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A wildlife corridor, habitat corridor, or green corridor is an area of
habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
connecting
wildlife Wildlife refers to domestication, undomesticated animal species (biology), species, but has come to include all organisms that grow or live wilderness, wild in an area without being species, introduced by humans. Wildlife was also synonymous ...
populations separated by human activities or structures (such as roads, development, or logging). This allows an exchange of individuals between populations, which may help prevent the negative effects of
inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and o ...
and reduced genetic diversity (via
genetic drift Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear completely and there ...
) that often occur within isolated populations. Corridors may also help facilitate the re-establishment of populations that have been reduced or eliminated due to random events (such as fires or disease). This may potentially moderate some of the worst effects of
habitat fragmentation Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes ...
, wherein
urbanization Urbanization (or urbanisation) refers to the population shift from rural to urban areas, the corresponding decrease in the proportion of people living in rural areas, and the ways in which societies adapt to this change. It is predominantly t ...
can split up habitat areas, causing animals to lose both their natural habitat and the ability to move between regions to use all of the resources they need to survive. Habitat fragmentation due to
human development Human development may refer to: * Development of the human body * Developmental psychology * Human development (economics) * Human Development Index, an index used to rank countries by level of human development * Human evolution, the prehistoric ...
is an ever-increasing threat to
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
, and habitat corridors are a possible mitigation.


Purpose

The main goal of implementing habitat corridors is to increase
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
. When areas of land are broken up by human interference,
population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
numbers become unstable and many animal and plant species become endangered. By re-connecting the fragments, the population fluctuations can decrease dramatically. Corridors can contribute to three factors that stabilize a population: *
Colonization Colonization, or colonisation, constitutes large-scale population movements wherein migrants maintain strong links with their, or their ancestors', former country – by such links, gain advantage over other inhabitants of the territory. When ...
—animals are able to move and occupy new areas when food sources or other natural resources are lacking in their core habitat. *
Migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
—species that relocate seasonally can do so more safely and effectively when it does not interfere with human development barriers. *
Interbreeding In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in ...
—animals can find new mates in neighbouring regions, increasing genetic diversity. Rosenberg et al. (1995) were among the first to define what constitutes a wildlife corridor. The definitions of "
biological 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 roads, development, or logging). This allows an exchange of individuals between ...
" (i.e., wildlife corridor) had, in the early years of studying corridors, been "vague and inconsistent, and often they confound dform and function" Rosenberg et al. developed a
conceptual model A conceptual model is a representation of a system. It consists of concepts used to help people knowledge, know, understanding, understand, or simulation, simulate a subject the model represents. In contrast, physical models are physical object su ...
that emphasized the role of a wildlife corridor as a facilitator of movement that is not restricted by requirements of
native vegetation In biogeography, a native species is indigenous to a given region or ecosystem if its presence in that region is the result of only local natural evolution (though often popularised as "with no human intervention") during history. The term is equ ...
or intermediate target patches of habitat. Their definition simply required that movement to a target patch via the corridor be greater than if the corridor were absent. Although corridors had originally been implemented with the assumption that they would increase biodiversity, not enough research had been done to come to a solid conclusion. The case for corridors had been built more on intuition rather than
empirical evidence Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences and ...
(Tewksbury et al. 2002). Tewksbury et al. claimed that the early controversies had arisen because most studies had been limited in that they had a narrow taxonomic focus and, that if corridors facilitate animal movement, they should also have strong indirect effects on plant
populations Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
due to increased
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
and
seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
by animals. Results of their 2002 experiment provided a large-scale experimental demonstration that
habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
(or wildlife) corridors facilitate movement of disparate
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
between otherwise isolated patches even after controlling for area effects (Tewksbury et al., 2002). Another factor that needs to be taken into account is what species the corridor is intended for. Some species have reacted more positively to corridors than others. A habitat corridor could be considered as a possible solution in an area where the destruction of a natural area has greatly affected its
native species In biogeography, a native species is indigenous to a given region or ecosystem if its presence in that region is the result of only local natural evolution (though often popularised as "with no human intervention") during history. The term is equ ...
. Development such as
roads A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation. There are many types of ...
, buildings, and
farms A farm (also called an agricultural holding) is an area of land that is devoted primarily to agricultural processes with the primary objective of producing food and other crops; it is the basic facility in food production. The name is used fo ...
can interrupt plants and animals in the region being destroyed. Furthermore,
natural disaster A natural disaster is "the negative impact following an actual occurrence of natural hazard in the event that it significantly harms a community". A natural disaster can cause loss of life or damage property, and typically leaves some econ ...
s such as
wildfire A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire ...
s and
flood A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...
s can leave animals with no choice but to evacuate. If the habitat is not connected to a safer one, it will ultimately lead to death. A remaining portion of natural habitat is called a remnant, and to conserve species such portions need to be connected, because when migration decreases, extinction increases (Fleury 1997). Corridors can be made in two distinct areas—either water or land. Water corridors are called riparian ribbons and usually come in the form of rivers and streams. Land corridors come on a scale as large as wooded strips connecting larger woodland areas. However, they can also be as simple as a line of shrubs along a sidewalk (Fleury & Brown 1997). Such areas can facilitate the movement of small animals, especially birds, from tree to tree, until they find a safe habitat to rest in. Not only do minimal corridors aid in the movement of animals, they are also aesthetically pleasing, which can sometimes encourage the community to accept and support them.


