The adaptability and interconnected nature of the organisms living in ecosystems helps to maintain the habitats in the natural world. For example, if one important species begins to disappear from a habitat, other species begin to fill the void. Conversely, if a species becomes too numerous, the plants and animals that it relates with adapt to the increased population.
Ecosystems are collections of large numbers of interconnected species, each of which has different needs. This broad diversity of needs ensures that there are enough producers, consumers and decomposers to keep the habitat functioning as it should. As small disturbances occur to the habitat, the relative number of individuals and species varies. Over time, these disturbances tend to disappear, returning the conditions to normal. When this occurs, the number of individuals and species returns to normal.
For example, if too many oak trees die in a forest, the number of squirrels living in the forest decreases. This means that there are fewer predators eating acorns, and so, after 20 or 30 years, the number of oak trees returns to its previous levels. Now, with more acorns present, the squirrel population rebounds as well.
While ecosystems often last a long time in the natural world, most evolve just as species do. In some areas, this process takes thousands of years, while other ecosystems may evolve and change over the course of a few years. For example, in the Eastern United States, barren fields usually evolve into pine-dominated forests over many years and eventually evolve into oak-hickory forests. Once at this stage, the ecosystem is referred to as a climax habitat, meaning that it remains in this form unless disturbed by a fire or other catastrophic event, according to Marietta College.