Climate change may be throwing off the Kodiak bear’s eating equilibrium. Research says that, on years with warmer spring temperatures, elderberries ripen several weeks earlier than normal.
William Deacy, a postdoctoral researcher at Oregon State University, just published findings from a multi-year study of bears on the southwest side of Kodiak Island.
The paper looks at how climate change affects the relationships between two species that have evolved to rely on one another.
Deacy says elderberries are the Kodiak bear’s favorite snack, even more than salmon.
“The salmon is essentially the super Aktins diet for the bears. It’s just lean protein, almost no fat, and they end up gaining very little weight eating that, and the elderberries have a really perfect amount of protein for bears, and that allows them to gain weight really rapidly.”
Deacy says bears normally feed on salmon and then switch over to elderberries. This new pattern means that the elderberries are available at the same time as salmon spawn in tributary streams.
Deacy says the bears sense that and, once they switch over from one food source to the next, bears stick with the berries.
“It’s probably because they’re very, very good at detecting what foods are valuable to them, and they have instincts that tell them that these berries are the best food, and so they go and just eat those berries instead of having a mixed diet.”
Deacy says the warming temperatures force bears to choose between salmon and elderberries.
Meanwhile, the salmon spawn out and die. He says that leaves a gap where bears don’t have access to either elderberries or salmon. And partly due to how much energy bears expend while moving from point A to point B, they usually stick to one area with its own resources and salmon run patterns
Bears don’t appear to be suffering from these changes so far, says Deacy, and reproductive rates are about the same, if not better.
He says one possible effect of the timing change is that during early elderberry years, salmon may spawn more successfully.
“Just cause the bears aren’t there and the salmon can kind of do their thing without being killed, so that’s pretty intuitive, but we don’t know whether that would show up 4, 5, 6 years later as increase in returning salmon because there’s just so many other things that could happen to salmon in their life cycle before they come back.”
He says this study is one example of how climate change can scramble the timing of two closely tied species and disrupt a food web.