Answer
Organisms of different species can interact in many ways. They can compete, or they can be symbionts—long-term partners with a close association. Or, of course, they can do what we so often see in nature programs: one of them can eat the other chomp! That is, they can form one of the links in a food chain.
In ecology, a food chain is a series of organisms that eat one another so that energy and nutrients flow from one state to another.