An ecological model uses to predict how the population of one species affects and is affected by the population size of another species or by it's interactions with some abiotic factor, like rainfall.

Biotic factor

Explanation:

Biotic factors are part of factors that determines the nature of the ecological system. They can either be living or dead organisms. Because they are considered to possess lives or had formerly existed, they are found in the biosphere and can reproduce.

Hence, to predict how the population of one species affects and is affected by the population size of another species or by its interactions with some abiotic factor, like rainfall. The ecological model uses a BIOTIC FACTOR.

This is because it is the interaction of the biotic and abiotic factors that determines the nature of the ecosystem.