Explain the Ecosystems?
The ecosystem is yet another level, or ecological unit, studied by ecologists. An ecosystem encompasses all of the organisms (all the populations-the entire community) and includes the physical environment-the atmosphere, water, and soil. Studying ecosystem dynamics requires a holistic approach to the ecological unit.
The physical limits, or boundaries, of an ecosystem are not always distinct, since ecosystems usually grade into each other. Normally, units such as a tropical rainforest, a lake, or an estuarine salt marsh would be considered ecosystems. An estuarine salt marsh, for instance, is influenced both by the ocean and its associated communities, and by a river and its associated communities. The physical factors in a salt marsh ecosystem are in a constant state of flux. However, one can also speak of a terrarium or aquarium as being a separate ecosystem; even the entire globe can be thought of as a "global ecosystem."
Ecosystems are dynamic. They change over time. For example, if a volcanic island were newly formed out in the ocean, you would think the lava would probably not be the most hospitable place for life. Yet, some organisms will arrive by random means - flotsam on ocean currents, wind, seabirds, sea turtles, or marine mammals - and grab a foothold and survive. Lichens would be the most likely pioneers. Since they absorb moisture and minerals from the air, they would be able to live in barren conditions like those on the new island. They might produce chemicals that slowly break down the minerals, freeing up small amounts from the substrate at first. Ultimately they would die and decompose, providing a moist and nutrient-rich seedbed for other types of organisms. Each succeeding wave of organisms would alter the conditions slightly, allowing others to follow in time. This process is known as ecological succession.
Another example of ecological succession is the way in which, over long periods of time, ponds can be filled in and covered over with a forest ecosystem.