An ecosystem is a community of organisms that interact with each other and with the abiotic and biotic factors in their environment. Abiotic factors are chemical and physical factors such as temperature, soil composition, and climate, along with the amount of sunlight, salinity, and pH. Biotic means living, and biotic factors are the other, living parts of the ecosystem with which an organism must interact. The biotic factors with which an organism interacts depend on whether it is a producer, a consumer, or a decomposer.
Producers are also known as autotrophs , or self-feeders. Producers manufacture the organic compounds that they use as sources of energy and nutrients. Most producers are green plants or algae that make organic compounds through photosynthesis . This process begins when sunlight is absorbed by chlorophyll and other pigments in the plant. The plants use energy from sunlight to combine carbon dioxide from the atmosphere with water from the soil to make carbohydrates, starches, and cellulose. This process converts the energy of sunlight into energy stored in chemical bonds with oxygen as a by-product. This stored energy is the direct or indirect source of energy for all organisms in the ecosystem.
A few producers, including specialized bacteria, can extract inorganic compounds from the environment and convert them to organic nutrients in the absence of sunlight. This process is called chemosynthesis . In some places on the floor of the deep ocean where sunlight can never reach, hydrothermal vents pour out boiling hot water suffused with hydrogen sulfide gas. Specialized bacteria use the heat to convert this mixture into the nutrients they need.
Only producers can make their own food. They also provide food for the consumers and decomposers. The producers are the source of the energy that drives the entire ecosystem. Organisms that get their energy by feeding on other organisms are called heterotrophs , or other-feeders.
Some consumers feed on living plants and animals. Others, called detrivores, get their energy from dead plant and animal matter, called detritus . The detrivores are further divided into detritus feeders and decomposers. The detritus feeders consume dead organisms and organic wastes directly. Decomposers break the complex organic compounds into simpler molecules, harvesting the energy in the process.
The survival of any individual organism in an ecosystem depends on how matter and energy flow through the system and through the body of the organism. Organisms survive through a combination of matter recycling and the one-way flow of energy through the system.
The biotic factors in an ecosystem are the other organisms that exist in that ecosystem. How they affect an individual organism depends on what type of organism it is. The other organisms (biotic factors) can include predators, parasites, prey, symbionts, or competitors.
A predator regards the organism as a source of energy and matter to be recycled. A parasite is a type of consumer organism. As a consumer, it does not make its own food. It gets its food (energy and matter to be recycled) from its host. The organism's prey is a source of energy and matter. A symbiont is a factor that does not provide energy to the organism, but somehow aids the organism in obtaining energy or matter from the ecosystem. Finally, a competitor reduces the organism's ability to harvest energy or matter to be recycled. The distribution and abundance of an organism will be affected by its interrelationships with the biotic environment.
Humans are one of the few organisms that can control how the other biotic factors affect them. Humans are omnivores, consuming both producers and other consumers. Humans can also adjust the length of the food chain as needed. For example, humans who must deal with shortages of food resources usually alter their eating habits to be closer to the energy source. This is sometimes called eating lower on the food chain. Since approximately 90 percent of the energy available at each level of the food chain is lost to the next higher level, shortening the food chain saves energy and uses food more efficiently.
Humans are also biotic factors in ecosystems. Other organisms are affected by human actions, often in adverse ways. We compete with some organisms for resources, prey on other organisms, and alter the environment of still others.
see also Ecosystem; Habitat.
Caldwell, Douglas E., James A. Brierley, and Corale L. Brierley, eds. Planetary Ecology. New York: Van Nostrand Reinhold, 1985.
Jordan, William R., III, Michael E. Gilpin, and John D. Aber, eds. Restoration Ecology: A Synthetic Approach to Ecological Research. New York: Cambridge University Press, 1988.
Krebs, Charles J. Ecological Methodology. Menlo Park, CA: Benjamin/Cummings, 1999.
Worster, Donald. Nature's Economy: A History of Ecological Ideas. New York: Cambridge University Press, 1994.
The food chain begins with producers, living things that take minerals and gasses from the environment for support. Consumers feed off of producers. Herbivores are plant-eating animals, while carnivores eat other animals. Onmivores are people and animals who eat both plants and other animals. The last link on the chain contains decomposers, who feed off dead plants and animals, reducing their remains to gasses and minerals.