The loss of large predators and apex consumers at the top of the food chain has caused pervasive disruption to ecosystems planetwide.
A paper published in this week's Science, a peer-reviewed academic journal, reports the findings of an international team of scientists who concluded the loss of apex consumers is arguably humankind's most pervasive influence on the natural world.
Lead author James Estes points out that apex consumers were once ubiquitious and determined the composition and dynamics of ecosystems. Without them, the plants and animals on the lower ranks of the food chain overpopulate in ways that the ecosystems cannot support.
The removal of predators like sharks and sea otters, bass and wolves has consequences, said David Garrison, director of NSF's Biological Oceanography Program, not only for these species, but for all of us.
These consequences include unfavorable changes in soil, water, vegetation, and the atmosphere. Ecosystem disruption that results from large predator decline also increases human contact with invasive and disease-carrying species.
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.
Naturally, humans are largely to blame for the decline in large predators all over the globe: Poachers and hunters have eliminated a considerable segment of apex consumers, and habitat fragmentation has further compromised the population of large predators.
The researchers pointed out that the dramatic effect on the ecosystem from the loss of large predators is not fully appreciated or understood. One explanation is that the effects are difficult to observe - large animals do not lend themselves to study in an isolated lab setting.
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 provided several examples of ecosystem damage - below are a few of those:
* Industrial whaling in the 20th century resulted in the loss of large numbers of plankton-consuming great whales, which are now known to sequester carbon into the deep sea through deposition of feces. The result has been the transfer of approximately 105 million tons of carbon into the atmosphere that would have been absorbed by whales, contributing to climate change.
*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 decline of lions and leopards from areas of sub-Saharan Africa caused a swell in the baboon population, which in turn increased transmission of intestinal parasites from baboons to humans as the primates were forced to forage closer to human settlement.
Estes has specialized in the study of coastal ecosystems for decades. In 2008, he and co-author John Terborgh of Duke University organized a conference on' trophic cascades', which are defined as a chain of effects moving down through lower levels of the food chain.
To the extent that conservation aims to restore functional ecosystems, the reestablishment of large animals and their ecological effects is fundamental, Estes said.
[Source: National Science Foundation]