Question

when real world populations of plants and animals are analyzed why do they most often have the logistic growth curve

Answer 1

wrong

Answer 2

I've attached a graph of what logistic growth curve would look like.

Firstly, the difference between logistic and exponential growth curves are based on limitation. Exponential growth has seemingly no limitation placed upon it, so the rate at which the population grows increases. Logistic growth curves within population dynamics assert that there is some sort of limiting factor on the population. Often this is thought of in terms of resources, whether that is food, water, shelter, etc. **However, this could simply be any other density dependent control factor, such as disease or predation.**

With that limitation being in place, the population curve will look much like the exponential curve in the beginning: the rate at which the population grows will increase, forming a climbing line on the graph. However, as more and more individuals are born into the population, the population begins to be stressed by the limitations...now they have to compete for the set number of resources. As this happens, the rate at which the population grows begins to slow down, eventually stopping altogether and plateauing.

That all being said, the actual graph is much neater that what actually happens in the wild. There will be overshots and falls, but ultimately the population settles at the plateau. This point is called the carrying capacity...the population level that the given environment can support with some amount of stability.