There are three major types of interactions among organisms: competition, predation, and symbiosis.
Competition: The struggle between organisms to survive in a habitat with limited resources.
Predation: An interaction in which one organism kills and eats another.
Predator: The organism that does the killing.
Prey: The organism that is killed.
Symbiosis: A close relationship between two species that benefits at least one of the species.
Interaction Among Living Things Slideshare