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Trophic Level Definition
A trophic level refers to a position in an ecological pyramid, food chain, or food web. . Each trophic level is occupied by a group of organisms having similar feeding mode. The term trophic is derived from the Greek word ‘trophē’, meaning ‘food’.
What is Trophic Level?
A group of organisms with similar feeding modes occupy a specific position in an ecological pyramid or food chain. In ecology, this position is referred to as trophic level. Organisms in an ecosystem are grouped into nutritional (trophic) levels in a particular hierarchy known as a food chain.
The trophic level represents the flow of energy via food and the feeding relationships among organisms. It is represented in a series or succession. In an ecosystem, the biomass or energy flow is represented by an ecological pyramid. Both the food chain and ecological pyramid start with primary producers and are represented as trophic level 1.
Organisms that obtain nutrition by feeding on primary producers are grouped into the next trophic group. Then, the succeeding trophic levels each have a group of organisms that feed on the life forms at the trophic level before them.
If the succession occurs in one way it is called the food chain, and if it occurs in more intricate paths it is called the food web. In other words, a food web has many interlinked food chains. Rather than a direct food chain, most ecosystems have a complex food web structure.
Trophic Level Categories
Autotrophs and heterotrophs are the two major categories in trophic levels. Autotrophs are producers of an ecosystem because they prepare their food (organic matter) from inorganic matter, and do not need to depend on other life forms for the same. Heterotrophs are the consumers of an ecosystem as they cannot produce their food and hence depend on other organisms for organic matter (food).
They can be further classified as primary, secondary, tertiary consumers, and so on. Herbivores or plant-eating organisms occupy the place of primary consumers. The secondary consumers obtain organic matter by consuming primary consumers Secondary consumers are consumed by tertiary consumers and so on. Reducers/ Scavengers are the final groups that consume dead organic matter. Detritivores and decomposers are included in these categories.
Structure of Trophic Level
The division of biomass between different trophic levels is referred to as trophic structure. Mainly biomass of the producers control this structure and affects the transfer efficiency by essentially providing energy and nutrient input. Predators prevent the overpopulation of herbivores by predation and hence help primary producers.
Predators serve as biological by helping the suppression of lower trophic levels. Primary productivity is also promoted by predators by intraspecific competition. Thus, primary producers and predators are very important factors for regulatory control.
Trophic Level Pyramid
Trophic levels in an ecosystem are graphically represented as an energy pyramid. Sun is the ultimate source of energy, and it passes through various trophic levels while transferring through the ecosystem. Only 10% of the total energy in a trophic level is transferred to the next level. There are higher amounts of energy and biomass at the lowest trophic level i.e., bottom of the pyramid, so to support energy requirements of the subsequent trophic levels.
A trophic level pyramid is a representation of plants and animals in a certain ecosystem depending upon their eating habits. It is used to depict the ecological pyramid. It is in the shape of a pyramid to indicate that organisms at the bottom trophic level can make their food i.e., producers, by utilizing the available resources from the environment representing the base.
As we move upwards in the pyramid, it tapers towards the peak indicating the diminishing energy level. Thus, the pyramid shape depicts the biomass and energy in each trophic level. The amount of organic matter in an organism is the biomass. The base has the largest amount of biomass which diminishes as it moves to the subsequent trophic levels, and is lowest at the apex.
The trophic levels in an ecosystem can be most commonly represented by such pyramidal structures. However, there are also cases wherein the pyramid is inverted. This occurs when the combined weight of consumers is higher than the combined weight of producers.
The ecological pyramid is also referred to as Energy Pyramid as it also represents the energy flow through various trophic levels. The lowest trophic level has the highest amount of energy. Energy flow also follows the same trend as the biomass and diminishes as we go from bottom to top in an ecological pyramid.
Trophic Level Examples
Level 1: Producers
Primary producers are found in the tropic level 1 at the base of the ecological pyramid. It is occupied by plants and algae. The characteristic feature of primary producers is that they can synthesize their food from inorganic matter. E.g., they can synthesize organic matter via photosynthesis.
Photosynthesis is a process wherein energy-rich carbohydrate i.e., glucose is synthesized by utilizing carbon dioxide, water, and light energy. Oxygen is produced as a by-product in this reaction. The following is the photosynthesis equation:
6CO2 + 12H2O + energy = C6H12O6 + 6O2 + 6H2O
The photosynthetic pigments i.e., chlorophyll found inside the chloroplasts of plants and algae can absorb light energy. Hence chloroplasts are also known as light-harvesting organelles.
Level 2: Primary Consumers
Primary consumers occupy the next trophic level in an ecological pyramid or a food chain or an ecological pyramid i.e., trophic level 2. Organisms of this trophic level consume primary producers and they are known as herbivores. They have some characteristic features 9anatomican and physiological) to get adapted to plant diet. E.g., they have typical oral features like a wide flat mouth that helps them to grind tree bark and foliage.
