"Trophic Downgrading of Planet Earth," a review paper that will be published on July 15, 2011, in the journal Science, concludes that the decline of large predators and herbivores in all regions of the world is causing substantial changes to Earth's terrestrial, freshwater, and marine ecosystems. The paper claims that the loss of apex consumers from ecosystems "may be humankind's most pervasive influence on nature."
The research was funded primarily by the Institute for Ocean Conservation Science at Stony Brook University with support from The Pew Charitable Trusts. The paper is co-authored by the Institute's executive director, Dr. Ellen K. Pikitch, and the lead author is Dr. James A. Estes, professor of ecology and evolution at the University of California at Santa Cruz.
The review, conducted by an international team of 24 scientists, illuminates the patterns and far-reaching impacts of predation and herbivory on the structure and dynamics of global ecosystems. The researchers relied on both experimental and observational evidence, which provides a strong basis for their conclusions.
"By looking at ecosystems primarily from the bottom up, scientists and resource managers have been focusing on only half of a very complex equation," said Dr. Estes. "These findings demonstrate that top consumers in the food web are enormous influencers of the structure, function, and biodiversity of most natural ecosystems."
Apex consumers include animals such as big cats, wolves, bison, sharks, and great whales, and are typically large, long-lived, and not amenable to laboratory experiments. As a result, the effects of removing them from ecosystems are not easy to document. The team of scientists reviewed an accumulation of theoretical and empirical evidence on how the decline of top predators and herbivores has affected Earth's ecosystems on land, in freshwater, and in the ocean. Their findings suggest that "trophic downgrading" -- the ecological consequences of losing large apex consumers from nature -- causes extensive cascading effects in ecosystems worldwide, especially when exacerbated by factors such as land use practices, climate changes, habitat loss, and pollution.
"Our review of existing studies clearly shows that a top-down cascading effect in natural systems is both powerful and widespread," said Dr. Estes. "There is an urgent need for interdisciplinary research to forecast how a continued loss of top level consumers will further harm the planet's ecosystems."
This paper documents some of the negative effects that the widespread loss of these animals has already had on Earth's biosphere, climate, biodiversity, and vegetation:
"We must assume going forward that significant changes to the ecosystem are occurring when large predators and herbivores are removed from the top of the food web, and, thus, that efforts to manage and conserve nature must include these animals," said Dr. Pikitch. "An old paradigm has shifted, and those who question this theory now have the burden to prove otherwise."
Materials provided by Stony Brook University. Note: Content may be edited for style and length.
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