On the surface, an ecosystem refers to any area where living things interact with each other and the environment. You may hear of a forest ecosystem, an ocean ecosystem or a desert ecosystem, based on the predominant organisms, physical characteristics and climate of an area. Beyond this basic definition, however, any ecosystem consists of relationships. In an ecosystem, plants, animals, other living things and non-living elements form networks of mutual dependency. These networks provide food, shelter and the means of survival to the living inhabitants.
Living Organisms and Their Behaviors
Living things belong to the same ecosystem not because they live together, but because they form relationships with each other. They may depend on each other for food, protection, shelter or reproduction. These relationships form a complex web of interdependency. For example, a tree can provide food and a place to nest for birds. The birds, in turn, can spread the tree's seeds or pollen, helping the tree species to reproduce. The same birds may be hunted by other animal species, which benefit because the tree has helped their prey survive.
Non-Living Resources and the Physical Environment
Non-living elements are important resources in an ecosystem. Plants and animals rely on such factors for nutrients, water, shelter, and environmental cues that determine behavior. A pond, for instance, may provide drinking water to many species, shelter for fish, a breeding ground for insects and frogs, and yet be a hunting area for predators. In the same way, the change of the seasons to a colder climate may cause some species to migrate or hibernate.
Natural Cycles and Flows
Ecosystems can be described by the way in which energy -- often as nutrients -- and other physical elements flow through it. A food web, for example, shows how energy from the sun is converted into nutrients by plants, then consumed first by plant eaters, and then by meat eaters. The flow includes decomposers, such as worms and bacteria, that break down dead tissue and return nutrients to the soil. Other key flows describe how physical substances, such carbon and nitrogen, flow through an ecosystem for use as nutrients.
Stability of Ecosystems
A number of factors can indicate whether an ecosystem is likely to thrive. One of these is biodiversity, which describes the variety of life within an ecosystem. This can include the number of species and the genetic diversity within each species. Ecosystems with high levels of diversity are more likely to survive the extinction of one species. Another key factor is the availability of resources. Populations tend to grow until they are in balance with the available resources. If natural changes or human activity diminishes resources, an entire ecosystem could be at risk.
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