July 19th, 2011 by Joshua S Hill
“The loss of apex consumers is arguably humankind’s most pervasive influence on the natural world,” argue the authors of a new report published in the journal Science, which looked at the decline of large predators and other ‘apex consumers’ at the top of the food chain.
The study looked at the massive decline of apex predators – animals such as wolves, lions, sharks and sea otters – and the subsequent impact on the ecosystems those animal once lived in.
James Estes, professor of ecology and evolutionary biology at the University of California, Santa Cruz, notes that large animals were once ever-present across the globe, shaping their environments and affecting every level from the top down. Their subsequent decline, either as a result of human hunting or habitat fragmentation caused by the spread of humans, has left far-reaching and often surprising consequences, including changes in vegetation, wildfire frequency, infectious diseases, invasive species, water quality, and nutrient cycles.
The loss of animals – both predators like the lion and wolves on land, whales and shakrs in the oceans, and herbivores like bison and elephant – has caused an ecological phenomenon known as a “trophic cascade”; a chain of effects that move down through the 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.”
Estes and his coauthors cite a wide range of examples in their review, including the following:
- The extirpation of wolves in Yellowstone National Park led to over-browsing of aspen and willows by elk, and restoration of wolves has allowed the vegetation to recover.
- The reduction of lions and leopards in parts of Africa has led to population outbreaks and changes in behavior of olive baboons, increasing their contact with people and causing higher rates of intestinal parasites in both people and baboons.
- A rinderpest epidemic decimated the populations of wildebeest and other ungulates in the Serengeti, resulting in more woody vegetation and increased extent and frequency of wildfires prior to rinderpest eradication in the 1960s.
- Dramatic changes in coastal ecosystems have followed the collapse and recovery of sea otter populations; sea otters maintain coastal kelp forests by controlling populations of kelp-grazing sea urchins.
- The decimation of sharks in an estuarine ecosystem caused an outbreak of cow-nosed rays and the collapse of shellfish populations.
“We now have overwhelming evidence that large predators are hugely important in the function of nature, from the deepest oceans to the highest mountains, the tropics to the Arctic,” said William Ripple, a professor of forestry at Oregon State University, co-author of the report.
“In a broad view, the collapse of these ecosystems has reached a point where this doesn’t just affect wolves or aspen trees, deforestation or soil or water. These predators and processes ultimately protect humans. This isn’t just about them, it’s about us.”
Such a study as this provides profound implications for conservationists. “To the extent that conservation aims toward restoring functional ecosystems, the reestablishment of large animals and their ecological effects is fundamental,” Estes said. “This has huge implications for the scale at which conservation can be done. You can’t restore large apex consumers on an acre of land. These animals roam over large areas, so it’s going to require large-scale approaches.”
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