Thursday, January 19, 2012

Climate Change and Extinctions

Biologists have long argued that the current rate of species loss rivals the five great mass extinctions of the geological past. As long ago as 1993, Harvard biologist E.O. Wilson estimated that Earth is currently losing something on the order of 30,000 species per year, or three species per hour. Some biologists have begun to feel that this biodiversity crisis — this “Sixth Extinction” — is even more severe, and more imminent, than Wilson had supposed. Significantly, where past extinction events were the result of physical processes, the current uptick is largely a product of human actions: transformation of the landscape and resultant habitat destruction, overexploitation of species, pollution, and the introduction of alien species. An article in the current issue of Nature argues that climate change may significantly increase the rate of species extinction through processes that have not previously been considered. Here's how Nature describes the article
More species may become extinct as a result of climate change than previously thought, a modelling study suggests. As the climate warms, many species are predicted to shift their ranges to stay within comfortable temperature zones. However, some species will be better able to do so than others. Mark Urban at the University of Connecticut in Storrs and his colleagues have created a model that takes into account the competition that species face for habitats when they move to new ecosystems. They modelled the effect of 4 °C of warming over 100 years on 40 simulated species, and found a much higher number of extinctions than did models that do not account for species competition and species' differing dispersal abilities. Even species with broad heat tolerances might be outcompeted — either by the arrival of newcomers in their current habitats or by native species in ecosystems that become habitable to them in future.
More technical details are provided in the abstract below:
Most climate change predictions omit species interactions and interspecific variation in dispersal. Here, we develop a model of multiple competing species along a warming climatic gradient that includes temperature-dependent competition, differences in niche breadth and interspecific differences in dispersal ability. Competition and dispersal differences decreased diversity and produced so-called ‘no-analogue’ communities, defined as a novel combination of species that does not currently co-occur. Climate change altered community richness the most when species had narrow niches, when mean community-wide dispersal rates were low and when species differed in dispersal abilities. With high interspecific dispersal variance, the best dispersers tracked climate change, out-competed slower dispersers and caused their extinction. Overall, competition slowed the advance of colonists into newly suitable habitats, creating lags in climate tracking. We predict that climate change will most threaten communities of species that have narrow niches (e.g. tropics), vary in dispersal (most communities) and compete strongly. Current forecasts probably underestimate climate change impacts on biodiversity by neglecting competition and dispersal differences.

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