A new paper in Science by Jim Estes and colleagues reviews contemporary findings on the consequences of removing large apex consumers (e.g., top predators) from nature—a process they term trophic downgrading.
The authors highlight the ecological theory that predicts trophic downgrading, consider why these effects have been difficult to observe, and summarize the key empirical evidence for trophic downgrading. The paper concludes that “Bottom-up forces are ubiquitous and fundamental, and they are necessary to account for the responses of ecosystems to perturbations, but they are not sufficient. Top-down forcing must be included in conceptual overviewsif there is to be any real hope of understanding and managing the workings of nature.”
The full paper is available here.
[UPDATE 7/15/2011]
Some press on the Estes et al. paper:
PBS.
It’s interesting to note the contrast between the PBS article, which manages to summarize the scientific debate while not losing sight of the big picture: “Scientists don’t all agree on these mechanisms. Kauffman’s research, for example, found that the behavior of the elk has not changed significantly since the wolves returned. More important to new tree growth, he said, is that wolves are directly reducing the elk population through predation. But most scientists do agree that the influence of the presence or absence of top predators is far reaching.”
vs. the WaPost article which only interviews one of the study’s authors and which ends with perhaps the weakest example from the Estes et al. paper, an anecdote attributing deforestation of the Isle of Rum in Scotland to loss of wolves. Actually, the island was farmed intensively for sheep production for hundreds of years, and is only 40 square miles in size, one-fifth the size of Isle Royale, so might not even support a single pack of wolves, and is not a good example for effects of loss of top predators.
But aside from a few overgeneralizations such as this, the paper is very informative.