Individual organisms belong to a population, all the members of a species within a particular area. The combination of all the different populations in the same area make up a community, in which organisms interact among themselves and with the physical environment to ultimately form an ecosystem.The place where a community lives, the abiotic components surrounding a community, are called the habitat.An ecosystem, a self-sustaining collection of organisms and their physical environment, is the sum of the community and the habitat.Ecosystems are characterized by chemical cycling and energy flow, both of which begin with the capture of energy from the sun by organisms called autotrophs. Other organisms called heterotrophs obtain their energy by consuming plants or other animals.Energy flows from the sun through plants and other members of the food chain as one species feeds on another. With each transfer, most energy is lost as heat. Thus, ecosystems could not stay in existence without a constant input of solar energy.