How can the environment favor a particular trait in an organism?

Biotic factors can influence ecosystems, since they cause major changes in the environment by activities originated by living organisms. Deforestation, for example, reduces food and habitat for all organisms that make up an ecosystem, being a biotic factor with a high impact on ecological balance. In the same way, the outbreak of some disease that affects an entire population can unbalance the trophic relations, causing a collapse in the ecosystem.

The intra and interspecific relationships are also considered biotic factors that act in the functioning of an ecosystem, since it is through these relationships that the ecological balance is maintained. Predation, for example, keeps the population of primary consumers stable, preventing overexploitation of resources. Other relations commonly established between organisms are mutualism (mandatory association for the life of both species), competition (which may be for food resources, sexual partners or territory) and parasitism (a parasite survives by consuming its host, and may even kill him).