Fact 1: Harming an animal species causes that animal 's population to decrease.

Fact 2: If mortality is greater, then the population decreases.

Given the two facts above, answer the question "what can cause a population decline?" with the following options: 
- wind
 - magma
 - bacteria
 - influenza
 - mortality
 - a pathogens
 - reproduction
 - parasites


 

     mortality    