Wildlife corridor



A wildlife corridor, habitat corridor, or green corridor is an area of habitat connecting wildlife populations separated by human activities or structures (such as development, roads, or land clearings), 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, 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, and habitat corridors serve to manage its effects.

Purpose
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:
 * Colonization—animals are able to move and occupy new areas when food sources or other natural resources are lacking in their core habitat.
 * Migration—species that relocate seasonally can do so more safely and effectively when it does not interfere with human development barriers.
 * Interbreeding—animals can find new mates in neighboring regions, increasing genetic diversity.

Daniel Rosenberg et al. 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.



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

Wildlife corridors may also encompass aquatic habitats (often called riparian ribbons ) 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.

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.

Corridor dwellers can occupy the passage anywhere between 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.

Types
Habitat corridors can be categorized according to their width, with wider corridors generally encouraging more use. However, overall corridor quality depends more on design when creating an effective corridor. The following are three divisions in corridor widths:
 * Regional – (>500 m wide); connect major ecological gradients such as migratory pathways.
 * Sub-regional – (>300 m wide); connect larger vegetated landscape features such as ridge lines and valley floors.
 * Local – (some <50 m); connect remnant patches of gullies, wetlands, ridge lines, etc.

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.



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

Monitoring use
Researchers use mark-recapture techniques and hair snares to evaluate genetic flow and observe how a corridor is being used. Marking and recapturing animals can aid observing individual movement.

Genetic testing can help evaluate migration and mating patterns. By looking at a population's gene flow, researchers can better understand the role of corridors in migration patterns of a population over time.

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 are to be considered.

Corridors are best built with a certain degree of randomness or asymmetry and when oriented perpendicular to habitat patches. 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’’. '' Wildlife corridors are additionally designed to reduce human-wildlife conflicts.

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, with fences present on either side to help guide animals.

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.

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 seeds dispersal through bird droppings was noted to be the dispersal method with the largest increase within the corridor-connected patch of land.

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.

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.

Major wildlife corridors

 * The Paséo Pantera (also known as the Mesoamerican Biological Corridor or Paséo del Jaguar)
 * The Eastern Himalayan Corridor
 * China-Russia Tiger Corridor
 * Tandai Tiger Corridor
 * The European Green Belt
 * 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.
 * The Ecologische hoofdstructuur is a network of corridors and habitats created for wildlife in the Netherlands
 * The 16 km long Kanha-Pench elevated corridor on NH 44.
 * Two elephant passes and two minor bridges on NH 54 in Assam’s Lumding Reserve Forest.
 * Three elephant underpasses, each with 6 m of vertical clearance on NH 72 and NH 58 in Uttarakhand, India.
 * Terai Arc Landscapes, Lower Himalayan Region.

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.

Due to space constraints, buffers are not usually implemented. 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.