Fact 1: Harming an animal species has a negative impact on the population size of that species.

Fact 2: Pollution is usually harmful to one or more species of animal or plant.

Given the two facts above, answer the question "What is usually harmful to the population size of a species?" with the following options: 
- Pollution
 - reproduction
 - viruses
 - disease
 - habitat
 - ecosystems
 - influenza
 - deforestation


 

 Pollution        