Ecology is the study of the interactions among plants and animals and the physical environment .
Every population affects and is affected by other populations and by the physical environment in which they live. Conditions there control the survival and affect the success of all organisms. Nothing can exist by itself. Ecological relationships are the ways that things in an environment interact with each other. There is no way to study all the ecological relationships of the entire world, or even a single island, so we select small parts of the environment and specific relationships to study.