Restoring predator and prey at the same time is best

By Julia John

Wolves chase an elk in Yellowstone National Park. ©Doug Smith

The elk or wolf – which comes first in population management? For optimal results, according to a recent study, the answer is actually both predator and prey together.

“By managing in a holistic sense, considering the interactions between species, you recover the entire ecosystem faster and with less volatility,” said Mark Novak, assistant professor of integrative biology at Oregon State University and co-author on the paper in Nature Ecology and Evolution. “You have less population explosions and fewer crashes than when you manage species one at a time.”

Overharvesting of species through activities such as hunting and fur trading has caused many population declines and collapses, and wildlife managers have typically tried to manage them back to recovery one species at a time, Novak said. But species are connected to each other, often through predator-prey relationships. So the exploitation and management of Atlantic cod, for example, is linked to the exploitation and management of herring, a primary component of the cod diet.

Steps to ecosystem recovery typically involve reducing harvests on the prey species to establish a substantial prey base before attempting to increase predator numbers. This research suggests that limiting harvests of predator and prey simultaneously allows for faster restoration and more stable populations.

This is a fresh take on “the cadence of recovery,” Novak said.

The researchers compared existing data on the abundance of more than 50 pairs of exploited marine predator and prey species worldwide over recent years, going back to the 1970s. Their paper also considered recoveries of land-based predators and prey, such as lions and wildebeest in the Serengeti and mink and muskrat in Newfoundland.

The biologists observed that in half the cases, predator and prey didn’t recover simultaneously. However, using modeling, they discovered that populations should recover quickest and steadiest when harvest rates on predator and prey are reduced in sync.

“The order and timing of how you approach recovery does matter,” said lead author Jameal Samhouri, of NOAA’s Northwest Fisheries Science Center.

Novak agreed. “There are many populations we could be managing more effectively by managing more synchronously,” he said.

Restoring predator and prey at once could even prove economically preferable to the standard species-by-species approach, Novak said. Although people might think reducing harvest pressure on predators and prey at the same time would damage profits for individuals who derive income from wildlife, such as trappers, it may have less of an economic impact on them than the traditional approach.

The team hopes to expand upon this research to understand its relevance to smaller, endangered populations, as well as to more complex multispecies networks.

Julia John is a science writer at The Wildlife Society. Contact her at jjohn@wildlife.org with any questions or comments about her article.

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