Hunters Speeding Up Evolution of Trophy Prey?

January 12, 2009

Human hunters are pushing their prey to evolve faster than they would naturally, resulting in smaller and younger individuals over time, according to a new study.

Hunters' desire for the largest individuals—the "trophies"—influences plant and animal populations faster than natural selection and even other human impacts, such as pollution and habitat destruction.

Such preferences leave a disproportionate number of smaller animals and plants to reproduce.

The phenomenon of human-forced evolution is already known, said study lead author Chris Darimont.

But what's jarring about the new research is the rate at which whole populations are changing.

(Related: "Trophy Hunting May Push Polar Bears to 'Tipping Point'" [November 21, 2007].)

"Human-harvested organisms are the fastest-changing organisms yet observed in the wild," said Darimont, an evolutionary biologist at the University of California, Santa Cruz, whose work was also supported by the University of Victoria in Canada.

A classic example of natural selection is Darwin's finches on the Galápagos Islands, which rapidly evolve different beak styles to exploit varying food sources in periodic droughts. Organisms can also adapt in response to hardship, such as pollution or weather shifts.

Fast and Furious

Darimont and colleagues examined previously documented, hunting-induced changes across 29 species in 40 locations, including commercially targeted fish, bighorn sheep, caribou, and several marine animals such as limpets and snails. Two plant species were also included in the analysis: Himalayan snow lotus and American ginseng.

The researchers compared shifts in those populations with those in 20 species that face only "natural" pressures, such as climate, competition for resources, or animal predators.

The team also compared 25 species that are not hunted by people but that face other human-caused selection pressures.

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