Answer the following question given this paragraph: 

Population size is the number of individuals in a population. Population density is the average number of individuals per unit of area or volume. The pattern of spacing of individuals in a population may be affected by characteristics of a species or its environment.


Q: What is the average number of individuals per unit of area or volume called?

 Choices:

- crowdedness

- population structure

- population count

- population density

A:
population density
