Conservation in the 21st Century. Washington: Island, 2004.
• Fleury, A.M.; Brown, R.D. (1997). "A Framework for the Design of Wildlife Conservation Corridors with Specific Application to Southwestern Ontario". Landscape and Urban Planning. 37 (8): 163–186. Bibcode:1997LUrbP..37..163F. doi:10.1016/S0169-2046(97)80002-3. hdl:10214/4617.
• M., S. 2002. Ecology: Insects, Pollen, Seeds, Travel Wildlife Corridors. Science News, 162 (10):269.
• Mech, S.G.; Hallett, J.G. (2001). "Evaluating the Effectiveness of Corridors: a Genetic Approach". Conservation Biology. 15 (2): 467–474. Bibcode:2001ConBi..15..467M. doi:10.1046/j.1523-1739.2001.015002467.x. S2CID 84520743.
• Roach, J. 2006. First Evidence that Wildlife Corridors Boost Biodiversity, Study Says. National Geographic Society, Washington, D.C.^[39]
• Rosenberg, D.K.; Noon, B.R.; Meslow, E.C. (1997). "Biological Corridors: Form, Function, and Efficacy". BioScience. 47 (10): 667–687. doi:10.2307/1313208. JSTOR 1313208.
• Simberloff, D.; Farr, J.A.; Cox, J.; Mehlman, D.W. (1992). "Movement Corridors: Conservation Bargains or Poor Investments?". Conservation Biology. 6 (4): 492–504. Bibcode:1992ConBi...6..493S. doi:10.1046/j.1523-1739.1992.06040493.x.
• Sutcliffe, O.L.; Thomas, C.D. (1996). "Open Corridors Appear to Facilitate Dispersal by Ringlet Butterflies (Aphantopus hyperantus) between Woodland Clearings". Conservation Biology. 10 (5): 1359–1365. Bibcode:1996ConBi..10.1359S. doi:10.1046/j.1523-1739.1996.10051359.x.
• Tewksbury, J.J.; Levey, D.J.; Haddad, N.M.; Sargent, S.; Orrock, J.L.; Weldon, A.; Danielson, B.J.; Brinkerhoff, J.; Damschen, E.I.; Townsend, P. (2002). "Corridors Affect Plants, Animals, and Their Interactions in Fragmented Landscapes". PNAS. 99 (20): 12923–12926. Bibcode:2002PNAS...9912923T. doi:10.1073/pnas.202242699. PMC 130561. PMID 12239344.

• Defragmentation in Belgium (Flanders) - Connecting nature, connecting people. Accessed: 22 January 2009
• Wildlife Corridors Project Regeneration
• Wildlife passages - De-Fragmentation in the Netherlands - How to evaluate their effectiveness? Accessed: 22 January 2009
• CorridorDesign.org - GIS tools for designing wildlife corridors Accessed: 9 March 2010
• ConservationCorridor.org - information, tools and links to connect the science of landscape corridors to conservation in practice. Accessed: 14 September 2012