Users

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, dispersal of a juvenile, or moving between parts of a large home range. Usually, large
herbivores A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
, medium to large
carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
s, and migratory species are passage users. One common misconception is that the corridor only needs to be wide enough for the passage users to get through. However, the corridor still must be wide enough to be safe and also encourage the animals to use it, even though they do not live out their entire lives in it. Corridor dwellers can occupy the passage anywhere from several days to several years. Species such as
plants Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...
,
reptiles Reptiles, as most commonly defined are the animals in the Class (biology), class Reptilia ( ), a paraphyletic grouping comprising all sauropsid, sauropsids except birds. Living reptiles comprise turtles, crocodilians, Squamata, squamates (lizar ...
, amphibians,
birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
,
insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of j ...
, and small
mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
can spend their entire lives in linear habitats. In this case, the corridor must include everything that a species needs to live and breed, such as soil for
germination Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...
, burrowing areas, and multiple other breeding adults.


Types

Habitat corridors can be categorized according to their width. Typically the wider the corridor, the more use it will get from species. However, the width-length ratio, as well as design and quality play just as important of a role in creating the perfect corridor (Fleury 1997). The strip of land will suffer less from
edge effect In ecology, edge effects are changes in population or community structures that occur at the boundary of two or more habitats. Areas with small habitat fragments exhibit especially pronounced edge effects that may extend throughout the range. As ...
s such as weeds, predators, and chemicals if it is constructed properly. The following are three divisions in corridor widths: * Regional – (> wide); connect major ecological gradients such as migratory pathways. * Sub-regional – (> wide); connect larger vegetated landscape features such as ridgelines and valley floors. * Local – (some <); connect remnant patches of gullies, wetlands, ridgelines, 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. When stepping stones are arranged in a line, they form a strip of land connecting two areas, just like a continuous corridor. Some kinds provide linkages between protected core areas and stimulate or allow species to migrate. Corridors can also be miniature in the form of
wildlife crossings Wildlife crossings are structures that allow animals to cross human-made barriers safely. Wildlife crossings may include underpass tunnels or wildlife tunnels, viaducts, and overpasses or green bridges (mainly for large or herd-type animals) ...
,
underpass A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube constr ...
es or overpasses used for crossing a man-made feature such as highways. They improve safety for both animals and humans. Many busy highways cross through natural habitats that native species occupy, as well. Large animals such as deer become a hazard when they cross in front of
traffic Traffic comprises pedestrians, vehicles, ridden or herded animals, trains, and other conveyances that use public ways (roads) for travel and transportation. Traffic laws govern and regulate traffic, while rules of the road include traffic ...
and are hit by vehicles. An overpass or an underpass serves as a bridge to facilitate the movement of animals across a busy road. 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 (Dole et al. 2003).


