How is natural selection related to niche?

First of all, I'm pretty sure this is a biology question, not a business question. Second, a niche is a certain, specified area. Let's take a school for an example. An entire school could be considered an ecosystem, but each classroom is it's own specialty, or niche. In each nice, there are going to be some students who are well prepared for the class, and some who are not. The ones that are well prepared with outlast those who are not and they will get better grades.