A creature does not have to consume the salmon directly to benefit from the oceans gift. The insects that colonize carcasses are devoured in turn by wasps, birds and other insect-eaters, including small mammals such as voles and mice that eat not only the insects but the carcasses themselves. We have found that densities of insect-eating songbirds can be higher along salmon streams than along waterways that do not support spawning salmon, suggesting that the bird communities respond to the abundance of insects produced by the harvest of salmon carcasses.
In the longer term, the feeding of all these animals, together with leaching by rain and microbial activity, breaks down the carcasses, making the nitrogen, phosphorus and other nutrients available to streamside plants. Plant growth in northern forests is often limited by either nitrogen or phosphorus, and thus the bears feeding activities may influence growth rates of many plant species in these areas. Not surprisingly, one study found that growth of Sitka spruce, the dominant streamside tree in the area, was three times greater along salmon streams than along nonsalmon streams. In several studies, researchers correlated the amount of salmon-derived nitrogen or carbon directly with the movements of bears, providing further evidence that their feeding behavior is the mechanism that delivers the salmon nutrients to riverside plants.
1. Why did fishery managers pay much attention to the hungry bears in the late 1940s in Alaska?
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