Week 6

Week 6 - REVIEWS REVIEWS REVIEWS Tropical turmoil a...

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79 © The Ecological Society of America www.frontiersinecology.org D espite some claims to the contrary, tropical biodiver- sity is in serious trouble. A recent flurry of scientific papers on the future of tropical biodiversity (reviewed in Laurance 2007) could give the impression that the state of tropical environments is not as dire as is widely believed. Tropical forests harbor more than 60% of all known species (Laurance 1999; Dirzo and Raven 2003), yet they represent only 7% of the Earth’s land surface. Documenting the state of this key biome is therefore an endeavor of paramount importance. As much as we would like to be bearers of good news, the sad reality is that tropical biodiversity has never been in worse shape. The debate mentioned above began with an analysis by Wright and Muller-Landau (2006) of current trends in tropical deforestation and human demographic projec- tions. They predicted that a tropical extinction crisis would be largely averted, because the rate of secondary re- growth would outstrip that of deforestation as rural human populations shifted into urban domains. Subsequent cri- tiques of those predictions (reviewed in Laurance 2007) challenged assumptions regarding (1) the inverse relation- ship between urban and rural human population trends, (2) the notion of decreasing demand for forest resources as urban populations expand, (3) human poverty projections (MA 2005), (4) the relatively lower biodiversity harbored by secondary forests compared to primary forests (eg Barlow et al . 2007; Laurance 2007; references therein), (5) the extinction debt in already depleted populations, and (6) the drivers of continued deforestation. Laurance (2007) concluded that the tropical extinction crisis was unlikely to be averted by human migration to urban areas. Yet, the debate highlights an important ques- tion: is there evidence that tropical ecosystems are suffi- ciently intact to safeguard existing biodiversity into the immediate future? We address this question by outlining the current state of knowledge of tropical biodiversity and evaluating whether there is sufficient cause for concern. Our conclusion is that we are already squarely in the midst of a tropical biodiversity tragedy and on a trajectory toward disaster. n Habitat loss – any improvement? It is predicted that habitat loss will affect terrestrial ecosystems more directly and profoundly than in even REVIEWS REVIEWS REVIEWS Tropical turmoil: a biodiversity tragedy in progress Corey JA Bradshaw 1,2,3* , Navjot S Sodhi 4 , and Barry W Brook 1 All is not well for biodiversity in the tropics. Despite recent debate over the extent of future tropical extinc- tions and the effectiveness of reserve systems, the continued disappearance of habitat, soaring human popula- tion, and loss of vital ecosystem services demand immediate action. This crisis is worrying, given that tropical regions support over two-thirds of all known species and are populated by some of the world’s poorest people, who have little recourse to lower environmental-impact lifestyles. Recent evidence has shown that – in addi-
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Week 6 - REVIEWS REVIEWS REVIEWS Tropical turmoil a...

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