1.1.1ecosystems 1.1 Living Things and Their Environment 1.1.1 Ecosystem. An ecosystem is a group of living and nonliving things that interact with each other over time. Everything in an ecosystem affects everything else. For example, oak trees require sunlight, soil, and moisture to grow. When leaves fall from the trees, the organic material decomposes and enters the soil, thereby improving the soil's ability to hold water and nutrients.
Squirrels depend on oak trees for food and as places to build nests.
In turn, the squirrels help the oak tree to reproduce by burying acorns. The oak tree, the squirrel, and the soil all depend on one another. A bank vole feeds on an acorn.