Editor’s note: The views expressed here are Peter Kareiva’s and should not be taken as the position of The Nature Conservancy.
Conservation folklore has it that losing a species creates a cascade of negative effects for an ecosystem, tearing at its delicate web of life. Data tell a different story. Usually, species loss creates minimal impacts on how well an ecosystem functions, unless we’re talking about the loss of many species — say, 50% of a given ecosystem.
But there are some species whose removal alters their ecosystem so drastically that even the most casual observer can see the difference. Most typically, these species are what scientists call “apex consumers” (also known as “apex predators”) — species that exist at or near the top of their food chains, such as wolves, sharks, bears, foxes and sea otters. The loss of so-called “megaherbivores” such as wildebeest and elephants can also have dramatic effects.
But while ecologists have long known that apex consumers and megaherbivores are special, biodiversity conservation has rarely given them special attention. Why the neglect? Because protecting biodiversity is often turned into a “number of species” game — save the places with the most species. However, all species are not created equal — and it is wrong to invest equally in all species.
A path-breaking article just published in Science may change all that. Two dozen of the world’s leading ecological scientists have synthesized their career knowledge studying apex consumers. The result is a tour de force, and the message for conservation is clear: Biodiversity loss in the abstract and numerical sense is NOT the problem. Biodiversity has been depleted before and then recovered. Similarly, it is being depleted now and will likely recover again. The problem is that the extinction process being driven by humans today is targeting apex consumers and megaherbivores, and thus is a much bigger deal than some “percent decline in biodiversity.”
In the article, Jim Estes and his dream team of star ecologists examine nine case studies in which the effects of losing top consumers are depicted via a series of photographic contrasts: with and without the apex consumer. These pictures are astonishing in how vividly they display altered ecosystems. Of course, they also present detailed measurements of ecosystem change, but the photos speak volumes about the magnitude and extent of the effects. Without these large top predators, rates of infectious disease, wildfires, and carbon emissions can skyrocket. Losing them can also cause degradation in vegetation, water quality and nutrient cycles, according to the authors.
Take one example from Yellowstone National Park, where eliminating wolves led to an explosion in the elk population, which then feasted on trees such as willows and aspen that shaded the park’s rivers. The lack of trees led to declines in species that lived in or along the rivers, such as beavers, birds and fish. Reintroducing wolves to Yellowstone, conversely, allowed these species to recover, and full ecosystem function to return.
Conservation has rallied around many different goals: lands and waters, zero extinction, biodiversity hotspots, charismatic species, and (most recently) ecosystem services. It is a mistake to think there is any one goal for conservation, because goals are human choices — they might be informed by science, but in the end they reflect human values and preferences. To the extent that science does inform our conservation goals, the article by Jim Estes makes a compelling case for making the protection and restoration of apex consumers one of our highest priorities.
Imagine a new conservation NGO with the goal of protecting or restoring the apex consumers in all of the world’s major ecosystem types — so that at least one representation of every ecosystem or habitat type had its full complement of apex consumers. That conservation goal would be easy to track and observe progress (unlike the Convention on Biodiversity’s goal of “slowing the rate of biodiversity loss,” which is problematic to measure, scientifically dicey, and has thus far been impossible to achieve). The goal would inevitably lead to large intact ecosystems. The goal could still accommodate human activities (witness the reintroduction of wolves and grizzly bears into the Great Yellowstone ecosystem). And the goal would inspire many. Can conservation claim as much for its current goals? And do we have such iconic species to define and promote what we are trying to accomplish?
I know that apex consumers aren’t the only things conservation needs to be concerned with. But the article by Jim Estes and colleagues should lead us to give more resources and explicit attention to protecting and restoring these species. They are the next best thing to a holy grail for our work.
(Image: Wolf at Yellowstone Grizzly and Wolf Discovery Center. Image credit: WSK_2005/Flickr through a Creative Commons license.)
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