An example of evolution
Let us say for instance,a beaver moves into a stream and dams it up.
This has taken place right here where I live.One dam has enough water backed up to flood a small town,if that town was below the beaver dam.It stretchs for over a 1/2 mile and in some places 50 feet across.
In one of man's attempts to improve upon nature,he has introduced Beavers into watersheds where they are incompatible with the flora and fauna.Beavers naturally subsist on soft woods such as cottonwood,aspen and willows.The beavers appetite quickly outstrips the growing ability of the native softwoods.
Fish fry are trapped and unable to reach their nursery.The trout downstream are unable to breach the dam to reach their spawning areas. Summer drought and winter freezes often kill fish trapped by the dam being there.
With the streamside trees being harvested for food and dam material,the banks begin to erode and the stream becomes silted in,thus the eggs will not produce because of oxygen difficiancy.Also water temperatures rise and kill the fish from lack of shade.
After this beaver has eaten all the soft woods he moves to another location to begin this cycle over.Now the first dam is unattended and washes out with the spring floods,carring all the silt which ruins the lower stream and it's habitat.All that remains is a dead stand of trees and a depleated fishery.
We are encountering many problems as this through the U.S.Government building dams to harness electric power.In a move to harness energy,the federal government is subsidizing the cost of our fisheries for hydro-electric power.
This epidemic is spreading throughout western watersheds.Damming streams can create long term damage to fisheries.Just check the damage done on the Columbia River to the salmon trying to reach their spawning grounds.
The fish migration routes become blocked,abrupt flow changes kill aquatic life,a food source for trout and salmon.This is a long list of environmental concerns.
One small dam on one small creek is harmless to the eco-system,but many small dams will be devastating to all life forms.
Unfortunately one dam is only approved at a time and the ruling is in favor of the builder.