Local extinction refers to the complete disappearance of a species (or other taxon) from a specified geographic area, region, or habitat while that species continues to survive in some other part of the world. Local extinctions are contrasted with global extinctions in which the species no longer lives anywhere worldwide. Local extinctions often mark a change in the ecology of the affected area, such as a species disappearing due to introduction of a competing species from another location, such as with wolf reintroduction.
Causes of local extinction Local extinction occurs when environmental changes reduce a species' ability to survive in the particular habitat. Habitats may be changed, or even destroyed, by numerous natural processes or by human activity, with one or more local extinctions being a consequence. Some of these processes are described below. When habitats are destroyed or changed, by human activity or by natural processes, species populations may decline and then completely disappear from the affected region. Habitat fragmentation, in which a large continuous area is broken into a series of smaller isolated habitats can also contribute to local extinction by dividing continuous and connected habitats into smaller and more isolated patches. The isolation and reduction of habitat size can result in reducing total population size, slowing of movement between a set of smaller populations, and reduced genetic diversity for each sub-population which, in turn, increases risk of a major population collapse (Fahrig, 2003). Changes of natural ecosystems for agriculture, urban development, or other human activities are a significant cause of habitat destruction. Overexploitation of a species can also contribute to local extinction, due to members of a species being removed from a region faster than their ability to reproduce and recover. Overfishing, hunting, and poaching can reduce a population enough to make it more vulnerable to extinction in specific regions. Some species have been deliberately or systematically exterminated from both large and small geographical areas, for reasons including pest reduction, elimination of threats to agriculture and farming. Climate change increasingly impact species survival as changes in temperature, precipitation patterns, and severe weather impacts ecosystems. Smaller, declining, or isolated populations are more prone to extinction than large stable populations. A range of geological processes can also result in local extinctions, due to significant disturbances of natural habitats such as reforming land and sea features, exposure, introduction of toxic gases, and temporary or enduring temperature change. For example, glaciation during the Pleistocene glaciation event in North America resulted in death of most native North American species of earthworm due to glaciers covering a significant geographic area, leaving the region subsequently open for colonization by European earthworms transported in soil from Europe. Volcanic activity may also lead to significant numbers of local extinctions and possibly subsequent repopulation. The size of any geographic area affects the number of species, and the total population size, that it can sustain. This is particularly relevant for islands, where rise and fall of surrounding water changes a range of habitats, causing local extinctions or even, in cases of island endemism, outright extinction. Numerous examples of this occurred at the end of the Pleistocene period.
Metapopulation dynamics Metapopulation dynamics describe a model of how species survive across fragmented habitats and, conversely, how local extinction occurs. A metapopulation refers to a group of spatially separated populations of a single species that live in distinct habitats with some interconnected due to migration or dispersal. Species survival across different regions often depends on the specific balance and interaction between local extinction and recolonization events, in which populations may disappear from one habitat but be re-established due to individuals migrating from nearby populations (Hansik,1998). Habitat fragmentation can create connected networks causing some smaller populations to interact with each other, and the long term persistence of the species depends on the movement of the individuals species between habitats. Interruptions in dispersal between habitats increases the risk of permanent local extinction.(Harrison,1991).
Extinction debt Extinction debt refers to the existence of a species in an ecosystem despite a loss of habitat or other ecosystem features necessary for survival. A species may remain present in a habitat for a significant time after environmental degradation, after ecological changes have their chance of long term survival. (Tilman et al.,1994).
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