Inside of biomes, there can be trillions of living things. Those living things can be inside of completely different environments, even though the general climate is very similar. Think about the Cleveland area, for example. There are ponds, forests, cities, hills and even a lake! Areas within a biome like these can represent a different ecosystem because of the different materials available and the different living things that make up that particular area.
It’s not easy to say that one ecosystem starts at one place and ends at another. It is true that ecosystems influence other ecosystems, and biomes influence other biomes. In fact, scientists even like to talk about the “butterfly effect”: the way a butterfly flaps its wings here in North America could affect whether there’s rain in China! Since the entire world is connected, the best place to start with ecosystems is what is necessary to have an ecosystem.
Think about what you need in order to survive. Doctors say that you can survive 4 to 6 weeks without food and at most 10 days without water. It’s clear that all living things need food and water, in some form, even if food comes from the sun or water comes from the air. But what else do you really need?
Believe it or not, you need space. All living things require space, so that they can get their food and water, especially if they have to hunt down that food. The other surprising need of all living things is shelter of some sort. Many living things are capable of making their own shelter (like a snail has a shell or a human builds homes), but all living things have fragile parts that need to be protected from the environment.
Depending on how much food, water, space and shelter is available in the ecosystem, a certain amount of organisms will be able to survive in the ecosystem. The maximum number of a particular organism that can survive is called the carrying capacity of the ecosystem for that organism.
More importantly, a healthy ecosystem also recycles materials. This means that after a deer eats the leaves off a tree, the deer poop can then be decomposed by bacteria and worms into the soil, where plants use it for nutrients to make new leaves. This also means that a river carries water from the top of a mountain, and that water collects in a lake. The water from that lake evaporates into the atmosphere, falling as rain onto the mountain, where rivers take it back down into the lake.