5 Energy Pyramid Trophic Levels Explained
The energy pyramid trophic levels are primary producers, primary consumers, secondary consumers, tertiary consumers, and apex predators/decomposers. These levels represent the different mechanisms by which energy is transferred between organisms in an ecosystem.
In this article, the trophic levels of the energy pyramid are discussed, as outlined below;
1). Energy Pyramid Level One: Primary Producers
2). Energy Pyramid Level Two: Primary Consumers
3). Energy Pyramid Level Three: Secondary Consumers
4). Energy Pyramid Level Four: Tertiary Consumers
–Apex Predators and Decomposers
1). Energy Pyramid Level One: Primary Producers
Primary Producers typically occupy the lowest and broadest trophic level in an energy pyramid.
Otherwise referred to as ‘Autotrophs’ or ‘Autotrophic Organisms,’ the primary producers have the unique ability to manufacture (that is; to produce) their own food or energy [1].
The raw materials used by primary producers to produce energy for their use, include carbon dioxide, water and solar energy, and the process by which this energy is produced is called Photosynthesis [3].
Photosynthesis itself is basically the conversion of solar energy to chemical energy, which is a more usable form of energy for living organisms. Primary producers derive their name from the fact that they help to introduce energy into the ecosystem in a form that can be easily used by living organisms for their survival.
All primary producers are equipped with a green pigmentation called chlorophyll; which helps to trap solar energy and convert it to chemical energy (measured in units of ATP-Adenosine Tri-Phosphate).
Primary Producers share the characteristic of nutritional independence, meaning that they do not depend on any other group of living organisms for their energy and survival. Rather, all other groups are nutritionally dependent upon the primary producers.
In terms of habitat, primary producers have a versatile existence in the ecosystem. They may either be terrestrial or aquatic. Green Plants and chlorophyll-pigmented algae dominate this trophic level.
2). Energy Pyramid Level Two: Primary Consumers
All organisms above the base level of the energy pyramid (that is; above the primary producers/autotrophs) are called heterotrophs. This is because they are incapable of producing their own food (energy) from inorganic raw materials like the autotrophs.
The heterotrophs can be further divided based on the nature of their interaction with the autotrophs. This interaction may be either direct or indirect.
With the above said, trophic level 2 (from bottom to top) of the energy pyramid us occupied by organisms in the ecosystem, which interact directly with the autotrophs/primary producers.
Primary consumers may otherwise be called ‘heterotrophs’. They derive energy solely from autotrophs like plants, which they consume as food [4].
It is not difficult to observe that the energy dynamic between primary consumers and primary producers (trophic level 2 and trophic level 1) is different from that by which primary consumers derive their energy.
While the primary producers utilize and convert solar energy (in the presence of other inorganic raw materials) to chemical energy for their survival, the primary consumers simply acquire the chemical energy that is stored in autotrophic organic matter (or plant biomass), by consuming or ingesting this organic matter, for their own survival.
Because of their tendency to feed on plant biomass, the primary consumers are often referred to as herbivores. Unlike the primary producers, this group consists mostly of terrestrial organisms, although there are some aquatic herbivores.
Examples of organisms in trophic level 2 include insets like weevils and locusts, rodents like rabbits and grass-cutters, cattle, pigs, and aquatic organisms like manatees, surgeonfish, green turtles, tangs, parrotfish and blennies. These are all herbivorous plant-feeders, with a direct energy derivation pattern with respect to the primary producers at the base level.
3). Energy Pyramid Level Three: Secondary Consumers
Like the primary consumers, organisms at this trophic level of the energy pyramid are generally incapable of producing their own energy. What this obviously implies is that they are also heterotrophic, and depend on the primary producers for their energy and survival.
However, the secondary consumers differ from primary consumers in terms of how they interact with, and derive energy from the primary producers at the base of the energy pyramid.
Whereas the primary consumers (herbivores) share a direct interaction with primary producers, secondary consumers are rather indirect in their energy-transfer relationship with the primary producers.
Secondary consumers feed on the primary consumers for survival [2]. The energy which they derive from this feeding activity is the same chemical energy which was converted utilized, and stored by the primary producers, and which was subsequently acquired by the primary consumers.
The energy-dynamic between the three trophic levels (1, 2 and 3) which has been described in the paragraph above, is what makes up the food chain and food web in the ecosystem. Primary producers introduce chemical energy into the ecosystem by capturing and converting solar energy, and this chemical energy is transferred through feeding, from the primary producers, to all other organic groups.
A term which is alternatively used to describe the secondary consumers which occupy trophic level 3, is ‘Carnivores’ (or carnivorous organisms). Ideally, the carnivores depend only on herbivores for their food.
