News / Africa

Loss of Predators Impacts Food Chain

Sharp decline upsets balance of the world’s ecosystems

Sea otters maintain kelp forests in the ocean by preying on kelp-grazing sea urchins.
Sea otters maintain kelp forests in the ocean by preying on kelp-grazing sea urchins.

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Rosanne Skirble

A loss of species at the top of the food chain could have far-reaching effects on the environment, according to a study in the Journal Science.

Some of the world’s top predators - including lions, wolves and sharks - are in sharp decline. Human activities like pollution, habitat destruction, overfishing and hunting are largely to blame.

Jim Estes studies sea otters. The University of California, Santa Cruz professor of ecology and evolutionary biology says these furry marine mammals - once hunted to near extinction - are important to the health of coastal North Pacific ecosystems.

“We have discovered that sea otters have an important limiting effect on sea urchins and that allows the kelp forest to persist," he says. "And kelp forests, in turn, have all sorts of important functions.”

In the absence of sea otters, the ocean's kelp forest - which provides a habitat for fish and absorbs climate changing carbon emissions from the atmosphere - is left barren by sea urchins.
In the absence of sea otters, the ocean's kelp forest - which provides a habitat for fish and absorbs climate changing carbon emissions from the atmosphere - is left barren by sea urchins.

The kelp forests also provide habitat for fish and absorb climate changing carbon emissions from the atmosphere. Estes says this close connection between species health and the health of global ecosystems is a “ubiquitous phenomenon and that it occurs worldwide in all ecosystem types.”

Estes compiled the work of 24 scientists in six countries. He says the research shows the cascading ecological effects of a loss of top predators and large herbivores.  

"It eventually reaches the plant populations at the base of the food web and in many instances results either in an increase in the abundance of plants or in most cases in terrestrial systems, a decrease in the abundance of plants, influencing things like fire frequency, carbon sequestration and disease and on and on and on.”

Restoration of wolves to Yellowstone National Park has allowed vegetation to recover from over-browsing by elk. Photo on left taken in 1997, on right in 2001.
Restoration of wolves to Yellowstone National Park has allowed vegetation to recover from over-browsing by elk. Photo on left taken in 1997, on right in 2001.

Estes says an example from East Africa’s Serengeti plain shows the ripple effect of rinderpest disease on the plant-eating wildebeest and the growth of a more fire-prone landscape. “The disease, by reducing the abundance of these large animals, causes the vegetation to increase, thus increasing the intensity and frequency of wildfire.”

Yet ecosystems do recover. When rinderpest was eradicated in the 1960s, the wildebeest and other hoofed species bounced back. The shrub lands were grazed back to grasslands again, reducing the potential for lightning-sparked fires.   

Elsewhere in Africa, the loss of lions, leopards, wild dogs and hyenas has allowed baboons to increase in number, which, Estes says, has created another set of problems.  

“The increasing baboon populations have spread into areas of increased human contact that has enhanced the frequency of intestinal parasites in both the baboons and in people because of the overlap of these two species now.”

Estes says the study’s findings - observed across many different ecosystems - suggest that restoring and protecting predator species will require large-scale conservation efforts.  

“To the degree that these large animals are important in maintaining biodiversity, large tracks of land or ocean are going to be required to maintain viable populations of these large consumers," he says. "And so, I think that it bears very strongly on how we look to the future for how we are going to design conservation strategies.”

Estes says the evidence is clear that saving top predator species helps preserve the world’s ecosystems. What is also clear, his research paper concludes, is that the continuing loss of these animals is “arguably humankind’s most pervasive influence on the natural world.”

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