In the mid-1990s, officials at Yellowstone National Park released gray wolves from areas in Canada and Montana into the park; it had been more than half a century since the predators last roamed the park. Researchers tracking the revolutionary experiment published results that they say point to the reintroduction’s role in revitalizing the once-degraded ecosystem, with the wolves’ predatory behavior indirectly supporting the growth of vegetation and even improving the health of the park’s waterways. But a heated debate rages on concerning the effects the wolves had on their environment, especially relative to roles of other members of Yellowstone’s rich carnivore community.
Yellowstone, Wyoming, US
41 gray wolves reintroduced in the mid-1990s
Following wolf reintroduction, elk numbers dropped dramatically—from nearly 20,000 in 1994 to just 8,300 in 2000—but wolves are likely not the only carnivore that contributed to that decline; black bear, grizzly, and cougar populations surged around the time of the wolf reintroduction.
Ecologists first posited that by keeping elk away from streams, wolves were indirectly allowing aspen trees to flourish. Although the trees increased in height in certain areas, their overall abundance changed little.
Although they suffer less browsing pressure since the predator increases in the 1990s, willows have not fully recovered, according to some researchers. And without willows, the recovery of streams has been limited.
Initial studies proposed that elk stay away from streamside areas where they could more easily fall prey to wolves, but new research suggests that elk only avoid these regions in the morning and at dusk. The herbivores also appear to have altered their behavior to avoid cougar-patrolled forested areas at night.
PLANNING FOR FUTURE REINTRODUCTIONS
The release of predators into the wild is controversial, and for years Yellowstone remained one of the only sites of such a bold reintroduction. But now, similar efforts are in the works around the world. In the Iberá wetlands of Argentina, for example, conservationists will soon release their first jaguars, and hypothesize that a variety of ecological changes will occur across the landscape. And in Mozambique’s Gorongosa National Park, where a reintroduction project involving wild dogs and leopards is ongoing, a study is underway using state-of-the-art tools to track the predators’ ecological effects.
Five jaguars to be reintroduced in 2020/2021
Researchers expect numbers of deer and capybaras, the jaguars’ prey, to drop once the cats are reintroduced. By reconfiguring capybara population structure, the jaguars might reduce the spread of mange between the rodents.
Ecologists suspect that the capybaras’ behavior will change in response to the presence of the jaguars, becoming more vigilant and cautious. If the capybaras spend more time watching for predators than eating, that could allow grassy vegeta-tion to flourish in certain areas.
Jaguars could kill or change the behavior of local foxes and in doing so indirectly boost numbers of the endangered birds that the foxes are known to eat.
Ecologists hypothesize that the jaguars’ presence could increase the abundance of certain scavenger species such as vultures and enhance the diversity of beetles that live off carcasses left behind by the predators.
Gorongosa National Park, Mozambique
Dozens of African wild dogs introduced in 2018/2019; leopard reintroductions slated for 2021
Scientists plan to use high-resolution satellite imagery—including LiDAR, which captures the height of trees and grasses—to assess changes in vegetation structure.
Researchers will be analyzing antelope scat using fecal DNA barcoding, alongside studies of the predators’ feces, to track the animals’ diets.
Ecologists are using GPS collars and camera-trap data to monitor the behavior of different antelope species.
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