TERRESTRIAL FOOD CHAIN: LINKS AND EXAMPLE - BIOLOGY - 2025

The terrestrial food chain is the process of transfer of nutrients and energy that occurs between the different species that inhabit a terrestrial ecosystem. In this, each link feeds on the one that precedes it and in turn is food for the next.

The sequence of the bonds begins with the producer organisms, which have the ability to create organic compounds from other inorganics. Then there is the group of consumers, who obtain their energy from organic elements.

Food chain. Source: pixabay.com

The decomposing organisms fulfill the function of closing the cycle. Thus, matter is returned to the environment.

In the terrestrial food chain, if one of the links disappears, the subsequent ones would be left without food. In addition, the species that are in the immediately previous level, of the disappeared trophic level, experience an overpopulation. This is because the predators that consume them are no longer present in the ecosystem.

Example of a simple food chain / Photo retrieved from: e-ducativa.catedu.es.

At each trophic level there is an accumulated energy, which is transferred to the next link. However, approximately 10% of this is lost in the passage of each level. Thus, from the energy point of view, a third-order consumer organism is less efficient than a primary one.

Links

The terrestrial food chain is structured in links, where each one obtains its energy from the immediately previous level. In the case of producer organisms, their energy source comes from sunlight or chemical reactions.

- Primary producers

This group constitutes the base of the trophic chain and is made up of autotrophic organisms. These have the ability to make their own organic matter, such as lipids, carbohydrates and proteins, starting from inorganic nutrients that they take from the air or soil.

To carry out this process, these living beings use the sun's rays or the chemical reactions of some minerals as an energy source. In general, producers can be classified into phototrophs and chemotrophs:

Phototrophs

Within this grouping are plants and some green algae. These have specialized structures, the chloroplasts, where the process of photosynthesis occurs. These organelles, which are found at the cellular level, are surrounded by membranes.

In the internal part of this structure there are various organelles, such as ribosomes, as well as lipids and starch granules. They also have thylakoids, which are sacs in whose membranes the photosynthetic pigments are located. Some of these are chlorophyll and carotenoids.

Phases of photosynthesis

The photosynthetic process occurs in two phases, the light and the dark. In the light stage, carbon dioxide, which is taken from the environment through the stomata, and water molecules intervene. Light energy, absorbed by chlorophyll, acts on these compounds.

This excites the external electrons of the chloroplast, which in turn transmits the excitation to adjacent molecules. This produces a kind of electric current, which is used in the synthesis of ATP and NADPH.

Both compounds are needed in the next stage, the dark phase. In this, energy, in the form of ATP and NADPH, is used to synthesize sugars. These will be the basis for the production of starch and sucrose. Another important by-product of this process is oxygen, which is released into the atmosphere.

Chemotrophs

This group of organisms synthesize their food through redox, where an inorganic compound, such as sulfur, is reduced. From this process the energy that is used in respiration is obtained, among other metabolic processes.

Some representatives of this type of primary producers are nitrogen bacteria and colorless sulfur bacteria.

- Consumers

Heterotrophic living beings make up the group of consumers. These are not capable of producing their own food, so they need to obtain energy from the consumption of organic matter from other living beings.

Primary consumers

These mainly feed on the producing organisms. Thus, herbivores, as they are also known, can consume different parts of plants, such as flowers, fruits, stem, leaves, roots or seeds.

In addition, there is a group of animals, among which are the bees, which feed on substances made by plant species, such as the nectar of flowers. Some examples of this food link are the rabbit, the hare, the panda, the deer, the cow and the sheep.

Secondary consumers

Second order consumers are those animals that feed on herbivores or primary consumers. To this group belong the carnivores, whose bodies are anatomically and physiologically adapted for a meat-based diet.

Some secondary consumers are the fox, the wolf, the tiger, the hyena, the cougar, the weasel, the bobcat and the lynx.

Tertiary consumers

This link in the food chain is made up of animals that usually include second-order consuming species in their diet. Birds of prey, such as the eagle or the vulture, are examples of this trophic group.

- Decomposers

Some experts consider decomposing organisms as a nutritional level, while others place them within the consumer group. In any case, these are responsible for degrading organic waste and transforming it into substances assimilated by plants.

- Energy transfer between trophic links

Energy flow through the food chain occurs in an upward and linear fashion. However, when moving from one level to another there are losses. Thus, a quaternary consumer receives less energy than a tertiary one.

At the moment that energy enters a trophic level, much of it is stored as biomass, thus forming part of the body of the organism. This energy is available for the next trophic level, since it will be consumed by the organisms that comprise it.

In general, the stored energy is not fully transmitted to the next link. This partial transfer restricts the length of terrestrial food chains. Thus, after the third trophic level, the energy that flows is relatively low, which prevents the effective maintenance of populations.

Causes

One of the reasons for this inefficiency in energy transmission is heat loss. This occurs mainly in respiration and in other processes of metabolizing organic matter.

Furthermore, a good part of the organisms that make up a link are not eaten by the predators of the next level. These can die without being consumed. However, dead matter is food for decomposers, so that energy is not lost.

Likewise, consumers rarely eat all the food they have hunted. This causes the loss of a good part of the organic mass and therefore of energy.

Example

In the different terrestrial ecosystems there is a wide diversity of food chains. One of these begins with the annual plant belonging to the Brassicaceae family, the wild arugula (Eruca vesicaria).

This primary producer is consumed by the common rabbit (Oryctolagus cuniculus), which devours its succulent leaves, thus constituting a primary consumer.

This herbivorous animal is part of the diet of the red fox (Vulpes vulpes), which, within the terrestrial food chain, is located at the secondary consumer level. As for the last trophic link, there is the falcon, a member of the Falconidae family. This bird of prey chases and hunts the fox, to consume its meat.

When some of these living things die, decomposing organisms, such as bacteria and fungi, act. Thus, they degrade corpses and excreta products, and transform them into elements assimilated by plants.

References

1. Wikipedia (2019). Food chain. Recovered from en.wikipedia.org.
2. Juan José Ibáñez (2011). Ecosystems: Food Networks, Energy Networks, Food Chains and Population Pyramids. Recovered from madrimasd.org.
3. Hui, D. (2012) Food Web: Concept and Applications. Nature Education Knowledge. Recovered from nature.com.
4. National geographic (2019). Food chain. Recovered from nationalgeographic.org.
5. Encyclopaedia Britannica (2019). Food chaing. Recovered from britannica.com.