By Jenny Marder, PBS NewsHour
Sea otters eat sea urchins and sea urchins eat kelp. When sea otters are present, the coastal kelp forests maintain a healthy balance. But when the fur trade wiped out the otters in the Aleutian Islands in the 1990s, sea urchins grew wildly, devouring kelp, and the kelp forest collapsed, along with everything that depended on it. Fish populations declined. Bald eagles, which feed on fish, altered their food habits. Dwindled kelp supplies sucked up less carbon dioxide, and atmospheric carbon dioxide increased.
The animal that sits at the top of the food chain matters, and its loss has large, complex effects on the structure and function of its ecosystem, according to an article published on Thursday in the online issue of the journal, Science.
That the presence or loss of an ecosystem's top predator is linked to surges and crashes in the food chain is nothing new. The term for the phenomenon is "trophic cascade," and it's been applied to coastal sea otters, as well as the gray wolves in Yellowstone and the mountain lions in Zion National Park, to name just a few.
But what is new, authors of the paper say, is that this is ubiquitous across all ecosystems. "We see it on land, we see it on water, we see it in high latitudes, we see it in low latitudes," said James Estes, a research scientist at the Institute for Marine Sciences at the University of California, Santa Cruz and the paper's lead author. "We do not not see it anywhere."
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http://www.scientificamerican.com/article.cfm?id=loss-of-top-predators-ecology-changes