【推荐1】Polar bears normally need sea ice to hunt seals, but an isolated (孤立的) group of polar bears living on the mountainous coast of southeast Greenland have figured out how to make a living, even though the sea ice there melts away early in the year.

These bears have found a way to supplement (补充) their limited sea ice supply by hunting on freshwater ice that comes from glaciers on land. The glacial ice falls off in pieces into fjords (峡湾), where the pieces get together into a floating platform that the polar bears use to catch seals, according to a report in the journal Science.

Climate change is making sea ice less and less. “Loss of sea ice is the primary threat to polar bears,” says Kristin Laidre of the University of Washington, lead author of the new study. But, she says, this new work suggests some bears might be able to deal with a decreased amount of sea ice - at least for a while - in places like Greenland where they can take advantage of floating glacier ice.

While local people have long known that bears live in southeast Greenland, it’s a remote, challenging environment that’s not frequented by humans. “It’s a coastline with huge mountain peaks, lots of winds, extreme conditions and plenty of fogs.” says Laidre, who has spent years working with colleagues to survey polar bears living on Greenland’s 1,800-mile-long east coast.

To see what they could find in southeast Greenland, the team had to take helicopters from the nearest settlement and fly for two hours in a straight line to the coast. “We arrived in these fjords, very isolated fjords, and there’s essentially no sea ice or very poor sea ice offshore,” says Laidre, explaining that the researchers expected to find few bears. “But there were a lot of bears in these fjords,” she says. “It was clearly just a unique habitat.”

The sea ice continues to exist in these fjords for only around a hundred days a year, she notes, meaning that bears don’t have much time to use it as a hunting ground.

【推荐3】A new study, published in Science Advances, says there is a definite limit to human endurance (耐力), beyond which our bodies begin to break down.

The study indicates that the length of time that highly-trained athletes can sustain themselves might be relevant to the length of the endurance event and how many calories someone can burn.

To find the limit of the time, a US research team tracked extreme marathoners, mountain hikers and professional bicycle racers over a five-month period, measuring competitors’ basal metabolic rates ( BMR,基础新陈代谢率) — the amount of energy they consume when they rest. Then they looked at how many calories these athletes burned per day and finally concluded that the maximum amount of energy a human can consume is 2.5 times of his BMR.

But people can’t keep using this amount of calories all the time. “You can do really intense stuff for a couple of days, but if you want to last longer then you have to dial back,” the leader of the team, Herman Pontzer, an evolutionary anthropologist (人类学家) said.

He explained that the problem is our guts (消化道). “There’s a limit to how many calories our guts can effectively absorb per day,” he said. At that point, the body is burning calories more quickly than it can absorb food and turn it into energy.

These findings could help athletes to best work underneath this ceiling. For example, they could manage their daily exercise time based on their own BMR, to get enough calories and keep going.

However, Pontzer’s team can’t rule out the possibility of someone breaking this limit. “So I guess it’s a challenge to elite (精英) endurance athletes,” said Pontzer. “Science works when you’re proven wrong. Maybe someone will break through that ceiling some day and show us what we’re missing.”