Trophic level- Definition, food chain, food web, pyramid, examples

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Last Updated on February 5, 2021 by Sagar Aryal

Trophic level Definition

Trophic level is the position within a food chain that is occupied by a group of organisms in an ecosystem.

  • The classification of organisms into the different food chains is based on their feeding behavior.
  • Trophic level is a step in the nutritive series of food chains which in some cases might form a complicated path called a food web.
  • The trophic level of an organism is the number of steps the organism is from the beginning of the chain.
  • The trophic level helps determine the nutritional relationship between the organism and the primary source of energy. The primary source of energy in any food chain is the sun, except in the case of some deep-sea ecosystems.
  • The concept of the trophic level was one of the first concepts to be introduced in ecology that provides a better understanding of energy flow and control within food webs.
  • The concept was introduced by Raymond Lindeman in 1942 based on the studies of August Thienemann who also coined the terms ‘producer’, ‘consumers’, and ‘reducers’.
  • The trophic levels are designated as integer values that define discrete levels as grazers or predators.
  • The trophic level of a particular organism can only be defined within a specific ecosystem and is based on its relationship with the primary energy source.
  •  Determination of trophic levels also allows the understanding of the relationship between different organisms present within the same level.
  • A trophic level is dependent on the trophic level below it as it absorbs energy from the lower trophic level and consumes it.

What is a food chain?

  • The food chain is a linear path within a food web that determines the direction of the flow of energy or biomass within an ecosystem.
  • A food chain helps determine the relationship between different organisms based on their feeding habits.
  • The food chain consists of levels, known as trophic levels, which are defined by the source of energy of the organisms belonging to the particular level.
  • The food chain is a part of the food web and is not as complicated as a food web. The chains follow a direct linear path of a particular animal.
  • The food chains of different organisms can be quantified based on the chain length. The chain length is the number of links between the organism and the base of the chain.
  • The amount of energy transferred from one link to another decrease as the length of the food chain decreases as only 10% of the total energy of a level is transferred to the next while the rest is utilized by the organism of the level.
  • The flow of energy and biomass through a food chain is essential for the survival of most species, and the removal of an element of the food chain can result in the extinction of an entire species.
  • The foundation of all food chains are producers that utilize the primary source of energy (sun or chemical reactions) to produce food that can be utilized by living beings.
  • Food chains are often prepared as a form of ecological modeling to perform various ecotoxicological studies. The food chain help trace the pathways of various environmental contaminants within an ecosystem.
  • Food chains can be broadly classified into two types based on the source of the energy; the grazing food chain and the detrital food chain.
  • The grazing food chain begins with energy and nutrient from green plants which then moves up to higher-level organisms like herbivores and carnivores or omnivores.
  • The detrital food chain begins with energy obtained from dead organic matter when consumed by decomposers which then moves to detritivores and carnivores.

What is the food web?

  • The Food web is the natural relationship between different food chains in an ecological community often represented in the form of a graphical image.
  • Food webs are often termed as consumer-resource systems as it represents the feeding habits of different organisms based on their source.
  • The concept of the food web was initially described as food cycles in 1927, which was later changed to the food web in the subsequent text.
  • Food webs are representations of real ecosystems where different living organisms are aggregated into trophic levels to generate a relationship.
  • Simplified mathematical representations are used to investigate ecological interactions to define the energy flow and balance of an ecosystem.
  • The Food web has been adapted as a conceptual tool for illustrating the feeding habits of different species in a community, their interactions, and community structure in a much-simplified way.
  • Food webs have been classified into three types by Robert Paine on the basis of different influences between species.
  • Connectedness web indicates the feeding relationship between organisms. Energy flow web represents connections that are quantified as energy flux. Functional webs illustrate the influence of population on growth rates in other populations.
  • Food webs can also be organized according to the type of ecosystem and the species present within the ecosystem.
  • Many ecologists have utilized food webs to collect data on the trophic level to determine parameters and study patterns and characteristics shared among the ecosystems.
  • Food webs are complex, and the complexity is determined by the number of species present within an ecosystem and their relationship.
  • Food webs contain distinct linear chains termed food chains which represent the direct relationship between two or more species. As the number of food chains increases, the complexity of the food web also increases.

What is the food chain energy flow?

