Biotic and abiotic factors are the two components of an ecosystem. Biotic factors are the living things, like plants, animals, and fungi. Abiotic factors are non-living things, like air, soil, water, and sunlight. Every ecosystem includes both biotic and abiotic factors. Abiotic factors determine the type of life that lives in the ecosystem.
Biotic factors are any organisms in an ecosystem. Basically, if you see it in the kingdom of life, it’s a biotic factor. So, biotic factors include plants, animals, algae, fungi, lichens, bacteria, and protists. Specific examples include humans, trees, grass, cats, E. coli, frogs, and mushrooms. One way of classifying biotic factors is by their nutritional needs:
- Producers or Autotrophs: Producers or autotrophs make their own food from abiotic factors. The most common pathway is photosynthesis, which converts carbon dioxide, water, and sunlight into the sugar glucose. Plants, algae, and some protists are producers.
- Consumers or Heterotrophs: Consumers or heterotrophs get their nutrients by eating producers or other consumers. Herbivores, like cattle, only feed on producers. Carnivores, like wolves and cats, only feed on other consumers. Omnivores, like humans and dogs, consume both producers and other consumers.
- Decomposers or Detritivores: Decomposers are heterotrophs that do not make their own food. The distinction is that they digest compounds made by producers and consumers. Food sources for decomposers include dead and decaying producers and consumers and the waste products made by living organisms. Examples of decomposers are fungi, earthworms, and certain bacteria.
Abiotic factors are nonliving parts of an ecosystem. Examples of abiotic factors include:
- Air and wind
- Rocks and minerals
- Natural events, like wildfires, floods, volcanic eruptions, and earthquakes
Abiotic factors affect biotic factors, plus they also influence other abiotic factors. For example, a drought influence the amount of water in an ecosystem. The pH affects how rocks and minerals break down and the nutrients available within the system.
Examples of Biotic and Abiotic Factors in an Ecosystem
Now that you understand the difference between biotic and abiotic factor in an ecosystem, let’s identify them in ecosystems.
For example, consider an aquarium that contains fish and plants.
- Bacteria in the water, rocks, and filtration system
- Algae, fungi, protozoa, and other organisms that are either parasites on/in the fish or plants or that enter the ecosystem with water changes or from the air
- Waste released by the fish
- Fish food
Fish urine and feces and fish food is not exactly alive, but it is organic. It also contains bacteria. Viruses, if present, are also usually included as biotic factors.
- pH and minerals within the water
- The container
- Rocks, sand, or whatever is on the bottom of the tank
- Filtration media
- Air, possibly including a bubbler
Another small ecosystem is a houseplant.
- Algae, fungi, bacteria and other microorganisms associated with the plant, water, air, and soil
- Possibly insect pests that travel through the air
- Light (including its source, intensity, and duration)
- Fertilizer (probably)
- Soil and water pH
- The pot that contains the plant and soil
- Sounds and vibrations
You may think of additional biotic and abiotic factors in an aquarium or potted plant ecosystem. Larger, more complex ecosystems have many more biotic and abiotic factors.
A limiting factor is a biotic or abiotic factor that restricts the growth of an ecosystem. At any given time, there is only one limiting factor. But, the factor often changes.
For example, consider an ecosystem where a plant grows on a windowsill. What one factor determines the plant’s health? Usually, this is the amount of water the plant receives. Over time, the limiting factor changes, perhaps becoming the amount of light the plant receives or the nutrients in its soil.
As another example, consider the rainforest floor. Usually, the limiting factor is the amount of sunlight that reaches the surface through the tree canopy. Plants compete for this light. Animals depend on the success of the plants. Fungi thrive on the moisture and limited light. In the dry season, the limiting factor may change to the amount of rainfall that falls. Or, the temperature may rise or drop, and become the new limiting factor.
- 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.