Biotic and Abiotic Factors, Practice Problems and FAQs

An ecosystem is a biological community of interacting organisms and their physical environment. It includes abiotic (non living) and biotic (living) components. Do you remember how we classify the living things and non living things? Those which have the characteristics like consciousness, ability to reproduce, and perform the metabolic activities inside can be called as a living organism. Those which are not showing any of these characters are included under the non living things.

Fig: Ecosystem

There are many other characters which can differentiate the living thing from the non living thing. But all the characters that are applicable to the living organisms need the support of the non living things. Some acts of living beings can affect the non living things too. So it is clear that both are interdependent. We are going to discuss more about the biotic and abiotic factors in this article.

Table of contents

• Biotic factors
• Abiotic factors
• Practice Problems
• FAQs

Biotic factors

Those living organisms which can influence the growth and development of other living organisms in the ecosystem are called biotic factors.

Fig: Biotic factors

Classification of biotic factors

The major biotic factors can be classified as follows:

• Producers
• Herbivores
• Carnivores
• Omnivores
• Decomposers

All the biotic factors are related to each other and they can be arranged in different trophic levels depending on the food they eat and the amount of energy they obtain from it.

Fig: Organisms at different trophic levels in a food chain

There are many types of food chains like grazing food chain, detritus food chain etc., on the basis of the organisms involved in it.

Producers

The organisms which can prepare their own food by utilising the energy from the sunlight (photosynthesis) or chemical energy (chemosynthesis) are called producers. Herbs and woody plants are the major producers of a terrestrial ecosystem. The major producers in an aquatic ecosystem are phytoplanktons.

Fig: Producers

Herbivores

The animals which feed on the producers are called herbivores. They are also called primary consumers. In a terrestrial ecosystem, the major herbivores are birds, insects, and mammals. In an aquatic ecosystem the herbivores are molluscs, crustaceans, and protozoans.

Fig: Herbivores

Carnivores

The animals that eat other animals are called carnivores. They eat the meat of other organisms and their diet also includes small insects. Examples are foxes, snakes, sharks etc.

Fig: Carnivores

Omnivores

Those animals that can feed on both animals and plants are called omnivores. They are called the flexible eaters of the Animal Kingdom. Examples include human beings, vultures, dogs etc.

Fig: Omnivores

Decomposers

Decomposers are microorganisms that feed on dead material and break down into simpler substances. They are heterotrophic organisms that convert organic substances into inorganic molecules and form nutrient-rich soil. These are normally microscopic organisms which help in chemically breaking down the complex organic compounds in freshly deposited detritus or fragmented detritus to simpler inorganic minerals or turning them into organic humus. Examples of decomposers include bacteria and fungi. They secrete digestive enzymes on a dead organism which break down dead and waste material into simple and inorganic matter. Decomposers contribute to the recycling of nutrients by adding nutrients to the soil or oceans that producers or autotrophs can utilise. An entirely new food chain is created as a result here.

Fig: Fungi

Detritivores

These are animals which feed on freshly deposited detritus and fragments left over by scavengers and help in fragmenting and pulverising it. These include millipedes, earthworms, beetles, etc.

Fig: Earthworm

Abiotic factors

The physical conditions and non-living resources of the ecosystem which can influence the growth, maintenance and reproduction of a living organism are called abiotic factors. Some of the major abiotic factors are as follows:

• Temperature
• Water
• Light
• Soil

Fig: Abiotic factors

Temperature

The most ecologically important abiotic environmental factor is the temperature. Seasonally from cold winters to hot summers, the average temperature on the land normally varies. It decreases normally from the regions of equator towards the polar regions.

Fig: Temperature variation on Earth

It ranges from sub zero levels at the polar regions and high altitudes to >50℃ in the tropical deserts in the summer. But there are also habitats where average temperatures exceed beyond 100℃. Examples are the deep-sea hydrothermal vents and thermal springs.

Fig: Thermal vent

Examples of effect of temperature on organisms

Depending on temperature, organisms in each region vary. For example, camels cannot sustain low temperatures in cold countries of the arctic region. Similarly polar bears cannot stay in grasslands. Zebras can not survive in extreme cold temperatures. Hornbills which stay in forest cannot survive in deserts.

