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Wednesday, April 12, 2006

Species Extinction

A report published this week in the journal Conservation Biology details the possible species extinction consequences of continued global warming. The report - by Forestry specialist Jay Malcolm of the University of Toronto and an international team of conservation professionals - looked at the changes to vegetation types, or biomes, in 25 so-called 'hotspots' (unique ecosystems with a wide range of endemic species). In fact biodiversity hotspots are some of the richest and most threatened biological pools on Earth. They concentrate some 44 percent of plant and 35 percent of vertebrate species on only 1.4 percent of the Earth's land area. Each hotspot contains its own set of unique species. The researchers modeled what exactly might happen to the plants in these areas under the hypothesis that the atmospheric concentration of carbon dioxide doubles in the next 100 years.

Using a variety of models that project habitat changes and migration capabilities for a selection of species, they examined the possible related extinctions in 25 of these "hotspots," reaching the rather alarming conclusion that almost a quarter of the world's plant and vertebrate animal species could face extinction by 2050.

Here's the article abstract (and here's a pdf from the WWF which contains an earlier examination of the same issues):

Global Warming and Extinctions of Endemic Species from Biodiversity Hotspots

Abstract: Global warming is a key threat to biodiversity, but few researchers have assessed the magnitude of this threat at the global scale. We used major vegetation types (biomes) as proxies for natural habitats and, based on projected future biome distributions under doubled-CO2 climates, calculated changes in habitat areas and associated extinctions of endemic plant and vertebrate species in biodiversity hotspots. Because of numerous uncertainties in this approach, we undertook a sensitivity analysis of multiple factors that included (1) two global vegetation models, (2) different numbers of biome classes in our biome classification schemes, (3) different assumptions about whether species distributions were biome specific or not, and (4) different migration capabilities. Extinctions were calculated using both species-area and endemic-area relationships. In addition, average required migration rates were calculated for each hotspot assuming a doubled-CO2 climate in 100 years. Projected percent extinctions ranged from <1 to 43% of the endemic biota (average 11.6%), with biome specificity having the greatest influence on the estimates, followed by the global vegetation model and then by migration and biome classification assumptions. Bootstrap comparisons indicated that effects on hotpots as a group were not significantly different from effects on random same-biome collections of grid cells with respect to biome change or migration rates; in some scenarios, however, hotspots exhibited relatively high biome change and low migration rates. Especially vulnerable hotspots were the Cape Floristic Region, Caribbean, Indo-Burma, Mediterranean Basin, Southwest Australia, and Tropical Andes, where plant extinctions per hotspot sometimes exceeded 2000 species. Under the assumption that projected habitat changes were attained in 100 years, estimated global-warming-induced rates of species extinctions in tropical hotspots in some cases exceeded those due to deforestation, supporting suggestions that global warming is one of the most serious threats to the planet's biodiversity.

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