When does the exponential growth of a population start to slow down?

Exponential growth of a population start to slow down when there is a competition for resources.

An environmental niche plays a big role in the population decline rate. We must think of an environmental niche as a profession for organisms (what it does for the environment, how it responds, how resources are used, etc.) when a niche is occupied by multiple species competition amongst them occur.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.