Ecology (noun)

1. The branch of biology that deals with the relations of organisms to one another and to their physical surroundings.
2. The relationship between living organisms and their environment.

Origin:

Late 19th century: from german ökologie, from greek oikos "house, household" + -logia (see -logy).

Examples:

1. He studied ecology in graduate school.
2. The ecology of the forest is fragile.
3. The ecology of the ocean is diverse.
4. He is an expert in the ecology of the desert.
5. The ecology of the mountain is harsh.