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. But there have also been dramatic declines in populations of many large herbivores, such as elephants and bison. The decline of apex consumers has been most pronounced among the big predators, such as wolves and lions on land, whales and sharks in the oceans, and large fish in freshwater ecosystems. Their decline, largely caused by humans through hunting and habitat fragmentation, has had far-reaching and often surprising consequences, including changes in vegetation, wildfire frequency, infectious diseases, invasive species, water quality, and nutrient cycles. The study looked at research on a wide range of terrestrial, freshwater, and marine ecosystems and concluded that "the loss of apex consumers is arguably humankind's most pervasive influence on the natural world."Īccording to first author James Estes, a professor of ecology and evolutionary biology at the University of California, Santa Cruz, large animals were once ubiquitous across the globe, and they shaped the structure and dynamics of ecosystems. The decline of large predators and other "apex consumers" at the top of the food chain has disrupted ecosystems all over the planet, according to a review of recent findings conducted by an international team of scientists and published in the July 15 issue of Science.
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