In ecology, there are different levels of organization regarding the biotic, or living factors, in the ecosystem. An individual is a single organism, a population is a group of organisms of the same species in a particular area at the same time. In a species, members can only produce fertile offspring with other members of that species. If one considers all of the various populations that are found in a given area, that is known as a biological community. For example, all the organisms living on a dead tree can be considered a community. Various species of worms, insects, moles, moss, fungi, etc. will all reside there and carry out various niches. For example, fungi are saprophytes and will break down dead organic matter. Life within a pond can be a community. Various algae, pond weeds, insects, birds, crustaceans, fish, etc. reside and interact there. Finally, forest residents can be a community. These include populations of oak, maple, beech and pine trees along with birds, squirrels, deer, owls, bears, ferns, insects, fungi and wildflowers which all live and interact in this unique habitat.