Biotic and Abiotic Factors in an Ecosystem

Seagrass and fish in water, Santa Cruz Island, California, USA
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In ecology, biotic and abiotic factors encompass all the living and non-living parts of an ecosystem. Biotic factors pertain to living organisms and their relationships. Abiotic factors are the non-living components of the ecosystem, including sunlight, water, temperature, wind, and nutrients. 

Interactions between biotic and abiotic factors ripple through an ecosystem. Plants, for example, use sunlight, water, and carbon dioxide to produce energy and grow, releasing oxygen and — directly or indirectly — serving as a food source for other organisms. When they die, living organisms break back down into abiotic components. Changes in a biotic factor, such as a species population increase, or an abiotic factor, such as a decrease in precipitation, can therefore affect the entire ecosystem. 

Ecologists use biotic and abiotic factors to predict population changes and ecological events. By investigating how these factors interact, ecologists can gauge what is happening in an ecosystem over time. Ecologists may conduct population surveys to see whether the number or density of a given species is changing, how quickly it is changing, and why. By understanding the biotic and abiotic factors that impact the species, they can find explanations for population declines or increases. In addition, they may be able to predict ecological events like species die-offs, over-population, changes in growth rates, and disease outbreaks. 

Biotic Factors

Biotic factors include interactions between organisms, like disease, predation, parasitism, and competition among species or within a single species.  In addition, living organisms themselves are biotic factors. They fall into three main categories: producers, consumers, and decomposers.

  • Producers: These organisms, which include plants and algae, convert abiotic factors into food. Most producers use the sun’s energy along with water and carbon dioxide in a process called photosynthesis. This results in energy that producers can feed on. In fact, producers are also called autotrophs, because they feed themselves: In Greek, “auto” means self, and “troph” means feed or nourishment. Autotrophs make use of abiotic factors to produce their own food. 
  • Consumers: Most consumers are animals, and they do not make their own food. Instead, they consume producers or other consumers to obtain food energy. That’s why consumers are also known as heterotrophs: “hetero” means different or other, because they obtain their nourishment from species other than themselves. Consumers can be herbivores, carnivores or omnivores. Herbivores feed on producers; they include animals like horses, elephants, and manatees. Carnivores feed on other consumers. They include lions, wolves, and orcas. Omnivores, such as birds, bears, and lobster, feed on both producers and consumers.  
  • Decomposers: These are the organisms that break down organic matter from dead plants and animals into the inorganic components, like carbon and nitrogen, that are necessary for life. The inorganic matter then returns to the soil and water as nutrients that can be used by producers anew, continuing the cycle. Decomposers are also called saprotrophs: from the Greek “saprós,” or rotten, because they feed on rotting organic matter. Examples of decomposers include bacteria, fungi, earthworms, and some insects.

Abiotic Factors

Abiotic factors are the non-living components of the ecosystem, including its chemical and physical factors. Abiotic factors influence other abiotic factors. In addition, they have profound impacts on the variety and abundance of life in an ecosystem, whether on land or in water. Without abiotic factors, living organisms wouldn’t be able to eat, grow, and reproduce. Below is a list of some of the most significant abiotic factors.

  • Sunlight: As the world’s biggest source of energy, sunlight plays an essential role in most ecosystems. It provides the energy that plants use to produce food, and it affects temperature. Organisms must adapt depending on how much access they have to sunlight.
  • Oxygen: Oxygen is essential to the majority of life forms on Earth. The reason? They need oxygen in order to breathe and to release energy from food. In this way, oxygen drives the metabolism of most organisms.  
  • Temperature: The average temperature, range of temperature, and extremes of temperature in both air and water are all important in how organisms live and survive in an ecosystem. Temperature also affects an organism’s metabolism, and species have evolved to thrive in the typical temperature range in their ecosystem
  • Wind: Wind can exert many effects on an ecosystem. It moves other abiotic factors, like soil and water. It disperses seeds and spreads fire. Wind affects temperature as well as evaporation from soil, air, surface waters, and plants, changing humidity levels.
  • Water: Water is essential for all life. In terrestrial (land) ecosystems where water is scarce, such as deserts, organisms develop traits and behaviors that help them survive by harvesting and storing water efficiently. This can sometimes create a water source for other species as well. In ecosystems like rainforests where the abundance of water depletes soil nutrients, many plants have special traits that let them collect nutrients before water washes them away. Water also contains nutrients, gases, and food sources that aquatic and marine species depend on, and it facilitates movement and other life functions. 
  • Ocean currents: Ocean currents involve the movement of water, which in turn facilitates movement of biotic and abiotic factors like organisms and nutrients. Currents also affects water temperature and climate. They play an important role in the survival and behavior of organisms that live in water, since currents can influence things like food availability, reproduction, and species migration.
  • Nutrients: Soil and water contain inorganic nutrients that organisms require to eat and grow. For example, minerals like phosphorous, potassium, and nitrogen found in soil are important for plant growth. Water contains many dissolved nutrients, and soil runoff can carry nutrients to aquatic and marine environments. 

