Human Hunting Shapes Animal Populations

Jan. 13, 2009 -- Hunting by humans has such a lasting effect on animal populations that the appearance and behavior of some species are changing as a result, according to a new study.

The paper, published in this week's Proceedings of the National Academy of Sciences, is the first to compare the rate of such change among hunted species with changes that have occurred under natural conditions -- such as flood, disease or drought -- and changes due to other human-caused factors, such as pollution and habitat loss.

One explanation for the trait changes seen in hunted animals is that hunters often target prey of a particular age and size, removing them from the breeding population.

"Ironically, many hunting and fishing regulations encourage hunters and fishers to target the larger individuals," lead author Chris Darimont told Discovery News.

Related Content:

"For example, fish below a certain size often must be released back into the water, so some management prescriptions can actually create these novel evolutionary conditions that lead to the rapid trait changes we observed," added Darimont, a postdoctoral fellow in the Department of Environmental Studies at the University of California, Santa Cruz.

He and his colleagues analyzed 40 "human predator systems" comprising 29 species that included fish, hoofed animals, and even plants.

The researchers found that in 95 percent of cases, hunting by humans was the cause for decreases in body and horn size seen in many of the animals. In 97 percent of cases, hunting was also responsible for animals reproducing at earlier ages.

Darimont said Bighorn sheep of Alberta, Canada, are one prominent example, having seen a 20 percent reduction in body and horn size in 30 years. He also said that, due to fishing, "Atlantic cod of Canada's east coast have shifted the timing of their first reproduction from an average of six years to an average of five years in only 20 years."