An international team of scientists 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," a release from the National Science Foundation, which helped fund the study, said.
Large animals, once ubiquitous across the globe, shaped the structure and dynamics of ecosystems, said study leader James Estes, a marine ecologist and evolutionary biologist at the University of California, Santa Cruz.
Their decline, caused in large part by human activities including hunting and habitat fragmentation, has far-reaching and often surprising consequences, he said, including changes in vegetation, wildfire frequency, infectious diseases, invasive species, water quality and nutrient cycles.
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 top-down effects of apex consumers in an ecosystem are fundamentally important, but it is a complicated phenomenon," Estes said. "They have diverse and powerful effects on the ways ecosystems work, and the loss of these large animals has widespread implications."
The study was published in the journal Science.