An animal species needs to have enough resources, like food and water, to survive in any given environment. However, because resources are limited, only a certain number of animals of a particular species are able to survive in a given habitat. The greatest number a habitat can support is known as the carrying capacity. If nothing happens to disrupt or unbalance the relationship between the animal and its habitat, the carrying capacity will remain stable. However, a carrying capacity is not fixed. If there is a significant disruption, such as an environmental event that alters the amount of available resources in the habitat, the carrying capacity will change
<-NARRATOR:-> Now listen to part of a lecture in a biology class.
<-MALE PROFESSOR:-> OK, so let's talk about what happened to a certain type of insect-
a moth, a red and black moth that lives in Europe.
These moths eat a plant called ragwort,
and they live in fields where the ragwort plants grow.
Now, there was a group of moths that lived in one of these fields...and for many years, there was a lot of ragwort growing there.
So the moths had plenty to eat,
and the total number of moths in the field stayed pretty much the same.
But then one year it rained a lot less than usual,
and the ragwort didn't grow as well.
The result was that the moths didn't get enough to eat, and many didn't survive...
but even the ones that did survive didn't lay as many eggs as before.
So that year the moth population in the field was quite a bit smaller.
The next year, though, the amount of rainfall returned to normal again.
Many more ragwort plants grew, and once again there was a lot available for the moths to eat.
So that year the moth population increased
and the female moths laid many more eggs than the year before.
And now, after all that rainfall and plant growth,
there were just as many moths in the ragwort field as there were before.
Explain the concept of carrying capacity, using the example of the moths and ragwort.