Ecosystem restoration requires re-introduction of large predators
By Summit Voice
SUMMIT COUNTY — The loss of top predators has far-reaching ecosystem impacts, including changes in vegetation, wildfire frequency, infectious diseases, invasive species, water quality and nutrient cycles, according to a team of international scientists who studied and compared those impacts across a wide range of terrestrial, freshwater and marine ecosystems.
“The loss of apex consumers is arguably humankind’s most pervasive influence on the natural world,” and has disrupted ecosystems across the researchers concluded in their study, published last week in the journal Science.
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.
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 removal of predators like sharks and sea otters, bass and wolves has consequences, not only for these species, but for all of us,” said David Garrison, director of the National Science Foundation’s Biological Oceanography Program.
“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 co-authors cite a wide range of examples in their review, including:
• The extirpation of wolves in Yellowstone National Park led to over-browsing of aspen and willows by elk; restoration of wolves allowed the vegetation to recover.
• Dramatic changes in coastal ecosystems 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.
Despite these and other well-known examples, the extent to which such interactions shape ecosystems was not widely appreciated, scientists say.
“There’s been a tendency to see it as idiosyncratic and specific to particular species and ecosystems,” Estes said.
One reason for this is the top-down effects of apex predators are difficult to observe and study.
“These interactions are invisible unless there is some perturbation that reveals them,” Estes said. “With these large animals, it’s impossible to do the kinds of experiments that would be needed to show their effects, so the evidence has been acquired as a result of natural changes and long-term records.”
The study’s findings have profound implications for conservation.
“To the extent that conservation aims to restore 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.”
The paper’s coauthors include 24 scientists from various institutions in six countries. The Institute for Ocean Conservation Science, Defenders of Wildlife, White Oak Plantation, NSERC Canada and NordForsk provided other support for the research.