Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Polar bears (Ursus maritimus) depend on sea ice in the Arctic to hunt seals, rest, and raise their young. Sea ice is their platform for finding food: they wait by breathing holes in the ice to ambush seals when they surface. As the Arctic warms, however, sea ice forms later in the fall and melts earlier in the spring. Each decade since the late 1970s, the Arctic has lost about 13% of its summer sea ice extent.
With less ice, bears must swim longer distances or move onto land, where food is scarce. Studies from the U.S. Geological Survey show that in regions like Hudson Bay, Canada, the ice-free period has lengthened by about 3–4 weeks since 1980. As a result, bears spend more time fasting and their body condition has declined.
Data also show clear differences in survival and reproduction:
Adult bears in stable ice areas maintain normal weight and survival.
Bears in moderate ice-loss areas show reduced cub survival (about 75% → 55%).
In severe ice-loss regions, cub survival drops below 30%, and adult females often fail to reproduce.
Other Arctic species show contrasting outcomes. Some seals have adapted by shifting breeding grounds northward, while others that rely on thick ice (like the ringed seal) are declining. These differences demonstrate that in a changing habitat, some species can survive well, others less well, and some not at all.
The polar bear’s dependence on sea ice provides clear, measurable evidence of how survival depends on habitat stability - and how rapid environmental change can reshape entire ecosystems.
Year | Average Summer Sea Ice Extent (million km | Average Ice-Free Period (days) | Cub Survival Rate (%) |
|---|---|---|---|
1980 | 7.5 | 60 | 75 |
1990 | 6.8 | 75 | 68 |
2000 | 6 | 90 | 55 |
2010 | 5.1 | 110 | 40 |
2020 | 4 | 130 | 28 |
Make a claim, provide the evidence, and explain your reasoning for the statement:
“Polar bears survive well in stable sea ice conditions, less well when ice-free periods increase, and not at all when summer sea ice disappears.”
Claim:
Evidence:
Reasoning:
Refer to Table 1 in the Polar Bears and Sea Ice Decline resource.
Describe how changes in sea ice extent and ice-free periods affect cub survival over time.
Why are polar bears finding it harder to survive as Arctic ice declines?
What do changes in Arctic sea ice tell scientists about the climate?
Describe one possible solution scientists or communities could use to help polar bears survive as their habitat changes.