Science

Alligators, sharks, coyotes reclaiming their old haunts. Get used to it, study says.

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Alligators and seals are showing up on Carolina beaches, great white sharks are patrolling the coast and coyotes have become a nuisance from the mountains to the Outer Banks.

Sightings of those predators are still startling enough to make news. But a study led by Duke University scientists suggests the wayward animals aren’t “lost” but simply coming home — to places they occupied before humans hunted them heavily.

And people better get used to it.

“We can no longer chock up a large alligator on a beach or coral reef as an aberrant sighting,” said Duke ecologist Brian Silliman, lead author of an essay published Monday in Current Biology magazine. “It’s not an outlier or short-term blip. It’s the old norm, the way it used to be before we pushed these species onto their last legs in hard-to-reach refuges. Now, they are returning.”

Silliman, Rachel Carson associate professor of marine conservation biology at Duke’s Nicholas School of the Environment, and his colleagues combed recent scientific papers and government papers. They found that nearly two dozen large predators — the essay calls them “consumers” — have expanded into new habitats.

It turns out that alligators in the Southeast, once thought to be most at home in freshwater, can readily tolerate saltwater as their numbers increase. Sea otters in California are moving from open water into marshes and seagrass beds. Gray wolves and mountain lions are expanding their current ranges. Coyotes and bobcats are venturing onto beaches. Killer whales have been spotted in freshwater rivers.

Those findings upend long-held ecologists’ notions, based on studies of species whose numbers were declining, that those predators require highly specific places to forage and breed, the essay says. “Those aren’t just stories on the Animal Channel but in ecology classes. I believed them,” Silliman said in an an interview.

But now that many predators are rebounding, they’re showing remarkable resilience.

Other studies have documented climate change as a driving force for some species moving northward and to higher elevations. But neither climate nor lack of competition for prey from other predators fully explain the expansion into new territory, the Duke study says.

Many predators, instead, are moving into places thought to be less hospitable to those predators. The researchers note that many large “consumers,” such as black bears and coyotes, are highly adaptable to new prey choices and habitats.

“They’re recolonizing harsher environments,” Silliman said. “Is it the case that animals are going there for their first time? Probably not.”

There are ecological benefits to predators reoccupying their old haunts, the essay notes. Sea otters returning to seagrass beds in estuaries feed on crabs that in turn eat sea slugs that eat algae. In that way, the otters indirectly keep algae from smothering the seagrass.

What does the spread of predators into their old territories mean for the humans who also live there? That they can coexist if people change old attitudes that cast predators as the boogeyman, Silliman said.

He pointed to Asheville, where the abundance of urban bears has made the beer-mad mountain town also known as Bear City. Bear sightings there are so common that residents are much more likely to shoot video than guns during encounters. Most residents are cautious about placing bird feeders or garbage cans where they’re likely to attract bears.

“The acceptable behavior of predators and humans has to change,” Silliman said. “There will be conflicts, but it can be reduced by policy and new behaviors.”

Silliman’s coauthors were Lindsay Gaskins, Qiang He and Andrew Read of Duke; Brent Hughes of the University of California Santa Cruz; Tim Tinker of UCSC and the U.S. Geological Survey; James Nifong of Kansas State University; and Rick Stepp of the University of Florida. Funding came from the Stolarz Foundation, the National Science Foundation, a David H. Smith Conservation Fellowship, the U.S. Geological Survey, and the California Coastal Conservancy

Bruce Henderson: 704-358-5051; @bhender

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