Biotic Factors


Biotic Factors Definition

Biotic factors are the living parts of an ecosystem.

Because of the way ecosystems work – as complex systems of competition and cooperation, where the action of every life form can effect all the others – any living thing within an ecosystem can be considered a biotic factor.

Biotic factors such as soil bacteria, plant life, top predators, and polluters can all profoundly shape which organisms can live in an ecosystems and what survival strategies they use.

Biotic factors, together with non-living abiotic factors such as temperature, sunlight, geography, and chemistry, determine what ecosystems look like and what ecological niches are available.

Types of Biotic Factors

Biotic factors are grouped by scientists into three major groups, which define their role in the flow of energy which all living things in the ecosystem need to survive. These groups are producers or autotrophs, consumers or heterotrophs, and decomposers or detritivores.


Producers – also known as autotrophs, from the Greek words “auto” for “self” and “troph” for “food” – are organisms that make their own food using inorganic materials and energy sources.

Producers are extremely important: without them, no life could exist at all!

The very first life forms on Earth had to learn to make fuel and building materials to make more cells out of non-living materials. That’s because when the first life forms appeared, there were no other life forms to feed on! So the first life forms had to be producers. Producers remain vital today as the life forms that can harness inorganic energy to be used as fuel for life.

There are two major classes of producers:

1. Photoautotrophs are by far the most common type of producer on Earth today. These producers harness energy from sunlight to power their life functions. Green plants, green algae, and some bacteria are photoautotrophs.

Most photoautotrophs use a pigment, such as chlorophyll, to catch photons from the Sun and harvest their energy. They then package that energy into a form that all life forms can use, and use it to create proteins, sugars, lipids, and more essential materials for life.

In most ecosystems, plants – which are producers that are multicellular, highly complex, and very efficient at turning sunlight into fuel for living organisms – form the bottom of the energy pyramid. All other organisms depend on the energy plants harvest from the Sun to survive.

2. Chemoautotrophs are fairly rare in most ecosystems. They obtain energy from chemicals such as hydrogen, iron, and sulfur, which are not common in most environments. Nonetheless, they can still play an important role in ecosystems because of their unusual biochemistry.

Some methanogens – microorganisms that make methane – are chemoautotrophs. Methane, a greenhouse gas which is much more powerful than carbon dioxide, may play a major role in regulating the planet’s temperature. Other chemoautotrophs can produce similarly powerful chemicals with their unique metabolisms.

It is actually not known whether the first forms of life on Earth were photoautotrophs or chemoautotrophs. Photoautotrophs are more common today, but that may simply be because sunlight is more plentiful than the chemicals chemoautotrophs use as their energy source.


Consumers, also called “heterotrophs,” are organisms that eat other living organisms in order to obtain energy. Their name comes from the Greek “hetero” for “other” and “troph” for “food.”

Herbivores who eat plants, carnivores who eat animals, and omnivores who eat both plants and animals, are all heterotrophs.

Heterotrophy probably evolved when some organisms discovered that they could eat autotrophs as a source of energy, instead of creating their own energy and organic materials.

Some autotrophs subsequently evolved symbiotic relationships with consumers, such as angiosperms – plants which produce nectars and fruits to attract animals, who ultimately help them to reproduce.

Most levels of most ecosystems’ energy pyramids consist of consumers – herbivores, minor predators, and top predators who eat other organisms.


Decomposers, or detritovores, are organisms that use organic compounds from producers and consumers as their source of energy. They are important to ecosystems because they break down materials from other living things into simpler forms, which can then be used again by other organisms.

Decomposers include soil bacteria, fungi, worms, flies, and other organisms that break down dead materials or waste products from other life forms. They are distinct from consumers, because consumers usually consume other organisms while they are still alive.

Decomposers, on the other hand, metabolize waste products that might not be of interest to consumers, such as rotting fruit and dead animals. In the process they break down these dead things into simpler chemicals that can be used by heterotrophs to thrive and produce more energy for the ecosystem as a whole.

This is the principle behind the practice of composting – where waste scraps of plants and animal products are put into a pile, where decomposers such as bacteria, worms, and flies are allowed to thrive. These decomposers turn the waste products into rich fertilizer for the composter’s garden, which then grows bigger and healthier thanks to the decomposers breaking down the waste products in the compost.

Decomposers are the link between the bottom of an ecosystem’s energy pyramid and the other levels. Decomposers can take energy and raw materials from dead plants, herbivores, lesser carnivores, and even top carnivores, and break it down into a form that can be used by the ecosystem’s producers to make it easier for them to harness sunlight. In this way, the ecosystem’s energy cycle is preserved.

Examples of Biotic Factors

Example #1: Cyanobacteria and Life on Earth

Scientists believe that the earliest widespread form of life on Earth was cyanobacteria. These fairly simple cells, which made food and organic materials from sunlight, played a massively important role in creating all of Earth’s modern ecosystems.

Prior to the success of cyanobacteria, Earth did not have an oxygen atmosphere. That meant that aerobic respiration was not possible – and also meant that it was impossible, or very difficult, for any organisms to live on land because of the DNA-destroying ultraviolet radiation from our sun.

However, cyanobacteria developed a method for storing the energy of sunlight in organic molecules. For this they needed to take molecules of carbon from inorganic sources, such as carbon dioxide in the air, and turn them into carbon-based organic compounds such as sugars, proteins, and lipids.

To achieve this, cyanobacteria took in the inorganic gas CO2, and released a new gas, O2.

