Polar bears face ‘tipping point’
Climate change will trigger a dramatic and sudden decline in the number of polar bears, a new study has concluded. The research is the first to directly model how changing climate will affect polar bear reproduction and survival. Based on what is known of polar bear physiology, behaviour and ecology, it predicts pregnancy rates will fall and fewer bears will survive fasting during longer ice-free seasons. These changes will happen suddenly as bears pass a ‘tipping point’. Details of the research are published in the journal Biological Conservation. … “Some populations are expected to go extinct with climate warming, while others are expected to persist, albeit at a reduced population size,” says Dr Peter Molnar of the University of Alberta, Edmonton, Canada. … Southern populations of polar bears fast in summer, forced ashore as the sea ice melts. As these ice-free seasons lengthen, fewer bears are expected to have enough fat and protein stores to survive the fast. By developing a physiological model that estimates how fast a bear uses up its fat and protein stores, the researchers could estimate how long it takes a bear to die of starvation. “In both cases, the expected changes in reproduction and survival were non-linear,” explains Dr Molnar. “That is, as the climate warms, we may not see any substantial effect on polar bear reproduction and survival for a while, up until some threshold is passed, at which point reproduction and survival will decline dramatically and very rapidly.” …
