SAN FRANCISCO, May 28 (Xinhua) -- An analysis of the relationship between top predators on three different continents and the next-in-line predators they eat and compete with indicates that wolves and other top predators need large ranges to be able to control smaller predators whose populations have expanded to the detriment of a balanced ecosystem.
The findings, published in Nature Communications, were similar across continents, showing that as top predators' ranges were cut back and fragmented, they were no longer able to control smaller predators.
"Our paper suggests it will require managing for top predator persistence across large landscapes, rather than just in protected areas, in order to restore natural predator-predator interactions," co-author Aaron Wirsing, an associate professor at the University of Washington's School of Environmental and Forest Sciences, was quoted as saying in a news release from the university.
The researchers used bounty hunting data from all three continents to map the top predators' historical ranges, then mapped the range over time for the three smaller predators, looking to see where they overlapped. They found that top predators such as wolves and dingoes could suppress coyotes, red foxes and jackals only when the top predators lived at high densities and over large areas.
In addition, wolves and dingoes exert the most control closest to the core of their geographic range.
In places like Yellowstone and eastern Washington and Oregon in the United States, smaller wolf populations are too far removed from the remaining core of the species' distribution to really make a difference in controlling coyote numbers. Fewer wolves aren't the only reason coyotes have proliferated everywhere in North America. Coyotes are generalists that can live almost anywhere and have basically followed humans, eating human food and, in some cases, household pets.
"Coyotes have essentially hitched a ride with people," Wirsing noted. "Not only do we subsidize coyotes, but we also helped them by wiping out their predators -- wolves."
Gray wolves historically lived across vast swaths of North America, particularly in the western U.S. states and Canadian provinces. Coyotes, a smaller predator kept in check by wolves, appear to have been scarce in areas once dominated by wolves. As human development shrank territories for wolves, however, the wolf populations became fragmented and wolves no longer had the numbers or space to control coyotes, whose populations in turn grew.
The same story is at play in Europe and Australia, where the researchers examined the relationship between gray wolves and golden jackals, and dingoes and red foxes, respectively. As with America, when the top predator's range was slashed, the second-tier predators ballooned and ecosystems became imbalanced.
"This research shows that apex predators like dingoes and wolves need large, continuous territories in order to effectively control the balance of their ecosystems," said lead author Thomas Newsome of Deakin University and the University of Sydney in Australia. "Humans need a greater tolerance of apex predators if we want to enjoy the environmental benefits they can provide."
The researchers plan to test whether similar patterns occur for other species pairs that compete strongly.