Acknowledgement: The essence of the material in this issue is taken from Wikipedia at http://en.wikipedia.org/wiki/Ecosystem and reformatted, abbreviated and paraphrased to facilitate quick assimilation.

A system is a set of connected things or parts forming a complex whole.

For example, a system of transport would be a set of connected trucks, trains, roads, railroads, loading and offloading docks, and depots forming a complex whole.

The word Eco- concerns living things in relation to their environment. It derives from Greek oikos, household, house, or family.

An ecosystem is a community of living organisms (plants, animals and microbes) in conjunction with nonliving components (things like air, water and mineral soil), interacting as a system.

A coral reef is one example.

The tadpole pond is another example

Ecosystems can be of any size but usually encompass specific, limited spaces (although some scientists say that the entire planet is an ecosystem).

Abiotic is a thing that is physical rather than biological: it contains no life.
All matter is abiotic. Rocks, sand, volcanos, waterfalls and ponds are examples of abiotic environments.

Energy, water, nitrogen and soil minerals are essential abiotic components of an ecosystem.

The energy that flows through ecosystems is obtained primarily from the sun.

By feeding on plants and on one another, animals play an important role in the movement of matter and energy through the system.

Decomposers use dead organisms and non-living organic compounds as their food source.

Examples of decomposers are bacteria, fungi and worms.

Ecosystems in similar environments that are located in different parts of the world can have very different characteristics simply because they contain different species.

The introduction of non-native species can cause substantial shifts in ecosystem function.

Invasive bamboo is one example:

Although humans exist and operate within ecosystems, their cumulative effects are large enough to influence external factors like climate.

The need to consider long-term ecosystem health and its role in enabling human habitation and economic activity is urgent. 

And the elephant and oak are in our thoughts too.