<-NARRATOR:-> Listen to part of a lecture in an environmental science class.
<-FEMALE PROFESSOR:-> Roads-paved roads-are everywhere and sometimes seem like part of the natural landscape.
But of course, roads are not part of nature and, in fact,
road construction can have harmful effects on the environment
and seriously impact both animal life and plant life.
One harmful environmental effect of roads
is that they contribute to the movement of plant species from one area to another.
This causes problems for existing plants, plants already growing in that area...
because when a new plant species gets introduced into an area where it wasn't growing before,
the new plants compete for resources with the existing plant life.
For example, this happened in California with a weed called the yellow starthistle.
What happened was, the starthistle's seeds got stuck to the tires of cars driving down the road,
and the seeds were distributed to new areas.
This put the starthistle in competition for natural resources-like water-
with the original plant life of the area.
That made it harder for the native plants to survive.
especially major highways,
can act as barriers
and divide up an animal's habitat into smaller ones where there's not enough food to support the population.
These busy highways,
with cars speeding past day and night,
act like boundaries that animals are afraid to cross,
so they sometimes get shut in on a small piece of land
where there isn't enough food to support them.
This is a serious problem for animals that need access to large expanses of land to look for food.
For example, there are these foxes,
called kit foxes,
that live in the southwestern United States.
They hunt small animals like mice and squirrels,
which are spread out over large areas of open grasslands.
And now, because of these roads,
the kit fox population has declined significantly...
because now they don't get enough food.
Using the examples of the starthistle and the kit fox, describe two ways roads can affect the environment.