UC Santa Cruz professor’s paper examines predator influence on ecosystems

 

UC Santa Cruz professor’s paper examines predator influence on ecosystems

 

Posted 15 July 2011, by Tovin Lapan, Mercury News (Bay Area News Group (Media News Group)), mercurynews.com

 

SANTA CRUZ — Sea otters, which can often be seen in Monterey Bay belly up floating on the surface of the ocean munching on mollusks, may look like they spend most of their time lounging.

But the furry marine mammals provide a vital service to marine ecology, they feast on urchins that, if left unchecked, would decimate the nutrient-rich kelp forests.

The decline in population of animals at the top of the food chain, such as sea otters, has had profound and disruptive impacts on ecosystems all over the world a recent study found.

UC Santa Cruz professor of ecology and evolutionary biology James Estes was lead author for the paper, published Friday in the weekly “Science.” The study drew on the research of scientists around the world to show the effects of diminishing numbers of large predators and other animals at the top-rung of the food chain known as apex consumers on terrestrial, freshwater and marine ecosystems.

“The loss of apex consumers is arguably humankind’s most pervasive influence on the natural world,” the study concluded.

The decline of apex consumers has had wide ranging effects, from changing vegetation, wildfire frequency, infectious disease, invasive species, water quality and nutrient cycles, Estes’ own research focuses on sea otters and orcas.

“Sea otters have a strong and direct effect on kelp forests,” he said. “Otters feed on sea urchins, which feed on kelp. Without the otters the urchins mow down

the kelp forest. That in turn has a wide array of effects on coastal ecosystems, including causing a decline in fish populations that feed on the kelp.” The paper’s co-authors include 24 scientists from six countries who offered their insights into the animals at the top of the food chain or apex consumers they study.

In Yellowstone National Park the local extinction of wolves led to elk over-browsing on willow and aspen. The restoration of wolves in the park allowed the vegetation to recover.

The diminished populations of lions and leopards in parts of Africa led to an increase in the population of olive baboons. The baboons had increased contact with humans which resulted in higher rates of intestinal parasites in both humans and baboons.

In 2008, Estes and one of the paper’s co-authors, John Terborgh of Duke University, organized a conference on trophic cascades, the phenomenon that occurs when impacts at the top of the food chain lead to various effects on lower levels of the food chain.

At the end of the conference Estes and his peers agreed that they needed to synthesize the findings of the gathered ecologists from around the world into one paper.

“The breadth of the effects these animals have on nature, that’s what was really the surprise,” Estes said.

As an example, he pointed to one study mentioned in the article that analyzed how an African rinderpest epidemic from the first part of the 20th century caused changes in vegetation and wildfire frequency.

The epidemic decimated wildebeest and other hoofed-animal populations in the Serengeti, which led to a wider growth of woody vegetation and stronger and more frequent wildfires. The rinderpest was eradicated in the 1960s and the area returned to its former state over time.

For many of the cases cited the decline in the apex consumer population was linked to human activity, such as hunting and habitat fragmentation, when the previously large swaths of land that the animals roam are diminished by human encroachment.

The study has implications for conservation efforts for large predators and other animals at the top of the food chain.

“My interest from this point on is to apply these finding to conservation and resource management,” Estes said. “These animals roam over large areas, and will need large-scale approaches to conservation.”

 

http://www.mercurynews.com/science/ci_18487240

 

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