Life of a River - Biology
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
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.