All living things must remain in balance, or equilibrium, also known as homeostasis. Our bodies maintain a balance of many things such as temperature. If we are too hot we sweat and if we are too cold we shiver. Our temperature must remain in equilibrium.
Even larger collections of living things like ecosystems must be in balance too. An ecosystem is a collection of living and non-living things in an area. There are lots of types of ecosystems we already know, such as a forest or a meadow. Any collection of living and non-living things in an area is an ecosystem, even a small ecosystem like your backyard.
Resources are plenty and predator and prey relationships are healthy. No competition for resources.