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 new wide-ranging review published this month in the journal Science. A team of 24 scientists from six countries analyzed 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."
The authors cite a wide range of examples in the review including a well-documented case where the decimation of sharks in an estuarine ecosystem caused an outbreak of cow-nosed rays and a subsequent collapse of shellfish populations.
Despite this and other well-known examples, the extent to which ecosystems are shaped by such interactions has not been widely appreciated. One reason for this is that 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," James Estes, first author of the review, 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 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."
Learn more about the importance of apex predators to the marine ecosystem: Threats – Predator Loss