Contents
One of the most pressing Biology Topics of our time is the conservation of endangered species and habitats.
Types, Characteristics, Significance of Food Chain – Biological Magnification
The transfer of food energy from producers to a series of consumers through the different trophic levels in an ecosystem is known as the food chain.
Or
The process in which food energy passes from producer to consumer in a linear sequence of eating and being eaten is known as the food chain (Odum, 1966).
Formation of Food-chain
In an ecosystem, green plants act as primary producers who trap solar energy and transfer it to chemical or potential energy in organic compounds like carbohydrates, proteins, and fats. When a herbivorous animal eats a plant and these organic compounds are oxidized, the energy liberated is just equal to the amount of energy used in synthesizing substances, but some of the energy is lost and not used. If this animal, in turn, is eaten by another animal (secondary consumer) along with the transfer of energy from the primary consumer to the secondary consumer, a further decrease of useful energy occurs. At each transfer, about 80-90% of potential energy is liberated as heat.
Characteristics of Food-chain
- Green plants are the producers of the food chain.
- The producer lies at the base of each food chain.
- The nature of the food chain is very much complicated.
- In a food chain, from base to apex, the number decreases, but the size increases.
- The number of steps in a food chain is always restricted.
- In the same environment, numbers of food chains are always interlinked and their disciplinary arrangements construct a food web.
- The herbivores are called primary consumers; first-level carnivores, secondary consumers; second-level carnivores, tertiary consumers and third level carnivores, quaternary consumers; and so on.
- The shorter the food chain, the more efficient it is. A large number of steps results in a waste of energy and makes the chain unstable.
- There is a unidirectional flow of energy from the sun to producers and then to a series of consumers of various types. Thus, the food chain is always straight and proceeds in a progressing straight line.
- Plants and animals depend successively on one another from the limbs of a food chain.
Types of Food-chain
There are three types of food chains:
- Grazing food- chain or predator food chain
- Detritus food-chain
- Parasitic food-chain
1. Grazing Food-chain
The grazing food chain starts from green plants (producers), passes through plant-eating animals (herbivores), and ends in carnivores. The producers (green plants) trap the solar energy from the sun and store it in the food. Green plants occupy the producer level (first trophic level), plant eaters form the level of primary consumers (second trophic level), the carnivores that feed on the herbivores, occupy the secondary consumers level (third trophic level) and the secondary carnivores occupy the tertiary consumer level (fourth trophic level). Thus a typical food chain is formed.
Characteristics of Grazing Food Chain
- They are directly dependent upon solar radiation as the primary source of energy and the producers synthesize their plant biomass by the process of photosynthesis. Producers form the first trophic level.
- Herbivores eat upon the producers and form the second trophic level.
- Herbivores are in turn eaten by different categories of carnivores forming the higher trophic levels.
- Grazing food chains are longer food chains and they always end at the decomposer level.
In an ecosystem, the producer-consumer arrangement represents a trophic structure where each food level is called a trophic level.
2. Detritus Food-chain or Saprophytic Food-chain
Detritus means the organic debris from decomposing plants and animals. In this type of food chain, the dead organic matter (e.g., fallen leave, roots, animal dung) are acted upon by decomposers (bacteria, fungi, etc.). Such decomposed organic matter is again eaten by some aquatic animals, e.g., insect larvae, nematodes, etc.
Such aquatic small animals that directly feed on organic matter are called detrivores or detritus consumers. Detrivores are again consumed by smaller carnivores (small fish), which in turn are preyed upon by larger carnivores (large fish). Another example of the detritus food chain can be explained by the fallen leaves of a mangrove tree. When the leaves of a mangrove tree fall into the water, the parts of the leaves are eaten by smaller organisms like insect larvae, crabs, etc. Later those organisms are eaten by carnivorous small fishes. Finally, these small fishes are eaten by larger fishes or fish-eating birds.
Characteristics of Detritus Food Chain
- The primary source of energy is dead organic matter called ‘detritus’ which are fallen leaves, plant parts, or dead animal bodies.
- Primary consumers are ‘detrivores’ including the protozoans, bacteria, fungi, etc., which feed upon the detritus saprophytically.
- Detrivores are in turn eaten by secondary consumers such as insect larvae, nematodes, etc.
- Detritus food chains are generally shorter than grazing food chains.
- In nature, detritus food chains are indispensable as the dead organic matter of the grazing food chain is acted upon by the detrivores to recycle the inorganic elements into the ecosystem.
