Let's set the stage... in a class of 21 kindergarteners, there is a birthday party happening. However, the child (we will call him Bryan) only brings 20 cupcakes. In the best and most hilarious way that you can, describe what might occur at this birthday party.
Ok, now apply the same situation to a bunch of lions in a pride. There are 21 lions but only enough food for 20, what happens to the lions?
And again we are back in the kindergarten classroom, this time there are only 18 chairs for these 21 students. Describe once again in the funniest most creative way ever, what would happen.
Now apply this to a bunch of birds. There are 16 adult birds but only enough nests and materials for nests for 10 birds. What will happen?
We call this competition for resources, and it is part of what drives natural selection. If there is competition for resources there is pressure on animals to have the best traits and therefore natural selection occurs. What other resources might plants or animals fight over besides food and shelter?
Do you think this competition occurs in artificial selection?