The
Global Amphibian Decline:
Trends, Causes, and Challenges
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The
Global Amphibian Decline: |
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Jordan's salmander |
| Introduction
Global
Trends Causes
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Actual Cause: Habitat Modification Habitat modification is the best documented human-induced cause of amphibian population declines. The current rates of tropical deforestation and the suspected losses in biodiversity associated with it are well documented. However, habitat is a cause of amphibian declines in temperate systems as well. In Britain, populations of the crested newt (Triturus cristatus) and natterjack toad (Bufo calamita) in Britain have gradually decreased over the last 30 years as breeding sites are consumed by agricultural or building development. Habitat loss reduces amphibian abundance and diversity in the areas directly affected. For instance, removal or modification of vegetation in forestry operations has a rapid and severe impact on some amphibian populations because logging exposes terrestrial amphibians to altered microclimate regimes, soil compaction and dessication, and reduction in habitat complexity. Clearcutting of mature forests in the southern Appalachian Mountains reduced salamander populations by more than a quarter billion individuals (9%), affecting all species and major taxonomic groups. Clearcutting has also been found to completely eliminate a local populations of Jordan's salamander (Plethodon jordani, above) in the southern Appalachians. In stream environments, deforestation exposes aquatic amphibians to increased siltation and reduced woody debris. Although populations may recover as forests regenerate and mature, recovery to predisturbance levels can take several decades. Draining wetlands also directly affects frog populations by removing
breeding sites and by fragmenting populations, increasing the probability
for local extinctions. Populations of some amphibians in Florida declined
after degradation of upland, dry season refuges and human modification
of wetlands used for breeding. However, protection of aquatic breeding
sites may be of little value if adjacent terrestrial habitats used by
amphibians for feeding and shelter are destroyed. Local habitat destruction can also have negative effects on adjacent amphibian populations. Migration to sites vacated due to extinctions of local subpopulations is already difficult for amphibians because of their tendency to move only relatively short distances, their extreme site fidelity, and their very specific moisture and temperature needs. When severe habitat fragmentation occurs, subpopulations can decline and become extinct when unsuitable habitat between separate groups prevents recolonization |
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