Large Predators Are Critical to the Stability of Our Natural Areas

This is a guest post from Dr. James A. Estes, a professor in the Department of Ecology and Evolutionary Biology at the University of California, Santa Cruz.

In a world containing some 10 million or more species, the current tide of extinction cannot be stemmed one species at a time. More general strategies are needed. Nearly everyone understands this fundamental truth. But what are these strategies? Although the devil is in the details, the answer in the minds of most conservation thinkers and planners hinges on a single key factor—habitat. All species require habitat to survive and reproduce. Preserve enough habitat in the right places and species preservation will follow. The problem is that this strategy isn’t working very well. We continue to loose species, even from the largest conservation areas. So what’s the problem? It might be that the strategy is fine but we have yet to get the details right—enough habitat with sufficient protection in the right places. Or it might be that something more is needed.

Our argument is this. Large apex consumers–creatures like lions, wolves, bears and killer whales–are key elements of nature. Virtually all habitats have had them for millions of years. That is, until recently.

On 13 July, 2011, I coauthored a review in the journal Science with 23 other ecologists from around the world in which we argue that something more is indeed needed. That something is the apex consumers. Our argument is this. Large apex consumers–creatures like lions, wolves, bears and killer whales–are key elements of nature. Virtually all habitats have had them for millions of years. That is, until recently. These large apex consumers have been among the first species to disappear from our increasingly human-dominated world. And along with the loss of these animals has been the loss of something even more fundamental—the essential roles they play in holding their ecosystems together.  We are beginning to see these roles nearly everywhere—from the tropics to the poles, and on land, in rivers and lakes, and in the sea.

Our review details the theoretical basis for this phenomenon and provides many specific examples. My favorite example is the link between sea otters and coastal ecosystems in the North Pacific Ocean. The loss of otters has led to population irruptions of their prey—sea urchins. Hyperabundant urchins overgraze kelp forests, leading in turn to reductions or the loss of species and ecosystem services that depend on kelp forests. Similarly, the loss of wolves, grizzly bears and cougars from much of North America has led to population irruptions of their prey—moose, elk and deer—which in turn have overgrazed their range, thus leading to the loss of both plant species and the animals that depend on these plants. In another well known example, the loss of coyotes from chaparral fragments in southern California has allowed these habitats to be invaded by “mesopredators”–cats, foxes, and other small carnivore–that in turn have caused the extinction of birds and other small vertebrates. The list goes on and on. These are not unique stories but examples of a global phenomenon. And the effects of apex consumers extend widely across ecosystems to influence such diverse phenomena as wildfire, disease, and air and water quality. Trophic downgrading, which begins with the loss of large apex consumers from nature, can be thought of as an ecological chain reaction that is part and parcel to the biodiversity crisis.

What does this mean to wildlife conservation? It means that while habitat is essential, by itself habitat conservation is not enough to conserve biodiversity.

What does this mean to wildlife conservation? It means that while habitat is essential, by itself habitat conservation is not enough to conserve biodiversity. This in turn has several obvious implications for conservation planning. Small conservation areas are doomed to fail, or at least doomed to be much less than they might otherwise be because small areas are incapable of maintaining viable populations of large, apex consumers. Even large conservation areas are doomed to under-perform unless they also contain the apex consumers.

The bottom line for conservation is simply this. Habitat is necessary but insufficient for biodiversity conservation. Apex consumers are also required to run nature’s engine.

Read Defenders of Wildlife’s original blog piece on the paper and learn more about our work with apex predators.

Read The Nature Conservancy’s blog that talks about the paper and what impacts it can have on conservation.

The following six videos are interviews with Jim Estes, in which he talks about how the paper came to be, the implications on policy makers, and  other insights from the research paper.  The videos are in a playlist and after you watch the first you may scroll through the rest from the same location.

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- who has written 1 posts on dotWild.

Jim Curland is the Marine Program Associate for Defenders of Wildlife. Jim advocates for sea otters, other marine species and marine habitat conservation at the federal, state and local levels.

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One Response to “Large Predators Are Critical to the Stability of Our Natural Areas”

  1. David Kane says:

    The undeniable role of apex predators can’t be argued against. The issue that remains is that the continually growing and resource-consuming human population continues to put pressure on ecosystems in which we inhabit. That pressure isn’t being reduced, and won’t be in the near future so long as the Western world and China continue to aspire to a certain high-level lifestyle, and subsequently creates that desire among impoverished people throughout the globe. Shrinking habitat the world-over will continue to be the driving force that will make establishing intact ecosystems a continually daunting task.

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