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Biodiversity: Measuring Up To The Loss

Species are disappearing faster than biologists can identify and document them. Mindful of this crisis, nearly 200 countries (under the Convention on Biological Diversity) agreed to staunch the loss of biodiversity by 2010. However, to meet this goal, biologists need reliable metrics to monitor global trends in biodiversity. In the open access journal, PLoS Biology, Stuart Butchart from Birdlife International, Cambridge, UK, and others from Conservation International, IUCN and the Institute of Zoology, London, describe a new way to generate such an index that can measure trends in extinction risk for complete classes of organisms, starting with the world's 10,000 bird species. Their "Red List Index" measures changes in overall extinction risk over time for all bird species worldwide and shows "a steady and continuing deterioration in the status of the world's birds between 1988 and 2004," with "particularly steep declines" in recent years for Asian birds--resulting from massive deforestation in Indonesia--and for seabirds such as albatrosses and petrels, which drown on the hooks of commercial long-line fisheries.

Butchart et al. focus on evaluating trends in changes in threat status (extinction risk) by tracking the shift of individual species between the categories developed by the World Conservation Union (IUCN) Red List. Species are placed in categories on the Red List ranging from extinct to "least concern," according to criteria that take into account their population size, population trends, and range size. Thousands of scientists from around the world feed these assessments, which have been widely used to measure the degree of degradation of biodiversity.

Butchart et al. argue that Red List Indices complement indicators based on population trends, because although the indices show coarser temporal resolution, they have much better geographic representation; they're based on nearly all species in a group worldwide rather than on a potentially biased subset. The Red List Index therefore provides a reliable baseline to track progress toward the 2010 target, not only for birds but for all groups of organisms.

Source: Butchart SHM, Stattersfield AJ, Bennun LA, Shutes SM, Ak├žakaya HR, et al (2004) Measuring global trends in the status of biodiversity: Red List Indices for birds. PLoS Biol 2 (12): e383.

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