noun /ɪ.ˈkɒlə.dʒɪ,i.ˈkɑ.lə.dʒi/
The branch of biology dealing with the relationships of organisms with their environment and with each other.
As a graduate student, he was working on a thesis: The Ecology of the Black Creek Area. He had to investigate the relationships, past and present, of men and plants and animals in this region.
Wikipedia foundation.