  • Food chain energy flow is the process of transfer of energy from one point or trophic level to another in a food chain or an ecological unit.
  • The flow of energy within a food chain can be represented by an arrow where the arrowhead shows the direction of energy flow.
  • The flow of energy in a food chain is unidirectional and involves successive loss of energy as it moves from one level to another. The overall process follows the law of thermodynamics which determines the concept of energy exchange between systems.
  • It is important to understand the source of energy in an ecosystem before determining the direction of the flow. In most ecosystems, the primary source of energy is sunlight. In deep-sea ecosystems, chemical reactions might act as a source of energy.
  • Photosynthesis is the first step in the energy flow where the carbon dioxide in the environment is converted into glucose and oxygen in the presence of sunlight.
  • The energy is produced by producers (green plants and algae), which are then passed to other organisms through the food chain.
  • The energy produced by producers is termed primary production, which then moves through the food chain.
  • Secondary productivity is the biomass produced by consumers by using primary production. The consumers are present at different levels in different ecosystems, and the energy and biomass both end up on the top consumer.
  • During the transfer of energy, some energy is lost, which can be measure either by the efficiency of energy flow in terms of how much energy makes it to the next level or by the biomass.
  • The energy flow through a food chain follows the ecological rule of 10% where only 10% of the energy is transferred from one trophic level to another as the rest is utilized for metabolic processes of the organisms.

Trophic Level pyramid

  • The trophic level pyramid or ecological pyramid is the graphical structure representing the interactions in biological communities in the form of the transfer of food and energy from one trophic level to the next in a food chain.
  • The trophic pyramid is one of the three types, each of which represents the different relationship between different parameters.
  • An energy pyramid represents the flow of energy from one trophic level to another. A biomass pyramid indicates the amount of living or organic matter (biomass) present at a particular trophic level. A number pyramid represents the number of individual organisms present in different trophic levels.
  • The concept of pyramids was derived from the works of G. Evelyn Hutchinson, and Raymond Lindeman and the pyramid of numbers was the first pyramid to be developed.
  • All of these pyramids begin with the producers at the bottom, followed by other living beings at different trophic levels. The highest trophic level in the pyramid represents the top of the food chain.
  • The organisms that occupy the base of the pyramid differ in different ecosystems as in terrestrial ecosystems, green plants are present at the bottom, whereas, in aquatic ecosystems, multicellular plants and green algae occupy the level.
  • The ecological pyramid of energy is always upright as the flow of energy in an ecosystem is unidirectional, but inverted pyramids can be observed in the pyramid of biomass.
  • In ocean or pond ecosystems, the biomass of producers or phytoplanktons is lower than the biomass of zooplanktons as phytoplanktons have shorter individual lives.
  • Even though trophic level pyramids are essential to determine the efficiency of energy transfer and monitor the condition of the ecosystem, there are some limitations to these pyramids.
  • The pyramids do not represent the relationship between the ecosystem and seasons. Some species might exist at different levels that cannot be defined through the pyramids.
Trophic Level pyramid
Created with BioRender.com

Trophic Levels (with Examples)

The trophic levels in a food web begin with producers which occupy the 1st trophic level followed by various consumers and finally ending with apex predators.

A. 1st Trophic Level (Producers)

  • Producers occupy the trophic level in all food webs. These producers are responsible for the conversion of solar energy into usable energy and thus, the prime source of energy in all ecosystems.
  • Producers include green plants in terrestrial and aquatic ecosystems and green algae in deep-sea ecosystems. The photosynthetic algae in a marine ecosystem are also termed phytoplankton.
  • Both green plants and algae produce organic matter through the process of photosynthesis. In some bacteria in the deep-sea, however, the energy is obtained via chemical reactions.
  • The organisms that produce food through chemical reactions are termed chemoautotrophs and organisms that produce energy in the presence of solar energy are termed photoautotrophs.

Example- Green Plants

  • Plants are the producers of many ecosystems throughout the biosphere. Green vascular plants on land and water act as producers and are present in the trophic level 1.
  • These plants capture solar energy with the help of specialized structures called chloroplasts. The energy is then passed through different compounds to convert carbon dioxide into glucose while releasing oxygen.
  • The energy produced by the green plants is then transferred to a higher trophic level in the ecological food chain.

B. 2nd Trophic Level (Primary Consumers)

  • Primary consumers are the group of organisms that feed on producers and thus are heterotrophic. These organisms completely depend on producers like plants and phytoplankton for their energy as well as biomass.
  • These occupy the trophic level 2 of all ecosystems where 10% of the energy produced by producers is transferred. Since these organisms feed on producers, the biomass of the trophic level also increases.
  • In terrestrial ecosystems, herbivores occupy trophic level 2, which can be further divided into grazers and browsers. Grazers feed mostly on grass whereas browsers feed on tree leaves and twigs.
  • In aquatic ecosystems, zooplanktons are the primary consumers that feed on phytoplankton.

Example- Zooplankton

  • Zooplankton consists of animals that are heterotrophic and feed on phytoplankton (green algae).
  • Most of the zooplankton are microscopic, and these are greater in number than phytoplankton.
  • Common zooplanktons include zooflagellates, radiolarians, dinoflagellates, and marine micro animals. These animals feed on green plants as well as green algae for energy and nutrients.
  • In the pyramid of biomass, the trophic level 2 of primary consumers is larger than the producers as the number of zooplanktons exceeds the phytoplanktons.

