Biotic and Abiotic Factors

What Are Biotic and Abiotic Factors in an Ecosystem?

Biotic Factors

Biotic factors are living organisms within an ecosystem, for example, animals, plants, and fungi. There are three main types of biotic factors: autotrophs, heterotrophs, and detritivores.

• Autotrophs are organisms that produce their own food.

  • Plants and algae, for example, use sunlight to produce food from carbon dioxide and water (a process called photosynthesis).

  • Other organisms like bacteria produce food using chemicals instead of sunlight as the energy source (chemosynthesis).

• Heterotrophs are organisms that consume other organisms.

  • Herbivores like deer and cows feed on plants.

  • Carnivores like lions and tigers feed on other animals.

  • Omnivores like humans and pigs feed on both animals and plants.

• Detritivores are heterotrophs that consume dead or decaying organisms. By breaking down dead and decaying material into inorganic nutrients, detritivores contribute to nutrient cycling in an ecosystem.

  • Examples of detritivores are earthworms, maggots, sea cucumbers, and crabs.

Abiotic Factors

Abiotic factors are non-living chemical and physical environmental conditions within an ecosystem. Examples include temperature, water, wind, light, and chemical composition.

How Do Biotic and Abiotic Factors Influence the Adaptation of Species?

Biotic and abiotic factors are selection pressures. The interaction of organisms with biotic and abiotic factors can affect their evolutionary fitness. Selection pressures can increase or decrease the occurrence of a trait in a population of organisms at a given time.

Traits that help organisms survive and reproduce in their specific environments are called adaptations. Species with favorable traits that survive in their environment can reproduce more because of those traits; this is natural selection. Over time, those with favorable traits will outnumber those without them, eventually changing the heritable traits of the entire population of a species, a process called evolution.

How Do Biotic Factors Influence The Adaptation of Species?

Living organisms interact in ways that affect each other’s survival and reproduction. Interactions between biotic factors can be divided into five main types of ecological relationships: competition, predation, commensalism, mutualism, and parasitism.

Competition

For example, plants tend to compete for sunlight as it serves as their primary energy source. In rainforests, tall, old-growth trees reach out to the sun, and their branches form the canopy--the uppermost layer of the forest habitat--and block out the sun.

When an old-growth tree falls, a gap forms in the canopy, and the plants in the layers below rush to maximize the sun exposure. Some are adapted to avoid shade through the elongation of their stem or petioles. Others can tolerate shade by increasing the surface area of their leaves.

Predation

Let’s take the predatory relationship between lions and zebras (Fig. 1) as an example. Traits that help zebras escape or hide from lions (like speed and camouflage) increase their chances of survival. On the other hand, lions have adapted to their prey's increased size and strength by stalking and hunting in groups. More intelligent lions can use better tactics to corner their prey, so they have better chances of feeding and surviving.

Fig. 1 Lions stalk their prey and hunt in groups.

Commensalism

An example of this is the remora (family Echineidae), that have a flat disk-like structure that allows it to attach itself to sharks and other fishes, giving it access to a free ride and a free meal since it feeds on the leftovers of its host (Fig. 2).

Fig. 2 A remora gets a free ride from a whale shark.

Parasitism

For example, female brown-headed cowbirds (Molothrus ater) lay their eggs in the nests of other birds, including the savannah sparrow (Passerculus sandwichensis) (Fig. 3). Because the savannah sparrow cannot tell the fledglings apart, they take care of all of them, including those of the cowbirds. Cowbirds are much larger than the savannah sparrow, so they eat more food than the other fledglings.

Fig 3. The brown-headed cowbird fledgling is larger than the savannah sparrows fledglings.

Mutualism

Interactions between flowering plants and their pollinators are a good example of mutualism. Most flowering plants are pollinated by animals such as birds and insects. This interaction helps flowering plants to reproduce and diversify. On the other hand, pollinators get to eat pollen or nectar. Other pollinators like bees can also use waxes to build their hives and certain compounds to attract mates.

As a result of this relationship, flowering plants could benefit from traits that attract pollinators. For example, some flowering plants adapt by producing pigment that gives them a bright color which is attractive to some pollinators, like hummingbirds. On the other hand, hummingbirds adapt to the flowers available in the ecosystem through their different beak lengths and shapes.

How Do Abiotic Factors Influence the Adaptation of Species?

Abiotic factors also play a major role in the ecosystem. Abiotic factors can limit or enhance the ability of organisms to survive and reproduce. Over time, organisms inherit adaptations that suit their environmental conditions.

Abiotic factors like wind and water can aid in dispersing pollen and seeds, helping plants reproduce. For example, the dipterocarp fruit (Fig. 4) has "wings" that allow it to use the wind draft to spread as far as possible.

Fig. 4 Dipterocarp fruit. Dipterocarps (which literally translates to “two-winged fruits) are tall trees usually found in tropical rainforests.

Abiotic factors like temperature, salinity, and water pH can greatly affect marine life. Coral bleaching, for instance, occurs when the water temperature gets too high (Fig. 5).

Fig. 5 Coral and microscopic algae depend on each other for survival. When water temperatures get too high, the microscopic algae leave the coral tissue and the coral slowly dies.

Comparing and Contrasting Biotic and Abiotic Factors

Let's look at some similarities and differences between biotic and abiotic factors.

Similarities Between Biotic and Abiotic Factors

Biotic and abiotic factors are both components of an ecosystem that interact and influence the adaptation of a species by increasing or decreasing its chances of survival and/or reproduction.

Differences Between Biotic and Abiotic Factors

The main difference between biotic and abiotic factors is that biotic factors are comprised of living things (such as plants, animals, and fungi). In contrast, abiotic factors are comprised of non-living chemical and physical environmental conditions in an ecosystem (such as wind, water, and light). Another difference is that biotic factors depend on abiotic factors, while abiotic factors exist independent of biotic factors.

Example of Biotic and Abiotic Factors in an Ecosystem

Let's use a desert ecosystem as an example. What are some biotic and abiotic factors in a desert ecosystem and how do they interact with each other?

Camels, for example, can regulate their body temperature to prevent water loss by sweating. Succulent plants like cacti have spines which are modified leaves that conserve water by preventing water loss during the day and collecting condensed water vapor at night. Cactus seeds also have the ability to stay dormant until there is enough rainfall to support the growth of a seedling.

Temperature and sand are other abiotic factors that could affect plants and animals. Camels have wide feet that help them walk on sand and thick fur that keeps them warm at night. Some lizard species that live in a desert ecosystem have adapted by burrowing into the sand to hide from the intense heat of the sun and by having toes with spiny scales that do not sink in the sand.

Organisms in the desert ecosystem have also made adaptations to biotic factors. For example, succulents have thorns that protect them from herbivores, while camels have thick, leathery mouths that allow them to feed on thorny plants.