What are biotic and abiotic factors?

Biotic and abiotic factors are the features of ecosystems, or geographic areas of a planet. Biotic factors are all living organisms, including microorganisms, plants, animals, and humans. Abiotic factors are all nonliving things, ranging from landforms to chemicals to climatic features. Biotic and abiotic factors are interrelated, meaning they work together, and they are involved in various natural cycles that keep ecosystems sustained and balanced.

Ecosystems

Ecosystems consist of geographic areas and all the interrelated things contained within them. These areas may have vastly differing sizes, from the tiny ecosystem of microorganisms in a drop of water to the massive ecosystem of an entire planet. Both land- and water-based ecosystems generally feature a wide array of features and factors, including those that are living (biotic) and nonliving (abiotic).

Biotic Factors

The word biotic comes from Greek words meaning "with life." Simply put, biotic factors in an ecosystem are all the living organisms in that system. For example, if the ecosystem was a house, the biotic factors would include the people who live in the house and any pets or houseplants they may own. In nature, biotic factors generally include macroflora (large plants), macrofauna (large animals and humans), and microorganisms in the soil, air, or water. These living organisms play important and interrelated roles in their ecosystems.

The three major roles for living organisms in the environment are producer, consumer, and decomposer. Producers are plants that use the power of the Sun and other natural forces to grow. Consumers are organisms that eat producers and other living organisms.
Decomposers
are organisms that break down dead things and waste materials to return their nutrients to the earth. Each role is important to the natural cycles that sustain an ecosystem. For example, a tree might grow apples, which a deer eats. Later, wolves may kill the deer for food. The remains of the deer then decompose, and their nutrients reenter the soil. Those nutrients may then help another apple tree to grow in that spot, thus restarting the cycle.

Biotic factors also include the behaviors of living organisms that directly or indirectly affect the environment. Sometimes these behaviors and effects may be viewed on a large scale. For example, scientists may study predation, or the ways animals eat other animals, or urbanization, the building of cities by humans. Other times these behaviors are small and localized. Big or small, these behaviors and effects are biotic factors.

Abiotic Factors

The word abiotic comes from Greek words meaning "without life." The abiotic factors in an ecosystem include all things that are inanimate, or never alive. In the analogy of the house, the abiotic factors would include the structural parts of the house itself and the furniture, appliances, and other nonliving objects within the house.

In nature, abiotic factors are many and varied. The largest abiotic factors are the fundamental components of Earth's physical makeup, including the lithosphere, hydrosphere, and atmosphere. The
lithosphere
is all of Earth's rock collectively, ranging from rocks locked in the planet's interior to mountains that have emerged on the surface. The
hydrosphere
includes all the world's surface water, fresh and salty. The
atmosphere
is the mass of air that surrounds Earth. These factors are extremely important, but they are not alive, so they are considered abiotic.

Other important abiotic features include sunlight, needed for its warmth and brightness; water, necessary for sustaining life and carrying out various natural cycles; oxygen, which allows living things to breathe; and soil, which helps biotic plants grow and later helps to decompose them after they die. Features such as climate and temperature; topography, or the landforms of an area; the altitude or height of an ecosystem, which can affect temperature, climate, and air thickness; the type of rocks nearby; and the availability of water are also significant abiotic factors.

Interrelationship of Factors

Almost all features of an ecosystem are interrelated in some way, which means they work together to keep the ecosystem in balance. Generally, the abiotic features create the natural settings for the biotic features and dictate how organisms must live in a given ecosystem. For example, abiotic factors such as high temperatures and dryness require living organisms that can tolerate heat and learn to store water to survive. In this way, abiotic features create limitations on the kinds and quantities of biotic factors that can live in an ecosystem. Biotic factors have the option of living in an ecosystem and adapting to its conditions or moving along to a more favorable ecosystem.

The delicate interrelationship of biotic and abiotic factors becomes clear in many cases due to human actions in an ecosystem. For example, phosphorous is a natural abiotic material that forms in rocks and helps to make soil healthy. When humans mine large amounts of phosphorous to use as fertilizer, the excess of this material may lead to negative effects in soil and nearby bodies of water and endanger the biotic factors in these places. Another example is the human use of abiotic rock salt on icy roads, which, when used too frequently, can lead to increased salt levels in nearby bodies of water and disrupt biotic factors in the water. Any alteration to a natural cycle will likely have effects on the interrelated biotic and abiotic factors.

Bibliography

"Abiotic and Biotic Factors." Assignment Discovery. Discovery Channel. Web. 18 Dec. 2014. http://www.discovery.com/tv-shows/other-shows/videos/assignment-discovery-shorts-abiotic-and-biotic-factors/

"Biotic and Abiotic Factors." Ecology Disrupted. American Museum of Natural History. Web. 18 Dec. 2014. http://www.amnh.org/explore/curriculum-collections/ecology-disrupted/winter-roads/lesson-plans/ecology-disrupted/biotic-and-abiotic-factors

Buckley, James M. "Biotic vs. Abiotic." Regents Prep. Oswego City School District Regents Exam Prep Center. Web. 18 Dec. 2014. http://regentsprep.org/regents/biology/units/ecology/biotic.cfm

"Discovery File: Abiotic and Biotic Factors." Yale Peabody Museum of Natural History. Yale University. Web. 18 Dec. 2014. http://peabody.yale.edu/sites/default/files/documents/education/Abiotic%20and%20Biotic%20Factors%20DF.doc

Morrow, Angela, and Tim Ligget. Cracking the AP Environmental Science Exam, 2010 Edition. New York: Random House, Inc. / The Princeton Review, 2009, 58–62, 67–69. Print.