Wolves and mountain lions could be poised to invade densely-populated cities in the United States, experts fear.
Colonies of coyotes have already established themselves in the suburbs of Chicago.
Scientists believe other potentially dangerous wild animals including wolves, lions and bears may soon be following in their footsteps as they adapt to urban living.
Mountain lions have been sighted on the fringes of American cities, with one shot near the Wrigleyville neighbourhood of Chicago.
Dr Stan Gehrt, of Ohio State University, said: "The coyote is the test case for other animals. Racoons, skunks, foxes - they've already been able to penetrate the urban landscape pretty well. The coyote is the most recent and largest. The jury's out with what's going to happen with the bigger ones. They are going to be an even bigger challenge."
For at least six years, one small coyote community five miles from Chicago's O'Hare International Airport has remained within a territory covering just a third of a square mile.
"That's an indication that they don't have to go far to find food and water," said Dr Gehrt, who has been tracking the wild dogs. "They're finding everything they need right there, in the suburbs of Chicago. It amazes me."
He estimates that about 2,000 coyotes live in the city's metro area, along with nine million people in 250 municipalities. People living in urban areas are going to have to get used to predators on their doorstep, Dr Gehrt said.
He added: "It used to be rural areas where we would have this challenge of coexistence versus conflict with carnivores. In the future, and I would say currently, it's cities where we're going to have this intersection between people and carnivores.
Dr Gehrt issued his warning at the EcoSummit 2012 meeting taking place in Columbus, Ohio. Coyotes can be helpful by hunting rodents and rabbits, but will also eat the occasional cat or small dog, he said. The animals do not usually attack humans.