Endangered polar bears are breeding with grizzly bears, creating “pizzly” bears, which is being driven by climate change, scientists say.
As the world warms and Arctic sea ice thins, starving polar bears are being forced ever further south, where they meet grizzlies, whose ranges are expanding northwards. And with that growing contact between the two come increasing hybrids (杂交种), “pizzly” bears.
With features that could give the hybrids an advantage in warming northern habitats, some scientists guess that they could be here to stay. “Usually, the hybrids,“pizzly” bears aren’t better suited to their environments than their parents, but these hybrids are able to search for a wider range of food sources, ” Larisa DeSantis, an associate professor of biological sciences at Vanderbilt University, told Live Science.
The rise of “pizzly” bears appears with polar bears’ decrease: their number is estimated to go down by more than 30% in the next 30 years. This sudden fall is related partly to “pizzly” bears taking up polar bears’ ranges, but also to polar bears’ highly specialized diets.
“Polar bears mainly consumed soft foods even during the Medieval Warm Period, a previous period of rapid warming,” DeSantis said, referring to fat meals such as seals. “Although all of these starving polar bears are trying to find alternative food sources like seabird eggs.” Actually, the calories they gain from these sources do not balance out(抵消) those they burn from searching for them. This could result in a habitat ready for the hybrids to move in and take over, leading to a loss in biodiversity if polar bears are replaced.
“We’re having massive impacts with climate change on species,” DeSantis said. “The polar bear is telling us how bad things are. In some sense, “pizzly” bears could be a sad but necessary compromise(妥协) given current warming trends.”
8. Why do polar bears move further south?
A.To create hybrids. | B.To expand territory. |
C.To deal with hunger. | D.To contact grizzlies. |
9. What makes “pizzly” bears adapt to natural surroundings better than their parents?
A.Wider habitats. | B.More food choices. |
C.Climate preference. | D.Improved breeding ability. |
10. What can we learn about polar bears from the passage?
A.Polar bears are increasing. | B.Polar bears like soft foods. |
C.Polar bears hate fat meals such as seals. | D.Climate change can benefit polar bears. |
11. What’s the main idea of the text?
A.Polar bears are changing diets for climate change. |
B.Polar bears have already adjusted to climate change. |
C.“Pizzly” bears are on the rise because of global warming. |
D.“Pizzly” bears have replaced polar bears for global warming. |