When the top animals in the food chain vanish, the food chain itself changes in often unpleasant ways.

Overfishing of top predators such as sharks and tuna means more nasty, stinging jellyfish. Where wolves are hunted into extinction, more wily coyotes arrive.

These second-banana predators, or "mesopredators," are proving harder for humans to handle than the original top predators, according to a study published recently in the journal Bioscience.

In North America, all of the largest land predators have been on the decline during the past 200 years, according to the study, performed by researchers from Oregon State University, UC Berkeley and New Mexico State University at Las Cruces. Meanwhile, the ranges of 60 percent of mesopredators have expanded.

Mesopredators are not only smaller, but more numerous than top predators, and usually more fertile, a pattern found down the food chain. While it has been easy for humans to exterminate wolves from areas, coyotes are tougher customers.

"The economic impacts of mesopredators should be expected to exceed those of apex predators in any scenario in which mesopredators contribute to the same or to new conflict with humans," the researchers write in their report. "Mesopredators occur at higher densities than apex predators and exhibit greater resiliency to control efforts."

Without wolves to keep coyotes in check, the coyote population rises, and these adaptable creatures have taken to living in suburbs and cities. There, coyotes feast on another mesopredator: cats, domestic and feral. Cats prey on smaller animals, such as birds and rats, which prey on bugs.

The study found that mesopredators are more disruptive to humans than apex predators. While apex predators are usually carnivores, mesopredators are often omnivores, and will eat crops and damage other plants important to humans.

In nature, this web of predator-prey relationships maintains a self-regulating balance, with the predator population rising or falling in sync with their prey. When the top predator is removed, the entire chain is upset, with disturbing consequences for urbanites in cities and ranchers in the countryside.

While wolves kill sheep, they also benefit ranchers by keeping the coyote population down, said William Ripple, a study author, in a news release about the research. Without wolves, coyote depredations of sheep and pronghorn antelope have exploded.

"These problems resist simple solutions," Ripple said in the release. "I've read that when Gen. George Armstrong Custer came into the Black Hills in 1874, he noticed a scarcity of coyotes and the abundance of wolves. Now the wolves are gone in many places, and coyotes are killing thousands of sheep all over the West."

In the ocean, the story is similar, although the motivation is different. There, humans are hunting apex predators such as shark and tuna to eat them, not to intentionally destroy their populations. But the effect is the same, or perhaps even more noxious.

Jellyfish are usually not eaten by humans, and some species carry painful or deadly stings. Beaches around the world have experienced unusual influxes of jellyfish, whose numbers proliferate in the absence of their predators.

An Australian study released in June found that this surge in jellyfish threatens in some areas to become self-perpetuating. When fish predators are gone, jellyfish can become the dominant species in a new stable pattern. The study was published in the journal Trends in Ecology and Evolution.

The research was led by Dr. Anthony Richardson of the University of Queensland, along with colleagues at the University of Miami in Florida, Swansea University in the United Kingdom and the University of the Western Cape in South Africa.

Richardson coined a pithy phrase to describe this ascendance of the nettlesome invertebrates: the "jellyfish joyride."

Call staff writer Bradley J. Fikes at 760-739-6641. Read his blogs at bizblogs.nctimes.com.