Fact 1: Population density is the average number of individuals per unit of area or volume.

Fact 2: Population densities affect the balance of the environment.

Given the two facts above, answer the question "The average number of individuals per unit of area affect the balance of ." with the following options: 
- gravity
 - the environment
 - energy
 - Earth orbiting the Sun
 - an organism's body
 - objects that have mass
 - competition
 - power


 

  the environment       