Experimental manipulations of these systems are expensive and labor intensive. Let's talk about the ecology of populations .
Populations have a number of characteristics that are of interest to ecologists.
Like distribution, density is influenced by biotic and abiotic factors in the environment. There are four primary factors that determine population size. We will ignore immigration and emigration and concentrate on natality and mortality. The difference between b and d determines whether the population increases, decreases or remains constant in size. Recall that mortality and natality underlie a population's ability to change in size.