An evolution question

My teacher told me to write a one page summary on,

species adaptation and how it relates to population change.
Im a little stumped.
Help?
Thank you ;)!

Population can change depending on natural selection, which species must adapt to. Here are three different types of adaptation:
Coevolution- organisms helping each other (bee and flower)
Convergent evolution- the same biological trait in two different organisms (frogs and ducks)
Adaptive radiation- one population dividing into smaller similar ones (finches)

Your teacher may be looking for the adaptive radiation one.... here is an example:
A population of salamanders of medium skin thickness is divided into two when a new mountain range forms. On one side of the mountain, the salamanders evolve thick skin. On the other, the skin of the salamander evolves to be thin. The two salamanders eventually become different species.
Hope this is what you are looking for :)