Loss of biodiversity appears to affect ecosystems as much as climate
change, pollution and other major forms of environmental stress,
according to results of a new study by an international research team.
The study is the first comprehensive effort to directly compare the
effects of biological diversity loss to the anticipated effects of a
host of other human-caused environmental changes.
The results, published in this week's issue of the journal
Nature,
highlight the need for stronger local, national and international
efforts to protect biodiversity and the benefits it provides, according
to the researchers, who are based at nine institutions in the United
States, Canada and Sweden.
"This analysis establishes that reduced biodiversity affects
ecosystems at levels comparable to those of global warming and air
pollution," said Henry Gholz, program director in the National Science
Foundation's Division of Environmental Biology, which funded the
research directly and through the National Center for Ecological
Analysis and Synthesis.
"Some people have assumed that biodiversity effects are relatively
minor compared to other environmental stressors," said biologist David
Hooper of Western Washington University, the lead author of the paper. "Our results show that future loss of species has the potential to
reduce plant production just as much as global warming and pollution." Studies over the last two decades demonstrated that more biologically diverse ecosystems are more productive.
Until now, it's been unclear how biodiversity losses stack up
against other human-caused environmental changes that affect ecosystem
health and productivity.
"Loss of biological diversity due to species extinctions is going to
have major effects on our planet, and we need to prepare ourselves to
deal with them," said ecologist Bradley Cardinale of the University of
Michigan, one of the paper's co-authors. "These extinctions may well
rank as one of the top five drivers of global change."
In the study, Hooper, Cardinale and colleagues combined data from a
large number of published studies to compare how various global
environmental stressors affect two processes important in ecosystems:
plant growth and the decomposition of dead plants by bacteria and fungi. The study involved the construction of a database drawn from 192
peer-reviewed publications about experiments that manipulated species
richness and examined their effect on ecosystem processes.
This global synthesis found that in areas where local species loss
during this century falls within the lower range of projections (losses
of 1 to 20 percent of plant species), negligible effects on ecosystem
plant growth will result, and changes in species richness will rank low
relative to the effects projected for other environmental changes.
In ecosystems where species losses fall within intermediate
projections of 21 to 40 percent of species, however, species loss is
expected to reduce plant growth by 5 to 10 percent. The effect is comparable to the expected effects of climate warming
and increased ultraviolet radiation due to stratospheric ozone loss. At higher levels of extinction (41 to 60 percent of species), the
effects of species loss ranked with those of many other major drivers of
environmental change, such as ozone pollution, acid deposition on
forests and nutrient pollution.
"Within the range of expected species losses, we saw average
declines in plant growth that were as large as changes in experiments
simulating several other major environmental changes caused by humans,"
Hooper said. "Several of us working on this study were surprised by the comparative strength of those effects."
The strength of the observed biodiversity effects suggests that
policymakers searching for solutions to other pressing environmental
problems should be aware of potential adverse effects on biodiversity as
well. Still to be determined is how diversity loss and other large-scale environmental changes will interact to alter ecosystems. "The biggest challenge looking forward is to predict the combined
effects of these environmental challenges to natural ecosystems and to
society," said J. Emmett Duffy of the Virginia Institute of Marine
Science, a co-author of the paper.
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Authors of the paper, in addition to
Hooper, Cardinale and Duffy, are E. Carol Adair of the University of
Vermont and the National Center for Ecological Analysis and Synthesis;
Jarrett Byrnes of the National Center for Ecological Analysis and
Synthesis; Bruce Hungate of Northern Arizona University; Kristen
Matulich of University of California, Irvine; Andrew Gonzales of McGill
University; Lars Gamfeldt of the University of Gothenburg; and Mary
O'Connor of the University of British Columbia and the National Center
for Ecological Analysis and Synthesis.
