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Loss of biodiversity appears to affect ecosystems as much asclimate change, pollution and other major forms of environmentalstress, according to results of a new study by an internationalresearch team. The study is the first comprehensive effort todirectly compare the effects of biological diversity loss to theanticipated effects of a host of other human-caused environmentalchanges. The results, published in this week's issue of the journal Nature,highlight the need for stronger local, national and internationalefforts to protect biodiversity and the benefits it provides,according to the researchers, who are based at nine institutions inthe United States, Canada and Sweden. "This analysis establishes that reduced biodiversity affectsecosystems at levels comparable to those of global warming and airpollution," said Henry Gholz, program director in the NationalScience Foundation's Division of Environmental Biology, whichfunded the research directly and through the National Center forEcological Analysis and Synthesis. "Some people have assumed that biodiversity effects are relativelyminor compared to other environmental stressors," said biologistDavid Hooper of Western Washington University, the lead author ofthe paper. "Our results show that future loss of species has the potential toreduce plant production just as much as global warming andpollution." Studies over the last two decades demonstrated that morebiologically diverse ecosystems are more productive. As a result, there has been growing concern that the very highrates of modern extinctions--due to habitat loss, overharvestingand other human-caused environmental changes--could reduce nature'sability to provide goods and services such as food, clean water anda stable climate. Until now, it's been unclear how biodiversity losses stack upagainst other human-caused environmental changes that affectecosystem health and productivity. "Loss of biological diversity due to species extinctions is goingto have major effects on our planet, and we need to prepareourselves to deal with them," said ecologist Bradley Cardinale ofthe University of Michigan, one of the paper's co-authors. "Theseextinctions may well rank as one of the top five drivers of globalchange." In the study, Hooper, Cardinale and colleagues combined data from alarge number of published studies to compare how various globalenvironmental stressors affect two processes important inecosystems: plant growth and the decomposition of dead plants bybacteria and fungi. The study involved the construction of a database drawn from 192peer-reviewed publications about experiments that manipulatedspecies richness and examined their effect on ecosystem processes. This global synthesis found that in areas where local species lossduring this century falls within the lower range of projections(losses of 1 to 20 percent of plant species), negligible effects onecosystem plant growth will result, and changes in species richnesswill rank low relative to the effects projected for otherenvironmental changes. In ecosystems where species losses fall within intermediateprojections of 21 to 40 percent of species, however, species lossis expected to reduce plant growth by 5 to 10 percent. The effect is comparable to the expected effects of climate warmingand increased ultraviolet radiation due to stratospheric ozoneloss. At higher levels of extinction (41 to 60 percent of species), theeffects of species loss ranked with those of many other majordrivers of environmental change, such as ozone pollution, aciddeposition on forests and nutrient pollution. "Within the range of expected species losses, we saw averagedeclines in plant growth that were as large as changes inexperiments simulating several other major environmental changescaused by humans," Hooper said. "Several of us working on this study were surprised by thecomparative strength of those effects." The strength of the observed biodiversity effects suggests thatpolicymakers searching for solutions to other pressingenvironmental problems should be aware of potential adverse effectson biodiversity as well. Still to be determined is how diversity loss and other large-scaleenvironmental changes will interact to alter ecosystems. "The biggest challenge looking forward is to predict the combinedeffects of these environmental challenges to natural ecosystems andto society," said J. Emmett Duffy of the Virginia Institute ofMarine Science, a co-author of the paper. Authors of the paper, in addition to Hooper, Cardinale and Duffy,are E. Carol Adair of the University of Vermont and the NationalCenter for Ecological Analysis and Synthesis; Jarrett Byrnes of theNational Center for Ecological Analysis and Synthesis; BruceHungate of Northern Arizona University; Kristen Matulich ofUniversity of California, Irvine; Andrew Gonzales of McGillUniversity; Lars Gamfeldt of the University of Gothenburg; and MaryO'Connor of the University of British Columbia and the NationalCenter for Ecological Analysis and Synthesis. 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