Typically, they have oral features that help them to rasp or grind plant materials. They also have specialized digestive flora of cellulose-digesting protozoans that can digest cellulose which is found abundant in plant cell walls. Examples of herbivores: Cattles, goats, and horses.
Level 3: Secondary Consumers
Animals that consume primary consumers i.e., predators occupy the tropic level 3 of an ecological pyramid or a food chain. These secondary consumers hunt and kill their prey to feed on them. Their characteristic feature (anatomical and physiological) is adapted for animal diet.
Predators (carnivores) have advanced senses that they need to hunt down their prey. To not get noticed by prey, they have characteristics of camouflaging or mimicking. To grab hold of their prey and cut it open, they have strong jaws, fangs, and sharp claws. Even preys have evolutionary features to escape predation.
They have developed defense strategies and counter adaptations such as alarm calls, spines, mimicry, thanatosis, chemicals, camouflage, and warning coloration. Some of the animals with predator-prey relationships include bear and fish, fox and rabbit, lion and zebra, and spiders and flies. Killer whales are an example of apex predators because no animals can prey on them.
Dolphins, seals, and fishers are the marine prey of killer whales. However, not all predators exclusively eat meat, some of them feed on plants as well. Omnivores are animals that feed on both plants and animals. Omnivores may feed on algae, bacteria, and fungi as well.
Omnivores do not have specialized features for processing food. Examples of omnivores include Pigs, most bears, squirrels, chimpanzees, rodents, etc. Most humans are omnivores however some of them prefer only a plant-based diet. Carnivorous plans can also be included in this group.
Along with photosynthesis, these plants can use predation as another means of obtaining food. photosynthesis. Certain marine organisms that consume zooplankton are also considered secondary consumers e.g., lobsters and crabs.
Other Trophic Levels
Tertiary consumers are the organism that consumes secondary consumers and are included on trophic level 4. Quaternary consumers are the ones that consume tertiary consumers and are included in trophic level 5.
Decomposers
Decomposers such as detritivores that feed upon dead plants and animals, occupy the last of the trophic level. Detritivores consume their food after fragmenting it. Examples of detritivores include dung flies, slugs, millipedes, worms, and woodlice. Other decomposers include fungi and bacteria that consume readily available nutrients at a molecular level e.g., substrates derived from rotting organisms and already digested material.
Decomposers need their nutrients to be in their simplest form for consumption as opposed to other consumers that digest their food after consuming them. Decomposers also include parasites ha rely on the host for organic material but may or may not kill them. Decomposers occupy the top of the ecological pyramid. Fungi are considered to be most common decomposers. They have enzymes to break down complex molecules of the dead organism.
Even bacteria have the enzyme to decompose complex organic molecules into simpler forms. After decomposition, the detritivores scavenge the decomposing organic matter or detritus. Decomposers play a vital role in an ecosystem as they decompose complex organic matter of deceased organisms, a part of which returns to earth in the form of geochemical components.
Planktons
Planktons photosynthetic or heterotrophic organisms living on aquatic habitats. They are microscopic organisms. In an ecological pyramid or food chain, they are distributed in different trophic levels. Phytoplanktons are capable of photosynthesis and hence considered producers. Zooplanktons or heterotrophic planktons consume other planktons and hence are classified as consumers.
Biomass Transfer Efficiency
In an ecological pyramid, the maximum amount of biomass is found at the base of the pyramid or tropic level 1 (producers) because it is lost progressively as we move up in the pyramid. The amount of biomass of the producers is a limiting factor to the biomass of the primary consumers as primary consumers depend on producers for food.
Similarly, the biomass of secondary consumers depends on the amount of biomass of primary consumers. Thus in an ecosystem, usually the ecological pyramid has the widest first trophic level and the narrowest topmost trophic level. Ecosystem stability is maintained due to the distribution of biomass.
In the case of an inverted pyramid, wherein the consumers’ population outgrows the available primary producers, there is a chance that the ecosystem could fail.
Significance of Trophic Level
To understand the interrelationships between organisms and the ecological processes it is essential to monitor the trophic level. The stability of an ecosystem can be measured by keeping track of the magnitude of herbivory, predation, and decomposition.
Trophic Level Citations
- The interactions of Trichoderma at multiple trophic levels: inter-kingdom communication. Microbiol Res . 2020 Nov;240:126552.
- Trophic transfer of microplastics in aquatic ecosystems: Identifying critical research needs. Integr Environ Assess Manag . 2017 May;13(3):505-509.
- Importance of accurate trophic level determination by nitrogen isotope of amino acids for trophic magnification studies: A review. Environ Pollut . 2018 Jul;238:677-690.
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