Ecosystem Functions

Three levels of organisms regulate the flow of energy in ecosystems: the producers, the consumers, and the decomposers. They are organized in complex food webs. Autotrophy—plants, algae, and some bacteria—are the primary producers of an ecosystem. Heterotrophy—animals, fungi, most protests and bacteria, and a few non‐green plants—are the consumers in ecosystems. They obtain their energy and carbon from the organic material produced by the autotrophy. Four tropic (feeding) levels are recognized: The primary producers constitute the first level, followed by three levels of consumers. Primary consumers are the herbivores (plant eaters) that feed directly on the primary producers. The next level includes flesh‐eaters, the primary carnivores that consume the herbivores. The top or fourth level is that of the secondary carnivores that dine on the primary carnivores. At each level, some of the energy acquired is used to do the metabolic work of the consumer, some is stored within the substances of the consumer's body, and much is lost to the environment as heat (not really ?lost? since the heat maintains the temperature balance of the Earth and drives the wind circulation patterns that produce the climates).