New report warns food chain could unravel if predator numbers keep declining

July 24, 2011 – WASHINGTON — Take away the predators at the top of the food chain — the lions, tigers, wolves and cougars — and entire ecosystems start to change. A paper in today’s edition of the journal Science suggests that humans’ destruction of these top predators is causing reverberations worldwide in ways not apparent even a decade ago, including changes in the landscape and even increases in wildfires. Although the idea that there are serious ecosystem consequences to the removal of top predators isn’t new, with this paper, “it’s come of age,” says Aaron Wirsing, a professor of wildlife ecology at the University of Washington in Seattle. The review was conducted by two dozen scientists in six countries. It was funded by the National Science Foundation in the USA, Canada’s Sciences and Engineering Research Council of Canada and others. The loss of species at the top of the food chain has been happening worldwide either because humans believed they harmed livestock, competed for wild game or simply because ecosystems had become too fragmented to support them. Overfishing led to declines of sea lions, the preferred food of killer whales, and they began eating sea otters, whose populations in Alaska’s Aleutian Islands declined 90% from the late 1980s to 2005, according to the U.S. Geological Survey. Worldwide, tigers have lost 93% of their historic range, says the International Union for Conservation of Nature. In the past three decades, numbers of African lions have fallen 48.5% to fewer than 40,000, says Andrew Wetzler of the Natural Resources Defense Council. The absence of these predators creates an unpredictable cascade of effects, some of which it can take years to recognize, the researchers say. “We now live in a world, really for the first time, where these big apex consumers are missing,” says James Estes, a professor of evolutionary biology at the University of California-Santa Cruz and a lead author on the paper. –USA Today

*Lions. The destruction of lions in Africa resulted in an explosion in the baboon population. These primates carry diseases that crossed over and began infecting nearby humans.

*Wolves. When wolves were reintroduced to Yellowstone National Park, they brought down elk and deer populations, allowing creekside willows to rebound, making a more fruitful environment for species living in and near the water.

*Whales. Whales in the southern oceans dive deep to eat , then return to the surface to breathe. Their feces deposit important nutrients from the ocean bottom into the upper water layers. When populations crashed because of industrial whaling, many ocean areas become much less able to support the simple animals and plankton on which the entire ecosystem was based.  *Wildebeest. A human-introduced disease, rinderpest, almost wiped out wildebeest in parts of Africa, which in turn led to a build-up of woody vegetation, resulting in devastating wildfires. When the disease was eradicated with a vaccine, the native grasslands returned and fires calmed.

*Jellyfish: A 4-to-6-inch long fish known as the bearded goby (Sufflogobius bibarbatus) likes nothing better than a meal of jellyfish but their numbers, like sardines and tuna, have been declining from overfishing.