ecology, greek meaning house, study oh how organism interact in an environment. environmental supports systems: things on which humanity relies for fod, water and protection against natural catastrophes. some examples of these are: watersheds, agriculture lands, and wetlands. an ecological system may be an organism, a population, or assemblage of populations together, an ecosystem or the biosphere. each smaller system is a subset (part) of the next larger one. ultimately, all environments are linked together in a single biosphere [known as the ultimate ecological system] population: many organisms of the same kind living together. populations differ from organism because populations are potentially immortal; births replace deaths. they also have roper ties such as geographic ranges, densities, and variations in size or composition(evolutionary responses). community: populations of different kind make up an ecological community.