Fig: Animals in different regions

Classification of organisms based on temperature tolerance

Based on tolerance to temperature, organisms can be classified as follows:

• Eurythermal
• Stenothermal

Eurythermal

Those organisms that can thrive and tolerate a wide range of temperatures are commonly called eurythermal. Examples include sheep, man, cow. These organisms can be found almost all over the world.

Fig: Eurythermal animals

Stenothermal

Those animals that can tolerate only a narrow range of temperatures are called stenothermal. Examples include reptiles, seals etc.

Fig: Stenothermal animals

Water

Water is one of the important factors that influences the life of all living organisms. It is the universal solvent and an important component of protoplasm of the cells. More than 71% of the Earth's surface is covered by water. The availability of water affects most of the flora and fauna and it is different in different places.

Effect of availability of water on organisms

In deserts the availability of water is limited and hence only special adaptations make it possible for them to live in these conditions. The vegetation of the desert looks different from that of forests. They have adapted to less water availability by having thick fleshy stems, thorns and absence of leaves.

Fig: Desert plants

Camels also have adapted to low water availability by minimising water loss. It hardly sweats thus reducing the water loss from the body and it urinates less frequently.

Fig: Camel

The distribution and productivity of plants is mainly dependent on water availability. Vegetation in tropical forests with high rainfall is different from vegetation in grassland to vegetation in coniferous forest.

The organisms living in lakes, oceans, and rivers also face water-related issues. In the case of aquatic organisms the quality of water is highly important. Salt concentration determines whether an organism can thrive or not in such a water.

Classification of organisms based on tolerance to salinity

On the basis of tolerance to salinity of water, organisms can be classified into two and they are as follows:

• Euryhaline
• Stenohaline

Euryhaline

Those organisms that are tolerant to a wide range of salinity are called euryhaline. Examples include Atlantic stingray, bull shark.

Fig: Euryhaline organisms

Stenohaline

Those organisms that are tolerant to a narrow range of salinity are called stenohaline. Examples include goldfish.

Fig: Goldfish

Light

Since the sun is the source for both the light and temperature, the availability of light on land is closely linked with that of temperature. The light is directly utilised by the plants for photosynthesis and also for flowering.

GIF: Flowering of plants

Not all plants receive the same amount of sunlight. Many plant species like shrubs and herbs growing in the regions of forests are normally adapted to photosynthesise under low light conditions as they are living under the canopy provided by the tall trees. In order to cope with low light, these plants have adapted to have large leaves to capture as much sunlight as possible.

Fig: Forest with small and large plants

Light is an important factor for animals also. Animals indirectly depend on sunlight for energy. Plants photosynthesise and produce food. Animals eat them to get energy. They also use the night-day and seasonal variations in the intensity and duration of light called photoperiod for timing their other life activities such as:

• Foraging – Searching for food.
• Reproduction – Giving birth to young ones.
• Migration - Movement of animals or birds on a seasonal basis.

Fig: Animal habits affected by light

Soil

Different types of soil can be found in different places. This is because of the process of soil development. The nature and property of the soil depends on the weathering of rocks, climates and finally how the soil is formed.

Fig: Different types of soil

The characteristics (texture, colour and composition) of soil vary. Some areas have gravel, some are in the form of aggregates or sometimes soil appears to be loose. This can determine the flow of water through the soil. When water is poured in different soil, the amount of water which retains in soil or the amount of water travels down varies. This is called percolation.

Depending on the topography, minerals present in the soil, pH of the soil, water holding capacity and percolation property of soil the vegetation at different places varies.

Fig: Factors that determine the property of soil

The sediment-characteristics of soil in the aquatic environment determines normally the type of animals that can thrive in this habitat. Benthic animals like crabs and clams are found in such areas.