Costs

Corridors can be expensive to plan out and put into action. For example, Daniel Simberloff et al. state that “a bridge that would maintain a riparian corridor costs about 13 times as much per lane-mile as would a road that would sever the corridor.” He also states that maintenance of a corridor would be much more costly than refuges for
endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...
. It would simply be easier to move animals between refuges than to buy land, install a corridor, and maintain it. However, where the goal is not just to preserve a few large animal species but to protect biodiversity among all plants and animals, then habitat corridors may be the only option. Corridors are going to be expensive to implement no matter what, but it does depend on the type, location, and size, which can all vary to a great degree. With the lack of field data on the effectiveness; many organisations, government's, are not willing to consider putting their capital, efforts in green corridors.


Monitoring use

Researchers must pay attention to the population changes in animals after a corridor has been implemented to ensure that there are no harmful effects. Researchers can use both mark-recapture techniques and evaluate genetic flow to observe how much a corridor is being used. Marking and recapturing animals is more useful when keeping a close eye on individual movement. However, tagging animals and watching them does not give any data on whether the migrating individuals are successfully mating with other populations in connected areas of land. Genetic techniques can be more effective in evaluating migration and mating patterns. One of the most important goals of developing a corridor is to increase migration in certain animal species. By looking at a population's
gene flow In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...
, researchers can understand the genetic consequences of corridors via information about the migration patterns of an entire population instead of the movements of a few individuals. From these techniques, researchers can better understand whether or not habitat corridors are increasing biodiversity. Stephen Mech and James Hallett introduce an additional reason genetic techniques are more useful; they “measure average migration rates over time, which reveals the effects of fragmentation of several generations and is not as sensitive to current population sizes as mark-recapture studies are.” For example, when a population is extremely small, mark-recapture is almost impossible.


Design

According to new research, wildlife corridors are best built with a certain degree of randomness or
asymmetry Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in pre ...
, rather than built symmetrically. The research was conducted at the University of California, Davis. Wildlife corridors are susceptible to
edge effect In ecology, edge effects are changes in population or community structures that occur at the boundary of two or more habitats. Areas with small habitat fragments exhibit especially pronounced edge effects that may extend throughout the range. As ...
s; habitat quality along the edge of a habitat fragment is often much lower than in core habitat areas. Wildlife corridors are important for large species requiring significant sized
range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...
s; however, they are also vital as connection corridors for smaller animals and plants as well as ecological connectors to provide a ‟''
rescue effect The rescue effect is a phenomenon which was first described by Brown and Kodric-Brown,Brown JH, Kodric-Brown A. 1977 Turnover rates in insular biogeography: effect of immigration on extinction. Ecology 58, 445– 449. (doi:10.2307/ 1935620) and is ...
’’.''


Examples

Both the safety of animals and humans can be achieved through the creation of corridors. In
Alberta, Canada Alberta ( ) is one of the thirteen provinces and territories of Canada, provinces and territories of Canada. It is part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to t ...
, an overpass was constructed to keep animals off the busy highway which crosses a
national park A national park is a nature park, natural park in use for conservation (ethic), conservation purposes, created and protected by national governments. Often it is a reserve of natural, semi-natural, or developed land that a sovereign state dec ...
. The top of the bridge is covered in the native grass of the area. fences were also put on either side of the overpass to help guide animals in the right direction. In
Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural region that generally comprises the southern portion of the U.S. state of California. It includes the Los Angeles metropolitan area, the second most po ...
, 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 The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whit ...
, 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 how much use they got. From this experiment, much was learned about what would constitute a successful habitat corridor. In
South Carolina )''Animis opibusque parati'' ( for, , Latin, Prepared in mind and resources, links=no) , anthem = " Carolina";" South Carolina On My Mind" , Former = Province of South Carolina , seat = Columbia , LargestCity = Charleston , LargestMetro = ...
, 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. The most impressive dispersal into the connected region, though, was through bird droppings. Far more plant seeds were dispersed through bird droppings in the corridor-connected patch of land. There have also been positive effects on the rates of transfer and interbreeding in
vole Voles are small rodents that are relatives of lemmings and hamsters, but with a stouter body; a longer, hairy tail; a slightly rounder head; smaller eyes and ears; and differently formed molars (high-crowned with angular cusps instead of low-c ...
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. Researchers are not sure why the females did not move about as much, but it is apparent that the corridor effectively transferred at least some of the species to another location for breeding. In 2001, a wolf corridor was restored through a golf course in
Jasper National Park Jasper National Park is a national park in Alberta, Canada. It is the largest national park within Alberta's Rocky Mountains spanning . It was established as a national park in 1930 and declared a UNESCO World Heritage Site in 1984. Its locatio ...
,
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...
, which enabled
wolves The wolf (''Canis lupus''; plural, : wolves), also known as the gray wolf or grey wolf, is a large Canis, canine native to Eurasia and North America. More than thirty subspecies of Canis lupus, subspecies of ''Canis lupus'' have been reco ...
to pass through the course. After this restoration, wolves passed through the corridor frequently. This is one of the first demonstrations that corridors are used by wildlife, and can be effective in decreasing fragmentation. Earlier studies had been criticised for failing to demonstrate that corridor restoration leads to a change in wildlife behaviour.


