Global warming causes extinction of species
CLIMATE change brought about by the accumulation of carbon dioxide and other greenhouse gases in the atmosphere could lead to mass extinction of wildlife in isolated habitats (Conservation Biology, Vol 6 No 3). Global warming is expected to raise temperatures in the northern temperate latitudes by 2o to 6oC by the middle of the next century.
Biologists Kelly McDonald and James Brown at the University of New Mexico in Albuquerque have modelled the effect of global warming on animal populations living on isolated mountain ranges of the Great Basin in western north America. Fourteen species of mammals are presently found in the coniferous forests, meadows and streamside habitats in the higher reaches of the mountain ranges.
There is no migration of animals from one range to another as they are separated by hostile desert valleys, with hot dry climate and desert shrub vegetation. These montane islands represent the last vestige of woodland, forest, meadows and streams that were widely distributed over the area during the Pleistocene (Ice age) about one million years ago.
The scientists found that the species richness of this environment is determined by its area -- the number of species of woodland animals increases as the forest area grows. As the area of the forest above 2,280 m elevation -- the lower limit of the woodland -- increases, the number of species in these forests also increases.
Brown and McDonald say that with a 3oC rise in temperature, the habitable forest area will shrink. The lower border of the woodland would shift approximately 500 m upwards. As the area of suitable habitat shrinks, the distribution and abundance of each mammal species will decrease proportionately till extinction occurs. They found a warming of 3oC can cause a loss of 9 per cent to 62 per cent of the small mammal species in each mountain range and the extinction of three of 14 species throughout the region.
The habitat of the Toquima-Monitor range, for example, will go down from 455 sq km to 230 sq km and the number of species would reduce from 11 to nine. The two species on the Toquima-Monitor range that are most likely to go extinct are Ochotona princeps and Zapus princeps. The scientists predict that three species -- Zapus princeps, Spermophilus beldingi and Lepus townsendii -- are likely to go extinct from the entire area and only two species -- Eutamias umbrinus and Neotoma cinerea -- are likely to survive on the mountains they occur.
As a result of the studies, the scientists caution the species inhabiting the "habitat islands" are especially vulnerable to climate change and that any conservation strategy based solely on isolated reserves is very susceptible to global or regional change.
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