By CORNELIA DEAN

Human actions are increasing the rate of evolutionary change in plants and animals in ways that may hurt their long-term prospects for survival, scientists are reporting.

Hunting, commercial fishing and some conservation regulations, like minimum size limits on fish, may all work against species health. The idea that target species evolve in response to predation is not new. For example, researchers reported several years ago that after decades of heavy fishing, Atlantic cod had evolved to reproduce at younger ages and smaller sizes.

Based on an analysis of earlier studies of 29 species? mostly fish, but also a few animals and plants like bighorn sheep and ginseng? researchers from several Canadian and American universities found that rates of evolutionary change were three times higher in species subject to“harvest selection”than in other species. Writing in The Proceedings of the National Academy of Sciences, the researchers say the data they analyzed suggested that size at reproductive maturity in the species under pressure had shrunk in 30 years or so by 20 percent, and that organisms were reaching reproductive age about 25 percent sooner.

In Alberta, Canada, for example, where regulations limit hunters of bighorn sheep to large animals, average horn length and body mass have dropped, said Paul Paquet, a biologist at the University of Calgary who participated in the research. And as people collect ginseng in the wild,“the robustness and size of the plant is declining,”he said.

The researchers said that reproducing at a younger age and smaller size allowed organisms to leave offspring before they were caught or killed. But some evidence suggests that they may not reproduce as well, said Chris Darimont, a postdoctoral fellow in environmental studies at the University of California, Santa Cruz, who led the work. The fish they studied that are reproducing earlier“on average have far,far,far fewer eggs than those who wait an additional year and grow a few more centimeters,”he said .

The researchers also noted that the pattern of loss to human predation like hunting or harvesting is opposite to what occurs in nature or even in agriculture.

Predators typically take“the newly born or the nearly dead,”Dr.Darimont said. For predators, targeting healthy adults can be dangerous, and some predator fish cannot even open their mouths wide enough to eat adult prey. Animals raised as livestock are typically slaughtered relatively young, he said, and farmers and breeders retain the most robust and fertile adults.

But commercial fishing nets and other gear that comply with conservation regulations typically trap large fish while letting smaller ones escape. Trophy hunters seek out the largest animals. And for some fish in some areas, as much as 50, 60 or even 80 percent of the stock may be caught every year.

“Targeting large, reproducing adults and taking so many of them in a population in a given year? that creates this ideal recipe for rapid trait change,”Dr.Darimont said.

Some fisheries scientists have said their studies of fish stock had not shown a correlation between fishing intensity and growth rates. And some wildlife conservationists question the idea that hunting can have harmful effects on species.