All living things have four basic needs in order to survive: food, water, shelter, and space. An ecosystem consists of both biotic things, such as plants and animals, and abiotic things, such as rocks, water, air, and sunlight. A healthy ecosystem needs a good balance of these living and non-living things in order to create strong food chains. A food chain is a flow of energy from one organism to another or “who eats who” in an ecosystem.