Which out of the four basic processes that act on the population growth contribute to an increase in population density ?

The population density in a given habitat during a given period fluctuates due to changes in four basic processes:

Natality refers to the number of births during a given period in the population that are added to the initial density.

Mortality is the number of deaths in the population during a given period.

Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.

Emigration is the number of individuals of the population who left the habitat and went elsewhere during the time period under consideration.

Therefore, Natality and Immigration contribute to an increase in population density, while Mortality and Emigration contribute to a decrease.

Answer: Natality and Immigration