Rivers as Resources
The way we humans make use of our rivers cannot be separated from discussions about ecology. We are, after all, part of the river ecosystem. In fact, our influence on the river ecosystem is much greater than that of any of what we call keystone species.
Keystone predators have so much influence on a system that their removal, or their addition, to an ecosystem can completely change the make-up of that system. An example of a keystone species is the seastar, Pisaster ochraceous. R. T. Paine, then a professor at the University of Washington in Seattle, Washington, studied a rocky seashore community in the early 1960's and developed the concept of keystone species from what he observed. When he removed P. ochraceous from its seashore habitat, the mussel Mytilus californianus was able to dominate the intertidal community, and exclude most of the other usual intertidal species of animal from that site. In other words, the mussel would completely take over, by denying any other species a place to attach themselves to the rocks. The presence of the sea star ensured a vital, diverse seashore community because the sea star preyed on the mussel and kept its numbers down. |
As powerful an influence as a keystone species has, or a volcano or an earthquake or a tidal wave has, human influence on rivers can be far more dramatic. As a case in point, the Columbia River in Washington State is dammed from one end to the other: it was changed from a wild, tumbling river of many changes to a constant, steady series of lakes. The habitat was so altered that salmon have little chance of reproducing successfully, surviving in its waters, or making it back to the ocean. As a consequence, most salmon species utilizing the Columbia are now endangered. Contrast this to the late 1800's, when white people first started fishing the river: anyone could pull out so many salmon that it would be a major effort to get them home. Steelhead...