Factors affecting population
- (a) Natality : Birth rate.
- (b) Mortality : Death rate.
- (c) Population growth : Shows two types of curve :
 S. shaped curve.
 J. shaped curve.
- (d) Emigration : Permanent outward movement. Decreases population.
- (e) Immigration : Permanent inward movement. Increases population.
- (f) Migration : Two way movement of entire population. Does not change the size of population.
- (g) Biotic factors : Growth rate of certain population decreases with the increase in density (density dependent) before the carrying capacity of the environment is reached, predators also keep the size of a population under check.
- (h) Carrying capacity : of an environment is the maximum number of individuals of a population which can be provided with all the necessary resources for their healthy living.
(i) Biotic potential : Maximum capacity of a population to reproduce under ideal conditions (environmental).
(ii) Control of population : It is by three factors :
(a) Geographic factors
(b) Demographic factors
(c) Socioeconomic factors.

Community : An association of a number of different interrelated populations belonging to different species in a common environment, which can survive in nature, is known as biotic community (e.g. different species of organisms occurring in a pond constitute the pond community. The members of a community have different type of inter relationship.