O2, or molecular oxygen turned out to be the perfect fuel for the most powerful type of heterotroph metabolism: aerobic respiration. Molecules of O2 also reacted with ultraviolet light in the upper atmosphere to form, O3 – a molecule also known as ozone, which absorbed ultraviolet light in the upper atmosphere and made it safe for life forms to colonize land.

In the billions of years to come, cyanobacteria would be mostly replaced by its more sophisticated descendants such as trees, grass, and algaes who would take over its role as Earth’s primary oxygen producers. However, cyanobacteria itself still appears in blooms which can sometimes be seen from space!

2010 Filamentous Cyanobacteria Bloom near Fiji

2010 Filamentous Cyanobacteria Bloom near Fiji

As biotic factors, cyanobacteria and its modern descendants supplied not only energy and organic compounds, but also oxygen, to all of Earth’s ecosystems!

Example #2: Wolves in North America

When European colonists arrived in North America, wolves were common in many of the continent’s ecosystems. These large carnivores were the top predators in many places, using a combination of their large size and teamwork to take down large prey animals.

The colonists and their descendants hunted wolves fiercely, due to safety concerns over the fact that wolves could eat sheep that farmers depended on for food, and could even eat human children.

However, the disappearance of wolves eventually started to cause new problems for the humans of North America. Without their top predator, deer and other herbivore species multiplied to unprecedented numbers.

This might have seemed nice for human hunters who ate deer meat and sold deer skins at first, but the problem became serious when the deer started eating so many plants that crops, gardens, and wild plant species became endangered. Humans began to have to hunt deer themselves, not just for meat and skin, but to prevent serious damage to their ecosystems.

Humans didn’t realize the full extent of the roll of wolves until a ban on wolf hunting was introduced, and wolves bred in captivity were released back into the wild to repopulate the wolf species in some areas.

The areas where wolves were re-introduced underwent startling transformations. Numbers of deer and other large prey species went down, sure enough – which led to populations of many plant species increasing.

To the surprise of human scientists studying the ecosystems, even land forms began to change: it turned out that deer had been eating grass and other small plants whose root systems held soil in place against erosion. With wolves keeping the deer population in check, the plant populations began to come back – and erosion decreased, and the courses of rivers changed! Fish were also effected by a decrease in loose soil washing into the river.

This is an excellent example of how complex and interconnected ecosystems are – and how the removal of one element of the ecosystem, even if its only role is to eat other animals, can cause big changes for all other organisms living in the ecosystem.

Example #3: Humans

In 2016, biologists around the world decided to declare that the Earth had entered a new geologic era: the Anthropocene.

The name “Anthropocene” comes from the Greek words “anthropo” for “human” and “cene” meaning “new” or “recent.”

This era is defined by the effects of human technology, which has caused massive changes to the global ecosystem on par with the effects of past major climate change events and even asteroid impacts.

Human activity has drastically changed the carbon cycle of Earth, with the burning of wood, coal, and oil releasing millions of years worth of carbon dioxide into the atmosphere in the space of just a couple of centuries. Over the same time scale, humans have cut down about half of all Earth’s forests, which had previously acted to take carbon dioxide out of the air and incorporate it back into plant life.

In addition, humans have begun to release many new substances into Earth’s land, air, and oceans, including plastics, heavy metals, and radioactive materials, none of which exist in nature.

The result has been the beginning of alarmingly rapid climate change and a mass extinction, in which species are disappearing faster than they have been since the asteroid impact that killed the dinosaurs and made way for the rise of mammals 65 million years ago.

Humans are therefore maybe the most powerful example of how the living factors in an ecosystem can change it since cyanobacteria.

This has led some environmentalists to suggest that humans are “evil,” and “bad for the Earth. But the truth is that the Earth always survives ecological upheavals. It’s just a question of whether the species that exist at their beginning survive to their end.

That’s why many scientists say humans should be concerned about their effect on the planet. Not because changing the planet is in itself morally wrong, but because humans themselves rely on the complicated ecological interplay of thousands of species for their food.

Scientists are already beginning to raise alarms that the pollinators on which many human food crops depend appear to be dying off due to new chemicals that humans have released to the environment.

Human food crops are also threatened by climate change caused by the carbon dioxide humans have released into the air, which has brought severe drought to many areas with dense human populations who require large amounts of food to survive.

Medical scientists also caution that man-made climate change is allowing dangerous insect-borne diseases, which used to be restricted to the regions near the equator, to spread to new areas.

As the dominant species on Earth, it is important that humans learn about the ecosystems upon which they depend for well-being and survival. We have the power to seriously disrupt these ecosystems – and as living things which rely on other life forms for our own survival, we may set in motion events that could lead to our own extinction if we are not careful.

Related Biology Terms

  • Ecosystem – A community of organisms, and their physical environment.
  • Energy Pyramid – A diagram which shows the flow of energy through organisms in an ecosystem.

Test Your Knowledge

1. Which of the following is not an example of a producer, or autotroph?
A. Cyanobacteria
B. A daisy
C. A wolf
D. A chemoautotroph

Answer to Question #1

2. Which of the following is not an example of decomposers in action?
A. A fruit fly laying eggs in a rotting fruit
B. A compost pile turning food scraps into fertilizer
C. Mushrooms growing on a piece of dead wood
D. A venus fly trap consuming a fly

Answer to Question #2

3. Which of the following is an example of major ecosystem change that was NOT caused by biotic factors?
A. The release of oxygen into the atmosphere, allowing aerobic respiration and the colonization of dry land.
B. The rise in global temperatures during the 20th century, caused by the release of large quantities of carbon dioxide.
C. The extinction of the dinosaurs following the impact of an asteroid in the Yucatan peninsula.
D. All of the above.

Answer to Question #3

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