An ecosystem is a community of living organisms (biotic factors) that work in conjunction with nonliving things (abiotic factors) in the environment to survive. Biotic and abiotic factors in an ecosystem are interdependent, meaning they are linked together by biogeochemical cycles and by nutrient/energy flow. Ecosystems are dynamic and constantly changing. Each ecosystem has a variation of available resources to sustain life; they have a delicate balance of available resources that can support the biotic factors within the ecosystem. Each day, week, month, and year an ecosystem can experience variation with the biotic and abiotic factors.

Ecosystems are controlled by internal and external factors.

Internal Factor: natural processes that exist within the ecosystem (i.e. decomposition, root composition, environmental disturbances, ability of plants to photosynthesize for growth and food production, etc.)

External Factor: control resource inputs and are not influenced by the ecosystem itself (i.e. climate, parent material that makes the soil in the ecosystem, overall structure of the ecosystem, etc.)

Because these factors are constantly varying, the ecosystem is constantly responding with a feedback loop. From one year to another, ecosystems are exposed to variations within the environment causing change. For example: in resource-rich periods with ample food supply, it may create a dense animal population. Eventually, the food supply will become scarce because of overpopulation of animals and shortage of available resources (i.e. space, water); eventually the dense animal population will decrease naturally because of these changes. As part of the feedback loop, the ecosystem will always return to equilibrium or a balanced state unless altered by a greater factor. In example, humans exist and operate within ecosystems. However, their cumulative effects have the ability to alter ecosystems long-term.