humans establish cities, they disturb habitats and destroy others.
But at the same time, they import new species of plants and animals
and create habitats for other unintended species.
can take place in many ways. Natural ground cover is replaced with
grasses and decorative plants, with native plants sometimes allowed
to remain. With non-native grasses and decorative plants, fertilizers
are used to provide essential nutrients that are not found natively,
theses spread across lawns, and find their way into river channels
where it promotes the growth of more plants at the expense of aquatic
species. Additionaly, waste dumped into streams lowers oxygen levels
during its decay and causes the death of plants and animals. Sometimes,
urbanization promotes the growth of native species populations,
such as squirrels and raccoons, and population size increases far
above the natural equilibrium.
Waterfowel, such as these ducks, have adapted to
urbnaization around Boulder Creek
River diversions help to prevent flooding around underpasses,
but disturb movement of fish poplutions and other aquatic species.