Streams and trout are just a part of bigger natural systems called ecosystems. Ecosystems include everything living and nonliving in an area. All animals, plants, fungi, bacteria, rocks, soil, sunlight, water, air, energy and everything else in an area make up an ecosystem.
Everything in an ecosystem is connected to everything else. Looking at what eats what is one way to see how everything is connected. For example, the sunlight shines on trees near a stream, and that’s how trees get their energy. Then in the fall, most trees drop their leaves. Any leaves that fall into the stream become food for some insects that like to shred them up and eat them. Then, there are bigger insects that like to eat the leaf-shredders. Trout often hunt for these bigger insects and gobble them up to grow big and get energy to swim. Sometimes, raccoons, hawks, bear or people manage to catch the trout and eat them. We get energy from our food, such as those trout, and that makes us part of the ecosystem, too!