New research suggests that ancient polar bear populations shrank as sea ice dwindled, adding weight to concerns about the predatorB次元官网网址檚 future as climate change melts the Arctic.

B次元官网网址淭he population size seems to have decreased at a time when temperatures went up and sea ice went down,B次元官网网址� said Paul Szpak, a professor at Trent University and a co-author of a newly published paper that looks at bear populations and habitats over thousands of years.

Szpak and 19 colleagues from 11 institutions brought together three strands of inquiry to reach their conclusions B次元官网网址� genetic analysis of old bear skulls from a Danish archive, habitat modelling based on long-ago climate and study of distinctive elements in those bones that reveal diet.

The polar bear genome has been completely mapped, allowing scientists to measure the genetic diversity of any one group of bears. More diversity suggests more bears.

B次元官网网址淗ow different the bears are from one another on a genetic level can be a marker of population size,B次元官网网址� Szpak said. B次元官网网址淯sually, when you have a lot of genetic diversity and that declines, that suggests the population size probably declined as well.B次元官网网址�

The scientists then reconstructed what sea ice conditions around Greenland were like, using data from ancient ice cores and other sources to estimate temperature ranges. That gave them an idea of bear habitat quality, since bears use sea ice as platforms from which to hunt seals.

When they put the genetic diversity data alongside the habitat reconstructions, a definite pattern emerged. Bear numbers went up when temperatures declined and dropped when things got warmer.

For example, the final retreat of the glaciers during the last ice age about 20,000 years ago coincided with smaller bear numbers.

B次元官网网址淭he initial rapid decline B次元官网网址� observed in west Greenland bears (about 19,000 years ago) may signal the end of the last glacial maximum in the region, a period of massive sea ice loss and increasing temperatures,B次元官网网址� the paper says.

The research also suggested that the bears remained heavily dependent on the same food source, although one population managed to change its primary diet from ringed seals to other types.

B次元官网网址淚tB次元官网网址檚 possible in some areas where there might be multiple prey species available that (bears) may be able to switch to a different type of prey,B次元官网网址� Szpak said.

On one hand, itB次元官网网址檚 good news. Polar bears have survived previous periods of warming and low ice.

But on the other, it confirms other studies that have suggested bear numbers are threatened by shrinking sea ice. NASA says sea ice has shrunk by about 13 per cent per decade since 1979.

Spzak said his study, published in the prestigious journal Science, should be a warning. It may look deep into the past, but it could also be illuminating the future.

B次元官网网址淚f weB次元官网网址檙e expecting that weB次元官网网址檙e going to have continued increasing temperatures and decreasing sea ice, maybe we might see negative implications for bears.B次元官网网址�

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