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Download Ecological effects of habitat fragmentation and edge creation
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Ecological effects of habitat fragmentation and edge creation Dr. Peter Minchin Department of Biological Sciences Habitat fragmentation involves both a reduction in the total area of habitat and a change of configuration into smaller and more isolated patches, embedded in a highly altered matrix. The phenomenon is complex and largely system-specific, but some generalizations about the biological consequences of fragmentation are starting to emerge from research in conservation biology. There is generally an inverse relationship between the number of extinctions in fragments and their area: larger fragments have a lower rate of extinction than smaller ones. A group of smaller fragments loses more species than a single fragment of equivalent total area. Equally important as the reduction is area is that the fragments become isolated. Movement of species among patches is inhibited by the intervening matrix or the existence of barriers such as roads. Isolation of populations in small patches has negative genetic effects, including inbreeding depression and the loss of variation. The boundary of a habitat fragment is not sharp. Rather, there is an edge zone of varying width for different factors. In forests, the altered environment of the edge zone favors shade intolerant plant species at the expense of the forest dominants and can also favor the proliferation of invasive species. Since the perimeter of a polygon decreases more slowly than its area, smaller patches have a larger ratio of edge to interior. Patches below a certain area may be essentially all edge, with no core habitat remaining. The deleterious effects of edges on biodiversity contradict the idea promoted by some wildlife managers that “edge is good”. Most terrestrial game species in the USA (e.g. white-tailed deer) are edge-adapted animals whose populations respond positively to the amount of edge.