Bears Choose Berries

As weather patterns and seasonal temperatures continue to shift, scientists are constantly finding new ways in which the ecosystem around us is straining like cables on a listing ship. Fresh research conducted in part by Oregon State University faculty has found that warming temperatures on Kodiak Island are altering the feeding schedule of Kodiak Brown Bears – a fine tuned balance of salmon and elder berries.

One way that changing climate patterns affect the ecosystem is by disrupting the seasonal timing of biological events. These disruptions impact plants and animals individually, but also in how and when they interact with each other as well.

For example, under typical conditions sockeye salmon begin making their spawning run up the tributaries of Kodiak Island early in June. During this time, the local brown bears eat 25 to 75 percent of the salmon, depositing their remains around the island as they go. Later in the season, around August and September, the red elder berries begin producing and the bears feed heavily on those.

What researchers found was that during unusually warm conditions, red elder berries ripen much faster, which means berry production then coincides with the salmon run. Interestingly enough, the bears shift their full attention to the berries, leaving the salmon to spawn in peace.

On one hand, the study found that the synchronizing of the food sources affected more than the three species involved. While the salmon spawned in much greater numbers, their bodies usually fertilize the island as the bears spread them around. The bears themselves gain weight much faster off of a diet lower in protein and higher in sugars.

On the other hand, the study deepened our understanding of how changing climate patterns affect different species. Much of our current understanding of climate-impacted food webs comes from studies on specialist species – species whose lives are directly connected to a very specific variable, be it a food source or seasonal trigger. This study focused on the brown bear, a generalist species whose food sources are not in peril, but become synchronized in time.

How will an increased salmon population influence their food sources? Will getting fatter earlier in the year hinder the bears? Each study like this illustrates again and again the fragile relationships that have developed in the natural world over millions of years. They are delicate connections that work subtly, but once the function is disrupted, it can have magnified effects that cascade down through the ecosystem’s many levels.

By Anthony Vitale