Fig: Distribution of benthic animals

Practice Problems

1. Which of the following does not apply for the biotic factors?

1. The living organisms which can influence the growth and development of other living organisms in the ecosystem
2. Herbs and woody plants are the major producers of a terrestrial ecosystem
3. Carnivores are called the flexible eaters of the Animal Kingdom
4. The major examples of decomposers are bacteria, fungi etc

Solution: Those living organisms which can influence the growth and development of other living organisms in the ecosystem are called biotic factors. The organisms which can prepare their own food by utilising the energy from the sunlight (photosynthesis) or chemical energy (chemosynthesis) are called producers. Herbs and woody plants are the major producers of the terrestrial ecosystem. Those animals that can feed on both animals and plants are called omnivores. They are called the flexible eaters of the Animal Kingdom. Those organisms which feed on the dead and decayed remains of plants or animals are called decomposers. The major examples of decomposers are bacteria, fungi etc. Hence the correct option is c.

2. Depending on temperature, organisms in each region vary. Which of the following justifies this statement?

1. Camels cannot sustain low temperatures
2. Polar bears cannot stay in grasslands
3. Hornbills cannot survive in deserts
4. All the above

Solution: Temperature is the most important ecologically relevant environmental factor. The average temperature normally on land varies seasonally from cold winters to hot summers. It decreases progressively from the equator regions towards the polar regions. Depending on temperature, organisms in each region vary. For example, camels cannot sustain low temperatures in cold countries of the arctic region. Similarly polar bears cannot stay in grasslands. Zebras can not survive in extreme cold temperatures. Hornbills which stay in forest cannot survive in deserts. Hence the correct option is d.

3. Those organisms that are tolerant to a wide range of salinity are called ______________.

1. Eurythermal
2. Stenothermal
3. Euryhaline
4. Stenohaline

Solution: Based on tolerance to temperature, organisms can be classified as eurythermal and stenothermal. Those organisms that can tolerate and thrive in a wide range of temperatures are called eurythermal. Those animals that can tolerate only a narrow range of temperatures are called stenothermal. Those organisms that are tolerant to a wide range of salinity are called euryhaline. Those organisms that are tolerant to a narrow range of salinity are called stenohaline. Hence the correct option is c.

4. What is the adaptation of plants in lower canopy in order to get more sunlight?

1. Large leaves
2. Thick leaves
3. Small leaves
4. Needle leaves

Solution: Not all plants receive the same amount of sunlight. Many plant species like shrubs and herbs growing in the forest regions are adapted to photosynthesise under very low light conditions because they are constantly overshadowed by tall, canopied trees. In order to cope with low light, these plants have adapted to have large leaves to capture as much sunlight as possible. Hence the correct option is a.

Fig: Plants with large leaves under canopy

FAQs

1. Do organisms under the deep sea utilise sunlight as their energy source?

Answer: In the deep (>500m) oceans, the environment is dark and sunlight cannot reach the seafloor. The source of energy for the organisms that live deep down on the ocean floor are the dead organic matter raining down from above zones. Some organisms rely on chemicals coming out of hydrothermal vents as an energy source. They are chemoautotrophs.

Fig: Deep sea hydrothermal ecosystems

2. How does temperature affect an organism?

Answer: The temperature can affect the kinetics of enzymes. Enzymes are essential for the metabolic activity and other physiological functions of the organism. Hence the change in temperature changes the kinetic energy of enzymes and thereby changes the rate of reaction. As a result it will affect the metabolic and other physiological activities of the organism. If the enzymes can withstand a range of different temperatures, then the organism can withstand a range of temperatures.

Fig: Enzyme kinetics

3. What are the different types of detritus feeders?

Answer: There are various types of detritus feeders and the major three are, scavengers, detritivores and decomposers. Scavengers feed on the corpses and large fragments are left over by other organisms. Examples are crows, kites, vultures, hyenas, etc. Those animals that feed on freshly deposited detritus and left over by scavengers are called detritivores. They help in pulverising it. Examples are millipedes, earthworms, beetles, etc. Those microbes which help in the chemical breakdown of organic compounds are called decomposers.

Fig: Hyenas waiting for leftover meat

4. What is 10 percent law?

Answer: 10 percent law states that only 10 percent of the energy is transferred from one trophic level to the next higher trophic level. The remaining 90 percent energy is lost as heat or is used in metabolic activities. Linderman proposed the 10 percent law in 1942.

Fig: 10% law of energy transfer