Community and ecosystem interactions

Interacting groups of species are thought of as communities in which each kind of organism has a specific niche or role to play. Some organisms play minor roles while others play major roles, but all are part of the community. For example, the grasses of the prairie have a major role since, without them, there would be no prairie. Grasshoppers, prairie dogs, and bison are important consumers of grass. A meadowlark, though a colourful part of the prairie scene, has a relatively minor role that has little to do with maintaining a prairie community.
Communities consist of interacting species, but these species do not interact in vacuum. They must interact with the physical world around them as well. The physical world has a major impact on what kinds of plants and animals can live in an area. The kind of soil and the amount of moisture influence the kinds of organisms found in the area.
Organisms can also impact their physical surroundings. Trees break the force of the wind, grazing animals form paths, and earthworms create holes in the soil. This system of interacting organisms and their nonliving surroundings is frequently referred to as an ecosystem. While the concepts of community and ecosystem are closely related, an ecosystem is a broader concept because it involves the physical as well as the biological realm.
Major Roles of Organisms
Several categories of organisms are found in any ecosystem. Producers are able to make new, complex, organic material from the atoms in their environment. To do this, they must have a source of energy. In nearly all ecosystems, this energy is supplied by the sun, and the organisms that utilize this energy are plants that carry on photosynthesis. Since producers are the only organisms in an ecosystem that can trap energy and make new organic material from inorganic material, all other organisms rely on producers as a source of food, either directly or indirectly. These other organisms are called consumers because they consume organic matter to provide themselves with energy and the organic molecules necessary to build their own bodies. Primary consumers eat producers (plants) as a source of food. They are also known as herbivores. Secondary consumers or carnivores eat other animals. Some carnivores eat herbivores, while others may eat other carnivores. In addition, many animals, called omnivores, have mixed diets that include both plants and animals.
A final category of consumer is the decomposer. Decomposers use nonliving organic matter as a source of food. Many small animals, fungi, and bacteria fill this niche.