by Dave Hanks
There is a very interesting triangle arrangement between the above three species. White-Bark Pine nuts are high in protein and fats. The nut’s make-up is about 74 percent of these two ingredients. Protein and fat is extremely important to both bears and squirrels. Of course, protein is important to all animals (humans included), but the fat is especially important for winter survival for species that hibernate or survive cold weather. Eskimos require much fat in their diet to prevent Fat Deficiency Syndrome (weakness, nausea, and blindness). Extreme cold necessitates a different diet than what we would think to be healthy.
Anyway, the Red Squirrel cuts down the pine nuts and stores them in giant middens (caches) – usually in softer ground at the base of a tree. These storage spots may contain as much as a three year supply of nuts for winter use. Then, enter the bear on the scene, especially Grizzlies. In the fall, the bear, which requires 24,000 calories a day most of the time, is in an increased feeding mode in preparation for winter torpor. They move up to the White-Bark Pine zone in search of nuts, a very rich and important food source for the bear. They can not climb trees to reach the nuts, however, the squirrel has solved that problem, and the bear simply has to dig the nuts out of the squirrel’s middens.
Trees can’t travel, but animals can and Grizzlies spread pine seeds in their scats – a benefit to the tree population. Squirrel populations do not become excessive because the Grizzly is a limiting factor on squirrel numbers when nut cycles peak. This is actually a benefit to the squirrel, because it keeps competition in check. When nuts are on the low end of their cycling, the bears are forced to eat more grass – which requires a daily intake of 90 pounds to meet their dietary needs.
I find symbiotic relationships most fascinating, and this triangular arrangement is no exception.