An ecosystem is where plants and animals live with and interact with nonliving elements, both natural and human-made. Ecosystems host biotic or living organisms, as well as abiotic or nonliving parts. Biotic organisms include plants and wildlife, while abiotic components of an ecosystem include rocks, temperature, and soil. Ecosystems can be very big or very small; for example, a river is a huge ecosystem, and under a rock is a tiny ecosystem.

Every aspect of an ecosystem depends upon another, either directly or indirectly. To illustrate this, imagine the amount of rainfall in a given location is a variable (other variables include temperature, sunlight, and elevation) to predict the types of plants that will grow there. All of these factors will then support wildlife who depend on these plant species and weather conditions for survival.