The habitat of secondary consumers/carnivores, ranges from terrestrial to aquatic. This group is fairly diverse, and includes mammals, insects, reptiles, birds and fish. Some common examples include piranhas, foxes, spiders, snakes and seals.
4). Energy Pyramid Level Four: Tertiary Consumers
Tertiary consumers derive their energy in a similar manner to the secondary consumers.
This is because tertiary consumers are also carnivorous in their feeding habits, and depend on other heterotrophs (organisms that depend on autotrophs for energy) to survive.
However, the tertiary consumers occupy trophic level four (the highest basic level of the energy pyramid) above the primary and secondary consumers, because they are capable of deriving energy by feeding on the secondary consumers (as well as the primary consumers).
Ideally, organisms in trophic level 4 (tertiary consumers) of the energy pyramid, do not directly interact with tropic level 1. This is because they are not herbivores and do not ingest plant biomass. Rather, this group comprises of the more complex and developed carnivores like jaguars, pumas, whales, and crocodiles. Carnivorous birds like hawks belong to this category, although they are often categorized as secondary consumers as well.
In some cases, organisms which are classified under the tertiary consumer (trophic level 4) group may feed on both plant and animal biomass. Such cases include bears, although this phenomenon is in the minority.
Apex Predators and Decomposers
In some energy pyramid models, a fifth energy level is identified. This level is occupied by the ‘apex predators’ as they are called.
The apex predators include organisms which are capable of deriving energy from (that is; of feeding upon) organisms from all trophic levels of the energy pyramid.
Basically, the apex predator category is designed to accommodate plant-and-animal feeders, also called ‘omnivores’. The classic example of these organisms is humans.
Another important group which does not fall into any particular trophic level of the energy pyramid is known as the decomposers. As the name implies, these organisms play the crucial role of energy recycling in the ecosystem.
Decomposers recycle chemical energy in the ecosystem by breaking down plant and animal biomass. These organisms survive by using the energy that is stored in the remains of dead organisms. They also return some of this energy to the ecosystem in the form of soil nutrients and atmospheric gases.
The nutrients and gases are subsequently used by plants in photosynthesis, thereby repeating the energy circulation dynamics that makes up the energy pyramid.
Conclusion
There are four main trophic levels of the ecosystem. Collectively, they signify the various pathways through which energy is transmitted through an ecosystem, across the various groups of organisms.
The base level of the pyramid (trophic level 1) is occupied by primary producers; which are also called autotrophs. They include chlorophyll-pigmented algae and green plants. These organisms are called autotrophs because they are capable of producing their own food using solar energy and other inorganic raw materials.
Organisms at the trophic level 2, depend directly on autotrophs for energy. This means that they feed primarily on plants as a source of nutrition. These organisms are referred to as primary consumers or herbivores, and include herbivorous rodents like rabbits; insects like grasshoppers, and ruminants like goats.
Trophic level 3 (in order from bottom to top) is occupied by secondary consumers. These are organisms that feed on the herbivores (primary consumers) in order to gain energy. They include snakes, foxes and seals.
There is another group of organisms which are called tertiary consumers. These organisms occupy trophic level 4, and include highly-developed carnivores like crocodiles, that feed on both herbivores (primary consumers) and other carnivores (secondary consumers).
It is important to note that the energy which is transferred across the trophic levels of the energy pyramid is the same solar energy that is initially trapped by plants at the base of the pyramid. Other important organic groups which do not fall into any of the basic trophic levels include apex predators and decomposers.
References
1). Bailey, R. (2020). “What Is an Autotroph? Definition and Examples.” Available at: https://www.thoughtco.com/what-is-an-autotroph-definition-and-examples-4797321. (Accessed 5 February 2022).
2). Daniel, F. (2020). “What are Secondary Consumers? Examples in Food Chain.” Available at: https://www.jotscroll.com/what-are-secondary-consumers-examples-in-food-chain. (Accessed 5 February 2022).
3). Gough, C. M. (2011). “Terrestrial Primary Production: Fuel for Life.” Nature Education Knowledge 3(10):28. Available at: https://www.nature.com/scitable/knowledge/library/terrestrial-primary-production-fuel-for-life-17567411/. (Accessed 5 February 2022).
4). Hunt KA, Jennings RM, Inskeep WP, Carlson RP (2018). “Multiscale analysis of autotroph-heterotroph interactions in a high-temperature microbial community”. PLoS Comput Biol 14(9): e1006431. Available at: https://doi.org/10.1371/journal.pcbi.1006431. (Accessed 5 February 2022).
