Population density is the average number of individuals per unit of area or volume.
Economy is affected by population size and density.
Economy is affected by the average number of individuals per unit of area or volume.
What is affected by the average number of individuals per unit of area or volume?

[1] goats
[2] economy
[3] cows
[4] animals
[5] vegetation
[6] mammals
[7] bushes
[8] wind