Elephant corridor

Elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae an ...
corridors are narrow strips of land that allow elephants to move from one habitat patch to another. There are 88 identified elephant corridors in
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
. In Africa,
Botswana Botswana (, ), officially the Republic of Botswana ( tn, Lefatshe la Botswana, label=Setswana, ), is a landlocked country in Southern Africa. Botswana is topographically flat, with approximately 70 percent of its territory being the Kalahar ...
houses the largest number of free-roaming elephant herds. Elephants Without Borders (EWB) studies the movement of elephants is working to gain community support of local community corridors, so that elephants and humans can co-exist.


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 European Green Belt initiative is a grassroots movement for nature conservation and sustainable development along the corridor of the former Iron Curtain. The term refers to both an environmental initiative as well as the area it concer ...
* 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 Siju Wildlife Sanctuary is situated in the South Garo Hills district of Meghalaya, India. It is the first and oldest wildlife sanctuary in Meghalaya. It is also known as Siju Bird Sanctuary as it is a home for many rare and protected birds such as ...
and the Rewak Reserve Forest in
Meghalaya Meghalaya (, or , meaning "abode of clouds"; from Sanskrit , "cloud" + , "abode") is a states and union territories of India, state in northeastern India. Meghalaya was formed on 21 January 1972 by carving out two districts from the state of As ...
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 mammal, including tiger, clouded leopard and the Himalayan black bear. * The Ecologische Hoofdstructuur is a network of corridors and habitats created for wildlife in the
Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...
* The long Kanha-Pench elevated corridor on
NH 44 National Highway 44 (NH 44) is a major north–south National Highway in India and is the longest in the country. It passes through the Union Territory of Jammu and Kashmir, in addition to the states of Punjab, Haryana, Delhi, Uttar Pradesh, ...
. * Two elephant passes and two minor bridges on
NH 54 National Highway 306 (NH 306) is a National Highway in the Northeastern Indian states of Assam and Mizoram. NH 306 begins in Silchar, Assam at the intersection of NH 37 and generally runs southward passing through Lumding, Silchar and Kolas ...
in
Assam Assam (; ) is a state in northeastern India, south of the eastern Himalayas along the Brahmaputra and Barak River valleys. Assam covers an area of . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Manipur ...
’s Lumding Reserve Forest. * Three elephant underpasses, each with of vertical clearance on NH 72 and NH 58 in
Uttarakhand Uttarakhand ( , or ; , ), also known as Uttaranchal ( ; the official name until 2007), is a state in the northern part of India. It is often referred to as the "Devbhumi" (literally 'Land of the Gods') due to its religious significance and ...
, India. * Terai Arc Landscapes, Lower Himalayan Region.


Evaluation

Some animal species are much more apt to use habitat corridors than others depending on what their migration and mating patterns are like. For example, many cases of birds and butterflies successfully using corridors have been observed. Less successful stories have come out of mammals such as
deer Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reindeer ...
. How effective a corridor is may simply rely on what species it is directed towards. Corridors created with birds in mind may be more successful because they are highly migratory, to begin with. Human interference is almost inevitable with the quickly increasing population. The goal behind habitat corridors shows the most hope for solving habitat fragmentation and restoring biodiversity as much as possible. Although there are many positives and negatives, there may be enough positives to continue studying and improving corridors. It is truly difficult to say whether corridors are the solution to increasing biodiversity, because each one must be judged on its own. Each corridor has its own set of standards and goals that may set it apart from another one.


