Ecology is the study of the interrelationships between an organism and its environment. Ecosystems have no specific size requirement. There is an ecosystem under your fingernail right now. The only requirement is that there are living things present.
Ecosystems, like organisms, are organized into increasingly more complex units. Just as cells make up tissues, tissues make up organs etc, organisms are part of larger groupings in an ecosystem. This is the way we refer to that organization:
Organism: A single living member or a species
Population: All of the members of a particular species living in an ecosystem
Community: All of the living things in an ecosystem (all the populations together)
Ecosystem: The community plus the non-living factors
The ecosystem an organism lives in is said to have two factors, non-living and living. Ecologists have named these factors abiotic and biotic respectively. The prefix a- stands for without, while the three letters bio- means life. Add the two meanings and we can come up with a definition of abiotic: non-living factors. Biotic factors can then be determined to be all the living factors that surround an organism within its environment. Be careful, most ecologists still refer to dead and decaying organisms as biotic because their nutrients can still be used as food in the food chain.
The abiotic factors of an ecosystem (temperature, precipitation, fresh water, soil, terrain) determine what biotic factors can exist in that area. Most importantly, the amount and kinds of plants are determined by the abiotic factors. Then other organisms can also be present that depend on those plants.
