The five levels of ecological organization are species, population, community, ecosystem and biosphere. Ecosystems may be studied on small local levels or at the macrolevel. Similarly, species, populations and communities may be examined individually or as larger groups as well.
The smallest branch of ecology is that of species. This group includes plants, animals and other living organisms that are biologically related and often bear some degree of physical resemblance. Species include animals and plants that live around the world and survive in water and on land. Monkeys, apes and ants are all examples of species, as are seaweed, ferns and sea urchins. At this level, individuals are not considered the same species if members cannot produce like offspring that may in turn reproduce to create the same species. Species are classified using a taxonomical structure; they are scientifically identified by two names, and the species name forms the latter word.
Populations are the second level of the ecological hierarchy. These structures are groups of organisms that belong to the same species and live and interact with other species members. Communities refer to location rather than organism type. Communities include groups (populations) of different organisms inhabiting a location. Forests, for instance, contain a community consisting of birds, plants, bacteria and trees.
Ecosystems are the next-highest level of classification. Ecosystems include all living organisms in an area and the nonliving factors of those places too. Finally, biospheres are parts of the planet that contain living organisms. Most of the world is considered a biosphere, including oceans and the atmosphere.