The decline of large predators and other "apex consumers" at the top of the food chain has disrupted ecosystems across the planet.
The finding is reported by an international team of scientists in a paper in this week's issue of the journal Science.
The study looked at research results from a wide range of terrestrial, freshwater and marine ecosystems and concluded "the loss of apex consumers is arguably humankind's most pervasive influence on the natural world."
According to lead author James Estes, a marine ecologist and evolutionary biologist at the University of California, Santa Cruz, large animals were once ubiquitous across the globe. They shaped the structure and dynamics of ecosystems.
Their decline, largely caused by humans through hunting and habitat fragmentation, has far-reaching and often surprising consequences, including changes in vegetation, wildfire frequency, infectious diseases, invasive species, water quality and nutrient cycles.
Plummeting numbers of apex consumers are most pronounced among the big predators, such as wolves on land, sharks in the oceans, and large fish in freshwater ecosystems. There also are dramatic declines in populations of many large herbivores, such as elephants and bison.
The loss of apex consumers from an ecosystem triggers an ecological phenomenon known as a "trophic cascade," a chain of effects moving down through lower levels of the food chain.
The research, funded in part by the National Science Foundation (NSF), "highlights the unanticipated effects of trophic cascades on Earth systems, including far-reaching processes such as biogeochemical cycles," said David Garrison, director of NSF's Biological Oceanography Program.
"The removal of predators like sharks and sea otters, bass and wolves has consequences," said Garrison, "not only for these species, but for all of us."
"The top-down effects of apex consumers in an ecosys
|Contact: Cheryl Dybas|
National Science Foundation