An ecosystem is defined as living things (communities) and nonliving things that interact in an area. All energy in an ecosystem ultimately comes from the sun. Ecosystems differ based on factors like the amount of water, sunlight, and type of soil. Every community contains three member types: producers, consumers, and decomposers. Ecosystems can change due to natural causes like drought, disease, fire, or overpopulation, or due to human causes such as water pollution, air pollution, land pollution, or construction. Humans can help prevent ecosystem changes by using resources wisely, enacting pollution control laws, cleaning up litter, and keeping waterways clean.