Thursday, August 4, 2011

Environmental Concerns: Habitat Fragmentation

What is it?
Discontinuities in an organism's preferred environment causing population fragmentation (a form of population segregation). Habitat fragmentation includes 5 discrete phenomena:
  • Reduction in the total are of the habitat
  • Increase in the interior-edge ratio
  • Isolation of one habitat fragment from other areas of habitat
  • Breaking up of one patch of habitat into smaller patches
  • Decrease in the average size of each patch of habitat

What causes it?
Natural causes
  • Volcanism
  • Fire
  • Climate Change
Human Causes
Habitat fragmentation is frequently caused by humans when native vegetation is cleared for human activities such as agriculture, rural development, urbanization, and the creation of hydroelectric reservoirs. As a result of these activities, habitats that were once continuous become divided into separate fragments. These separate fragments tend to be isolated from each other separated by cropland, pasture, pavement or barren land. 

Habitat fragmentation reduces the amount of available habitat (such as rain forest, oceans, marshlands, etc.) for all organisms in an ecological niche. It also involves some degree of habitat destruction. Plants in these areas are usually directly destroyed while mobile animals like birds and mammals retreat into patches of habitat. This often results in crowding and increased competition which may be due in part to the fact that the remaining habitat fragments are smaller than the original habitat. Another issue with fragmentation is that species that cannot move between fragments must make due with what is available in the smaller, isolated patch of habitat; unfortunately, habitat fragments are rarely representative samples of the initial landscape making it difficult for less mobile species to survive. Thus, of significant importance is the area of the fragment.  The size of the new habitat influences the number of species which are present when the fragment was initially created and also influences the ability of these species to survive in the fragment. Small fragments can only support small populations of plants and animals; small populations, however, are more vulnerable to extinction. Therefore, habitat fragmentation is an important cause of species extinction.

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