Factors affecting population growth

A population is a group of organisms of the same species living in an area. Its size increases when births exceed deaths and decreases when deaths exceed births. Factors that affect survival or reproduction therefore affect how quickly the population changes.

Food supply and competition

When food is plentiful, more organisms can survive and reproduce, supporting population growth. If food becomes scarce, fewer organisms may survive or reproduce, so growth slows or the population decreases.

Organisms compete when they need the same limited resources. As a population grows, more individuals may compete for the available food and other resources. Some may not obtain enough to survive or reproduce, reducing population growth.

Predation and disease

Predation occurs when one organism kills and eats another. If more members of a population are killed by predators, deaths increase. This can slow population growth or cause the population to decline.

Disease can also increase deaths in a population. If disease causes deaths to exceed births, the population decreases.

The combined effects of food supply, competition, predation and disease help determine the number of births and deaths, and therefore the rate and direction of change in population size.