C. 3rd Trophic Level (Secondary Consumers)

  • Secondary consumers are a group of animals that feed on primary consumers. These animals occupy the trophic level 3 in different ecosystems.
  • Secondary consumers include carnivores that feed on herbivores and other animals to obtain energy.
  • Secondary consumers are often termed as predators as they feed on other animals (prey) for their food.
  • Secondary consumers usually include small animals like frogs, fish, birds, and snakes but apex predators like lions and eagles might also be present in the trophic level 3.
  • In aquatic ecosystems, animals that feed on zooplankton, including smaller animals like fish to larger animals like crustaceans are present in the trophic level 3.

Example- Fish

  • Fish is a secondary consumer in an aquatic ecosystem where it feeds on zooplanktons like dinoflagellates and other micro animals.
  • Different kinds of fishes occur in different ecosystems, all of which are included in the trophic level 3. 
  • The fishes exist in a predator-prey relationship with primary consumers.

D. 4th Trophic Level (Tertiary Consumers)

  • Tertiary consumers are animals that can feed on both primary consumers as well as secondary consumers.
  • Tertiary consumers are heterotrophic are all consumers but their feeding habit is strictly carnivorous.
  • Even though tertiary consumers are present high up in ecological pyramids, these can also be feed upon by other animals and thus are not at the top of the ecosystem.
  • The tertiary consumers are present above secondary consumers in the ecological pyramid as they have less biomass as well as energy than the lower trophic levels.

Example- Owl

  • The owl is an example of the tertiary consumer in terrestrial ecosystems as it feeds on both herbivores like mice and carnivores like stoats.
  • Owls can, however, be hunted and feed upon by other animals like eagles and hawks.

E. Apex Predators

  • Apex predators are animals that are present on the top of the food chain and do not have any predators.
  • These animals are highly efficient hunters as they have a specific adaptation to the lifestyle. Some of the common apex predators in terrestrial ecosystems are vultures, eagles, lions, and tigers.
  • They can either work in groups in order to increase the chances of hunting success or alone.
  • Even though most of the apex predators in terrestrial ecosystems are vicious hunters, it is not always true in the case of all ecosystems. 
  • Sometimes, some animals can be apex predators due to the absence of their natural predators.
  • Apex predators are essential to maintain balance in the ecosystem as these animals maintain the lower trophic levels.

Example- Whale sharks

  • Whale sharks are the apex predators in marine ecosystems. These animals feed on both smaller, fishes, larger fishes as well as phytoplankton.
  • All of the whale sharks are not hunters, but these are still considered apex predators because they do not have any natural predators.
  • Because these animals feed on animals and plants of all trophic levels, they help to maintain the population of animals present in lower trophic levels. 

F. Decomposers or detritivores or transformers

  • Decomposers are organisms that feed on dead and decaying plants and animals, converting organic matter into energy and nutrients.
  • The energy and nutrients can then be taken up by plants for their effective growth.
  • Decomposers include organisms like bacteria, fungi, and some arthropods that do not form an independent trophic level but are involved in the recycling of waste material from all trophic levels.
  • These are essential in a functioning ecosystem as they prevent the loss and nutrients from the ecosystem after the death of various living beings.

Example- Bacteria

  • Bacteria are saprophytic organisms involved in the degradation of complex organic matter into smaller compounds utilized by plants.
  • There are different types of bacteria that feed on different types of organic matter, depending on the sets of enzymes produced by the bacteria.

References

  • Heath, Michael R et al. “Understanding patterns and processes in models of trophic cascades.” Ecology letters vol. 17,1 (2014): 101-14. doi:10.1111/ele.12200
  • Thompson, Patrick L et al. “Ecosystem functions across trophic levels are linked to functional and phylogenetic diversity.” PloS one vol. 10,2 e0117595. 18 Feb. 2015, doi:10.1371/journal.pone.0117595
  • Thompson RM, Hemberg M, Starzomski BM, Shurin JB. Trophic levels and trophic tangles: the prevalence of omnivory in real food webs. Ecology. 2007 Mar;88(3):612-7. doi: 10.1890/05-1454. PMID: 17503589.
  • Marczak LB, Thompson RM, Richardson JS. Meta-analysis: trophic level, habitat, and productivity shape the food web effects of resource subsidies. Ecology. 2007 Jan;88(1):140-8. doi: 10.1890/0012-9658(2007)88[140:mtlhap]2.0.co;2. PMID: 17489462.
  • Yodzis P. Energy flow and the vertical structure of real ecosystems. Oecologia. 1984 Dec;65(1):86-88. doi: 10.1007/BF00384467. PMID: 28312114.

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