Negatives

A major downfall to habitat corridors is that not much information has been gathered about their success. Due to the lack of positive data, many agencies will not allow corridors to be established because they are unsure of their effectiveness. Another problem with corridors is that they are not as useful as simply preserving land so that it cannot be fragmented. However, it is becoming very difficult to set aside land for nature reserves when road-building, industry, and
urban sprawl Urban sprawl (also known as suburban sprawl or urban encroachment) is defined as "the spreading of urban developments (such as houses and shopping centers) on undeveloped land near a city." Urban sprawl has been described as the unrestricted growt ...
are all competing for space. Even if corridors are sought as a solution, it does not necessarily mean that animals will use them. Especially in the case of overpasses, research shows that animals do not like to use them to get to another remnant area of land. Usually overpasses are built over busy highways, and many species are too timid to expose themselves in front of all of the traffic. As more roads and buildings arise, there becomes less space to try to preserve. Habitat corridors need to be species-specific (not every kind of animal will use every kind of corridor) and corridors can be barriers to some species. For instance plants may use road verges as corridors however some mammals will not cross roads to reach a suitable habitat. When a corridor is implemented, many times development is so close by, that it becomes difficult to build a wide enough passage. There is usually a very limited amount of space available for corridors, so buffers are not usually added in. Without a buffer zone, corridors become susceptible to harmful outside factors from city streets,
suburb A suburb (more broadly suburban area) is an area within a metropolitan area, which may include commercial and mixed-use, that is primarily a residential area. A suburb can exist either as part of a larger city/urban area or as a separate ...
development, rural homes,
forestry Forestry is the science and craft of creating, managing, planting, using, conserving and repairing forests, woodlands, and associated resources for human and environmental benefits. Forestry is practiced in plantations and natural stands. Th ...
, cropland, and feedlots. Unfortunately, another limiting factor to the implementation of corridors is money. With such inconclusive data about the effectiveness of connecting land, it is difficult to get the proper funding. Those who would be in charge of the corridor design and construction would ask such questions as, “What if the corridors affect species negatively?” and “What if they actually aid in the spread of disease and catastrophic events?” Furthermore, there is a possibility that corridors could not only aid in the dispersal of native organisms, but invasive ones, as well. If
invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
take over an area they could potentially threaten another species, even to the point of extinction. Although wildlife corridors have been proposed as solutions to habitat and wildlife
population fragmentation Population fragmentation is a form of population segregation. It is often caused by habitat fragmentation. Causes of Fragmentation Fragmentation can be the cause of natural forces or human actions, although in modern times, human activity is th ...
, there is little evidence that they are broadly useful as a conservation strategy for all biodiversity in non-developed or less-developed areas, compared to protecting connectivity as the relevant ecological attribute. In other words, corridors may be a useful meme for conservation planning/ers, but the concept has less meaning to wildlife species themselves. Very few wildlife follow easily identified "corridors" or "linkages" (e.g., using
computer modeling Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be deter ...
), instead most species meander and opportunistically move through landscapes during daily, seasonal, and dispersal movement behavior. Wildlife corridors may be useful in highly developed landscapes where they are easily identified as the last remaining and available habitat.


Positives

Habitat corridors may be defenseless against a number of outside influences, but they are still an efficient way of increasing biodiversity. Strips of land aid in the movement of various animal species and
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
and
seed dispersal In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant. Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vectors, ...
, which is an added benefit to the intended one. For example, when insects carrying pollen or birds carrying seeds travel to another area, plant species effectively get transported, as well. Another positive aspect of corridors is that they allow both animals and humans to occupy virtually the same areas of land, and thus co-exist where without the corridor this would not be possible. Large animals such as
bear Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Nor ...
s can be attracted to residential areas in search of food due to lack of natural resources because of
habitat fragmentation Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes ...
. A corridor would provide a passage for the bears to
forage Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used m ...
in other locations, so that they would not pose as much of a threat to humans.


