捕猎规则改变母熊的哺育方式

This is Scientific American - 60-Second Science. I'm Jason Goldman. In North America, many critters commonly encountered today-like wild turkeys or white-tailed deer-

were brought back from near oblivion through conservation efforts led by hunters. Meanwhile, in Africa, some of the most charismatic species are now being hunted into extinction.

But hunting can also have impacts that are far more subtle. Take the brown bear, known here in the U. S. as the grizzly.

When large mammals like grizzlies are hunted, evolution might select for speedier life cycles. That is, in order to successfully reproduce before they risk getting shot,

bears might begin having cubs at a younger age. That change also allows them to reproduce more times throughout their lives.

But that's not the only possible reaction to being hunted. The brown bear population in Sweden has been monitored for about 30 years.

And researchers in Scandinavia have noticed that females started to change their reproductive strategies. And they would observe that females would keep their cubs for longer periods of time nowadays.

University of Sherbrooke biologist Joanie Van de Walle. Usually females give birth in January while in their den. . .

But some females, rather than weaning their cubs after one year and a half, continue to care for them for an extra year. So some brown bear mothers in this population began to spend more time, not less, caring for their cubs.

And we have seen that since 2005 the proportion of females that keep their cubs for two years and a half has increased dramatically. Nowadays, its about 36 percent of females that use that tactic,