Detritus Food Chain in a Table Form:
| Detritus | Detrivores | Detrivores Consumers | Small Carnivores | Large Carnivores |
| Mangrove, Fallen Leaves, and Dead Bodies. | Fungi, Bacteria, and Protozoans. | Insect Larvae, Certain Crustaceans, Molluscs, and Fishes. | Minnows, Small game fish, etc. | Large Fish, Fish-eating Birds. |
Differences between Grazing and Detritus Food Chains:
| Characters | Grazing Food Chain | Detritus Food Chain |
| Primary Source of Energy | Solar Radiations | Detritus. |
| First Trophic Level | All Herbivores | Detrivores (a mixed group in terms of trophic levels and may be herbivores, omnivores, and primary carnivores). |
| Size | Long-sized chains | Small-sized chains |
3. Parasitic Food-chain
It goes from larger (host) to smaller (parasite) animals.
Several Examples of Some Food-chain
A. Grassland Food-chain
B. Forest Food-chain
C. Aquatic Food-chain
D. Predator Food-chain
E. Saprophytic Food-chain
Significance of Food-chains
Food chain studies help in,
- Understanding the feeding relationships and the interaction between organisms in any ecosystem.
- Comprehend the energy flow mechanism and matter circulation in ecosystems.
- Understand the movement of toxic substances and the problem of ‘Biological magnification’ in the ecosystem.
- Analyze the biological diversity in an ecosystem.
Biological Magnification
Certain harmful substances, usually ones not found in nature but introduced by man, may get into plants and animals. These poisonous substances may not be broken down in the body or excreted easily, efficiently, and quickly. Instead, they accumulate in the tissues, and as the living organism eats more, the concentration of these substances increases and that pass from one trophic level to the next. Since man is an omnivore and has access to all the trophic levels for food, he gets the toxic substances located on the top of the food chain and also gets the poison into their body and accumulates in large concentrations. This phenomenon is called biological magnification.
Food-web
In nature, food chain relationships are not isolated. They are very complex, as one organism may form the food source of many organisms. Thus, instead of a simple linear food chain, there is a web-like structure formed by these interlinked food chains. Such an interconnected matrix of food chains is called the ‘food web’.
A food web can be defined as, “a network of food chains which are interconnected at various trophic levels, so as to form a number of feeding connections amongst different organisms of a biotic community”.
Food webs are indispensable in ecosystems as they allow an organism to obtain its food from more than one type of organism of the lower trophic level. Generally, a food web operates according to the taste and food preferences of the organism, yet the availability of food sources and other compulsions are equally important. For example, tigers normally do not eat fish or crabs, but Sunderbans are forced to feed on them in the absence of their natural prey.
Various types of food chains are interconnected with one another by different species and this interlocking pattern operating in an ecosystem, is called food-web. Various types of food chains are observed among the bio-community of any ecosystem. In nature, independent and linear food chains are very rare. In an ecosystem, many food chains operate simultaneously. All the food chains are connected with one another to form a network. Different trophic levels form a knot of a food chain. Producers always lie at the base of any food chain and the existence of other trophic levels depends on the producers. Consumers may be primary, secondary, tertiary, etc. In a food web, the relationship between eating and being eaten does not remain constant as the food web is composed of many food chains at a time. These food chains combine’ together to form a network that indicates the pattern of energy or nutrient flow throughout an ecosystem.
For example, a field mouse may be consumed by a wild cat, a snake, or a hawk. Again, wild cats may eat a number of other herbivores. A wolf or jackal can consume both rabbit and deer. The food web accurately represents all the various food chains that actually exist in an ecosystem. The food web also contributes as an important tool for investigating the ecological interactions that define energy flows and the relationship between predator and prey.
Difference between the Food Chain and the Food Web:
| Food Chain | Food Web |
| 1. The food chain is a single straight pathway by which the food energy circulates in the ecosystem. | 1. The food web contains, a number of interconnected food chains by which the food energy passes in the ecosystem. |
| 2. In the food chain, only the members of one trophic level compete to obtain the same type of food. | 2. In the food web, there is competition among the members of the different species. |
| 3. Here, there is no adaptability and competitiveness among the organisms. | 3. Here, there is increased adaptability and competitiveness among the organisms. |
| 4. The presence of separate or isolated food chains adds to the instability of the ecosystem. | 4. The presence of a food web increases the stability of the ecosystem. |
Grassland Food-web in Ecosystem
- Grass → Grasshopper → Hawk
- Grass → Grasshopper → Lizard → Hawk
- Grass → Rabbit → Wolf
- Grass → Mouse → Hawk
- Grass → Mouse → Snake → Hawk