When does the overlap of ecological niches occur? What does this matter for the biocenosis?

The water content in the human body is not constant and depends on many factors. Normal human physiology gives the following numbers:
the average water content in the body with a normal body fat is 65%;
in very thin persons, it can reach up to 70%;
in obese people, the water content in the body is the lowest and can drop to 55% and below, so that the normal water content in the body of a healthy person, without any disturbances and deviations, can be considered the figure of 65%.
Human blood is 78-82% water. And in newborns, numbers close to 80% can be observed.