Life of a River - Biology
Relationships

Plant and animal communities have coevolved with the flow, shape, connections and quality of the river systems in which they live. Just as animals are influenced by streams, streams may also be influenced by animals. One example is beaver, which can transform a small brook to a series of broad ponds and denude the banks of aspen. The effect on other wildlife is mixed. The ponds, for example, provide greater depth for fish such as brook trout. The ponds also support higher diversity of some insects, such as dragonflies, than the stream habitat might contain.

On the other hand, ponding and elimination of shade-giving trees cause the stream to grow warmer, to the detriment of trout. Over time, as beaver remove most of the suitable streamside trees and shrubs, they abandon their home, allowing the ponds to convert to a mudflat, meadow, and eventually, a forest.

But the most influential animal that impacts streams is the mammal Homo sapien sapiens. Humans are changing the flow, shape, connections, and water quality of most river systems, putting many plant and animal communities at great risk, and ultimately, us.