Biotic vs. Abiotic Factors in an Ecosystem

In ecology, biotic and abiotic factors make up an ecosystem. Biotic factors are the living parts of the ecosystem, such as plants, animals, and bacteria. Abiotic factors are the nonliving parts of the environment, such as air, minerals, temperature, and sunlight. Organisms require both biotic and abiotic factors to survive. Also, a deficit or abundance of either component can limit other factors and influence an organism's survival. The nitrogen, phosphorus, water, and carbon cycles have both biotic and abiotic components.

Biotic Factors

Biotic factors include any living component of an ecosystem. They include related biological factors, such as pathogens, effects of human influence, and diseases. Living components fall into one three categories:

1. Producers: Producers or autotrophs convert abiotic factors into food. The most common pathway is photosynthesis, through which carbon dioxide, water, and energy from sunlight are used to produce glucose and oxygen. Plants are examples of producers.
2. Consumers: Consumers or heterotrophs obtain energy from producers or other consumers. Most consumers are animals. Examples of consumers include cattle and wolves. Consumers may be further classified as to whether they feed only on producers (herbivores), only on other consumers (carnivores), or a mixture of producers and consumers (omnivores). Wolves are an example of carnivores. Cattle are herbivores. Bears are omnivores.
3. Decomposers: Decomposers or detritivores break down chemicals made by producers and consumers into simpler molecules. The products made by decomposers may be used by producers. Fungi, earthworms, and some bacteria are decomposers.

Abiotic Factors

Abiotic factors are the nonliving components of an ecosystem that an organism or population needs for growth, maintenance, and reproduction. Examples of abiotic factors include sunlight, tides, water, temperature, pH, minerals, and events, such as volcanic eruptions and storms. An abiotic factor typically affects other abiotic factors. For example, decreased sunlight can lower temperature, which in turn affects wind and humidity.

Limiting Factors

Limiting factors are features in an ecosystem that restrict its growth. The concept is based upon Liebig's Law of the Minimum, which states that growth isn't controlled by the total amount of resources, but by the one that is scarcest. A limiting factor may be biotic or abiotic. The limiting factor in an ecosystem can change, but only one factor is in effect at a time. An example of a limiting factor is the amount of sunlight in a rainforest. The growth of plants on the forest floor is limited by light availability. The limiting factor also accounts for competition between individual organisms.

Example in an Ecosystem

Any ecosystem, no matter how larger or small, contains both biotic and abiotic factors. For example, a houseplant growing on a windowsill may be considered to be a small ecosystem. Biotic factors include the plant, the bacteria in the soil, and the care a person takes to keep the plant alive. Abiotic factors include light, water, air, the temperature, the soil, and the pot. An ecologist could seek the limiting factor for the plant, which might be the size of the pot, the amount of sunlight available to the plant, the nutrients in the soil, a plant disease, or some other factor. In a larger ecosystem, like the entire biosphere of Earth, accounting for all of the biotic and abiotic factors becomes incredibly complex.

Sources

• Atkinson, N. J.; Urwin, P. E. (2012). "The interaction of plant biotic and abiotic stresses: from genes to the field". Journal of Experimental Botany. 63 (10): 3523–3543. doi:10.1093/jxb/ers100
• Dunson, William A. (November 1991). "The Role of Abiotic Factors in Community Organization". The American Naturalist. 138 (5): 1067–1091. doi:10.1086/285270
• Garrett, K. A.; Dendy, S. P.; Frank, E. E.; Rouse, M. N.; Travers, S. E. (2006). "Climate Change Effects on Plant Disease: Genomes to Ecosystems". Annual Review of Phytopathology. 44: 489–509. 
• Flexas, J.; Loreto, F.; Medrano, H., eds. (2012). Terrestrial Photosynthesis In A Changing Environment: A Molecular, Physiological, and Ecological Approach. CUP. ISBN 978-0521899413.
• Taylor, W. A. (1934). "Significance of extreme or intermittent conditions in distribution of species and management of natural resources, with a restatement of Liebig's law of the minimum". Ecology 15: 374-379.