Abiotic Factors Definition
Abiotic factors are non-living factors in an ecosystem. As part of the ecosystem, these factors do affect the living things in it, but they are not living themselves.
The term “abiotic” comes from the root parts “a-” meaning “without,” and “bio,” meaning “life.” The living parts of an ecosystem are called “biotic factors.”
Examples of Abiotic Factors
Common examples of abiotic factors include:
- Soil composition
- Salinity (the concentration of salt in water)
Abiotic factors make up for much of the variation seen between different ecosystems. By determining the availability of such essential resources as sunlight, water, oxygen, and minerals, abiotic factors determine which organisms can survive in a given place.
What follows are just a few examples of how abiotic factors can shape ecosystems by determining which organisms can live in them, and what those organisms must do to survive.
Example #1: What Makes the Difference between Forests and Plains?
In many places, for example, prairie or savannah ecosystems evolve instead of forest or jungle ecosystems, because there is not enough rain to support trees. Other factors, such as high winds and soil that is poor in essential nutrients, may also help to create an environment in which trees cannot survive but prairie plants are prevalent.
Abiotic factors may also include added challenges to life forms, such as temperature extremes, high winds, or even pollution. Indeed, human pollution has become an important factor in determining which life forms survive in some ecosystems.
Example #2: Pollution and the Peppered Moth
In the United Kingdom two types of moths were found at the beginning of the 19th century. By far the most common was the white-bodied peppered moth, whose black-speckled white body allowed it to blend in with tree bark to avoid being eaten by birds.
During the Industrial Revolution, however, coal-burning plants in cities in the United Kingdom produced massive amounts of ash, which covered the surrounding forests.
As a consequence, white-bodied moths now stood out against the dark tree trunks, but black-bodied moths, who had once been at a disadvantage against the pale tree bark, could now hide more effectively.
Naturalists studying the peppered moth found in subsequent decades that black-bodied moths were dominant near cities with factories, whereas white-bodied moths remained dominant in the soot-free forests of rural areas.
Example #3: Desert Abiotic Factors
Perhaps the most obvious biome that is determined by abiotic factors is the desert. Because of their low rainfall, deserts develop ecosystems very different from those of any other habitat.
Scientists use the term “desert” to refer to any area which has less than 25cm, or 9.75 inches, of rain or snow in an average year. By this definition, deserts cover about 20% of Earth’s land area, including the continent of Antarctica.
Desert ecosystems can also experience extreme temperature swings, because open water and water vapor act as temperature stabilizing elements in wetter biomes.
Between the low rainfall and the often extreme temperatures, deserts develop unique organisms and food chains.
Example #4: Tropical Rainforest Abiotic Factors
At the other end of the spectrum of biomes, tropical rainforests are one of the wettest ecosystems on Earth. To be classified as a rainforest, an area must receive at least 75 inches (190cm) of rain per year. Most rainforests get well over 100 inches (254cm) annually.
Tropical rainforests are rainforests located in the tropics. The tropics form a belt around the equator and receive a great deal of sunlight throughout the year, resulting in warm temperatures and mild seasons.
Due to their warm, wet climates, rainforests develop extremely dense, lush, and complex ecosystems. Rainforests are unique in that they consist of life layered on top of life – most scientists divide tropical rainforests into six different layers, each of which hosts different types of life!
The topmost layer of the rainforest, or “canopy” receives the most sunlight, while the bottom-most layers receive very little sunlight because of shade from plants in the other layers.
Example #5: Tundra Abiotic Factors
Tundra is another unique type of biome that is created by abiotic factors.
Tundras are located in the north polar region, where they receive so little light and heat from the sun that only a thin, top layer of soil thaws sufficiently to allow plant growth. A deep layer of soil, called subsoil, can remain frozen for thousands of years.
Because the subsoil remains frozen, trees, which require deep roots, cannot grow in the tundra. Instead, grasses and other small plants which can grow in the thin soil flourish.
Example #6: Abiotic Factors in the Ocean
The ocean plays host to some unique abiotic factors. For one thing, the ocean contains salt. For another, it has the attribute of depth, which effects the amount of sunlight that sea life receives.
The saltiness of the ocean is quite important for the animals living there. All of them must adapt to prevent the ocean’s salt from disrupting their biochemistry. Dolphins that swim in the ocean get all of their water from their prey animals, because the salt water would dehydrate them if they drank it. Some fish, in fact, can survive only in salt water because they have adapted so well to the environment.
The ocean, like the rainforest, also has a number of different zones which receive different amounts of sunlight, and host very different types of life. This is because water itself both blocks out and absorbs sunlight.
Life in the topmost zone of the ocean, called the epipelagic zone, receives a large amount of sunlight. This is where photosynthetic ocean life, like coral and seaweed, is found.
The abyssopelagic zone at the bottom of the ocean, by contrast, receives almost no sunlight. This part of the ocean hosts strange sea creatures, some of whom actually cannot survive at the surface because their body structures depend on the high water pressure at depth.
The very deep trenches of the ocean contain an even colder, darker zone called the “hadeopelagic.” This zone is named after the Greek underworld.
Related Biology Terms
- Biome – A large, naturally occurring community of life forms. Biomes can be thought of as “types of ecosystems.” Rainforest, tundra, savanna, temperate forest, and temperate grassland are examples of biomes.
- Biotic factor – A living element of an ecosystem, such as a plant, animal, or bacteria. Biotic and abiotic factors together make up an ecosystem.
- Convergent evolution – Occurs when unrelated life forms evolve very similar solutions to environmental problems.
- Ecosystem – A biological community of organisms and their environment. “Ecosystem” and “biome” are very similar terms, although “biome” usually refers to a specific type of ecosystem such as a rainforest, tundra, etc.
- Energy Pyramid – A graphic illustration which is used to show how energy flows through an ecosystem. These pyramids typically have plants, which efficiently and directly harvest sunlight, at the “bottom” and the top predator at the top, with herbivores and intermediate prey species in the middle.
Test Your Knowledge
1. Which of the following is abiotic factor?
A. Trees and temperature
B. Trees and rainfall
C. Bacteria and predators
D. Temperature and rainfall
2. The only difference between desert and tropical rainforest is the amount of rainfall.
3. Human activity can create new abiotic factors.