What About Soil?

Composed of both biotic and abiotic components, soil is an interesting case. Soil filters and stores water and anchors the roots of plants. It contains nutrient minerals and gases, as well as millions of microorganisms like bacteria, fungi, and single-celled organisms called archaea. These are important decomposers, the planet’s indispensable recyclers. 

The Relationship Between Biotic and Abiotic Factors

Both biotic and abiotic factors can influence and constrain a species’ population. Factors in an ecosystem that inhibit biotic operations like population growth are called limiting factors

Consider the difference between life in ocean surface waters and a deep ocean ecosystem 13,000 feet below. Near the ocean’s surface, tiny plants called phytoplankton convert the ample sunlight into energy. The phytoplankton form the base of a vast food web that a multitude of other species depend on, from dolphins and fish to the diverse organisms that compose coral reefs. Waters are warmer near the surface, and there is more oxygen. These abiotic factors of sunlight, oxygen, and temperature, among others, affect the characteristics and behavior of organisms in the entire ecosystem. 

By contrast, little to no sunlight permeates deep ocean waters; the only light is produced by the creatures that live there. At these depths, organisms must be adapted to extreme pressure, which is more than 100 times greater than surface waters. Life here must withstand temperatures close to freezing. There is less food and less oxygen, which requires slower metabolisms. In this ecosystem, the low levels of light, oxygen, and food, along with cold water temperatures, are limiting factors that constrain the organisms that live here. 

Abiotic factors have profound impacts on the variety and abundance of life in an ecosystem, whether in water or on land. But it works both ways: Biotic factors can also alter abiotic factors. All that phytoplankton in the ocean produces an abundance of oxygen. Larger plants, like kelp forests, filter sunlight, cool the waters, and affect ocean currents. 

On land, too, biotic factors trigger changes that can move through an ecosystem. For example, a study in Yellowstone National Park found that during the decades in which grey wolves were absent from the park, elk didn’t move around as much because they had fewer predators. Instead, elk browsed on woody plants and shrubs near streams, reducing the number and size of willow trees along stream banks. Fewer willows meant less food for beavers, whose population then declined. Fewer beavers meant fewer beaver dams, which in turn decreased marshy habitat for willows and the other species they supported. 

The reintroduction of wolves in 1995 was a turning point. It triggered a possible trophic cascade, an event in which changes in the food web alter the structure of an ecosystem. In this case, the wolves limited the population and behavior of the elk, consequently improving other organisms’ chances of survival. The elk stopped spending as much time hanging around streams. The willow and beaver populations began to recover, and beavers built more dams. This changed the course of streams, restoring wetlands. The reintroduction of the wolf was a limiting factor on the elk. As a result, other biotic communities rebounded, in part because the wolves indirectly influenced an important abiotic factor: water.

Ecologists also study relationships between biotic and abiotic factors to make predictions about biotic populations. Understanding how the wolf reintroduction in Yellowstone influenced other factors, researchers can anticipate how future changes to wolf populations might affect the ecosystem. 

Studying these relationships can also be useful in controlling invasive species. Another recent study investigated which biotic and abiotic factors most affect wild pigs, an invasive mammal present on five continents. 

Using models that generated data about wild pigs’ interactions with factors like water availability, temperature, plant productivity, predation, and human-caused land use change, the researchers created a global map predicting wild pig population densities. Identifying the factors most closely associated with population density is aiding in the management of this invasive species. Using such approaches, ecologists can devise ways to protect ecosystem biodiversity.

Takeaways

  • Biotic and abiotic factors are all the living and non-living components of an ecosystem.
  • Biotic factors include not only living things but interactions between organisms, such as predation, parasitism, and competition.
  • Abiotic factors include non-living components, as well as chemical and physical factors, that living organisms require in order to thrive. 
  • When an abiotic or biotic condition in an ecosystem limits the growth or size of a population, it is referred to as a limiting factor.
  • Ecologists study relationships between biotic and abiotic factors to predict population changes and ecological events.
View Article Sources
  1. Beyer, Hawthorne L. et al. "Willow on Yellowstone's Northern Range: Evidence for a Trophic Cascade?" Ecological Applications, vol. 17, no. 6, 2007, pp. 1563-1571., doi:10.1890/06-1254.1

  2. Lewis, Jesse S. et al. "Biotic And Abiotic Factors Predicting The Global Distribution And Population Density Of An Invasive Large Mammal." Scientific Reports, vol. 7, no. 1, 2017, doi:10.1038/srep44152