See also

* Aquatic organism passage *
Biolink zones Biolink zones are a land use category developed for biodiversity conservation and landscape adaptation under changing climates. Biolink zone was first coined in 1992 to encapsulate a potential new land-use resulting from research on vertebrate fauna ...
*
Emerald network The Emerald network is a network of Areas of Special Conservation Interest to conserve wild flora and fauna and their natural habitats of Europe, which was launched in 1989 by the Council of Europe as part of its work under the Convention on the ...
*
Habitat conservation Habitat conservation is a management practice that seeks to conserve, protect and restore habitats and prevent species extinction, fragmentation or reduction in range. It is a priority of many groups that cannot be easily characterized in term ...
*
Habitat destruction Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...
*
Landscape connectivity In landscape ecology, landscape connectivity is, broadly, "''the degree to which the landscape facilitates or impedes movement among resource patches''". Alternatively, connectivity may be a continuous property of the landscape and independent of p ...
*
Marine Protected Area Marine protected areas (MPA) are protected areas of seas, oceans, estuaries or in the US, the Great Lakes. These marine areas can come in many forms ranging from wildlife refuges to research facilities. MPAs restrict human activity for a conserv ...
*
Natura 2000 Natura 2000 is a network of nature protection areas in the territory of the European Union. It is made up of Special Areas of Conservation and Special Protection Areas designated under the Habitats Directive and the Birds Directive, respectively ...
*
The Pollinator Pathway The Pollinator Pathway is a participatory art, design and ecology social sculpture initiative founded by the artist and designer Sarah Bergmann. Its objective is to connect existing isolated green spaces and create a more hospitable urban environm ...
*
Roadkill Roadkill is an animal or animals that have been struck and killed by drivers of motor vehicles on highways. Wildlife-vehicle collisions (WVC) have increasingly been the topic of academic research to understand the causes, and how it can be mi ...
* Gary Tabor, wildlife corridor conservationist *
Tugay Tugay is a form of riparian forest or woodland associated with fluvial and floodplain areas in arid climates. These wetlands are subject to periodic inundation, and largely dependent on floods and groundwater rather than directly from rainfall ...
*
Wildlife crossing Wildlife crossings are structures that allow animals to cross human-made barriers safely. Wildlife crossings may include underpass tunnels or wildlife tunnels, viaducts, and overpasses or green bridges (mainly for large or herd-type animals); ...
*
Yellowstone to Yukon Conservation Initiative Yellowstone to Yukon Conservation Initiative or Y2Y is a transboundary Canada–United States not-for-profit organization that aims to connect and protect the 2,000 mile (3,200 kilometre) Yellowstone-to-Yukon region. Its mission proposes to mai ...


Further reading

* *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. *Department of Environment and Conservation (DEC). 2004. Wildlife Corridors. DEC, New South Wales. *Dole, J.W., Ng, S.J., Sauvajot, R.M. 2004. Use of Highway Undercrossings by Wildlife in Southern California. Biology Conservation, 115 (3):499-507. &Foreman, Dave. Rewilding North America: a Vision for Conservation in the 21st Century. Washington: Island, 2004. * *M., S. 2002. Ecology: Insects, Pollen, Seeds, Travel Wildlife Corridors. Science News, 162 (10):269. * *Roach, J. 2006. First Evidence that Wildlife Corridors Boost Biodiversity, Study Says. National Geographic Society, Washington, D.C. * * * *


References


External links


Defragmentation in Belgium (Flanders) - Connecting nature, connecting people. Accessed: 22 January 2009Wildlife passages - De-Fragmentation in the Netherlands - How to evaluate their effectiveness? Accessed: 22 January 2009CorridorDesign.org - GIS tools for designing wildlife corridors Accessed: 9 March 2010ConservationCorridor.org - information, tools and links to connect the science of landscape corridors to conservation in practice. Accessed: 14 September 2012
{{DEFAULTSORT:Wildlife Corridor Conservation biology Conservation projects Ecological connectivity Ecological restoration Environmental conservation Habitat Habitats Systems ecology Urban studies and planning terminology Wildlife conservation Animal migration