The study of cellular Biology Topics is essential to understanding the workings of all living organisms.
How many Trophic Levels are there? Trophic level Diagram – Ecological Pyramids
A food chain represents the flow of food (or energy) in a given set of organisms or living beings. The various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels. In fact, in a food chain, each step representing an organism forms a trophic level. In most simple terms, ‘trophic level’ means ‘feeding level’ of the organism.
- The plants are producers (or autotrophs) and constitute the first trophic level. They fix up the sun’s energy and make it available for consumers (or heterotrophs).
- Herbivores (which feed upon plants) constitute the second trophic level.
- Carnivores (that feed upon herbivores) constitute the third trophic level.
- Large carnivores or Top carnivores (which feed upon small carnivores), constitute the fourth trophic level.
The various trophic levels in a food chain can be represented diagrammatically as shown in Figure.
Herbivores are called primary consumers, small carnivores are called secondary consumers whereas top carnivores or large carnivores are called tertiary consumers. So, we can draw another diagram to represent various trophic levels by using the terms producers, primary consumers, secondary consumers and tertiary consumers as shown in Figure.
Please note that both, secondary consumers and tertiary consumers are carnivores, the only difference being that secondary consumers are small carnivores (though we usually do not write the word small), whereas tertiary consumers are large carnivores which are usually called top carnivores. Please note that the diagram shown in Figure is tapering upwards because as we go up towards higher trophic levels, the number of organisms in them decreases gradually.
The simplest food chain that we have already studied is :
Grass → Deer → Lion
Now, this food chain involves three trophic levels. Grass (being producer) represents the 1st trophic level. Deer (being herbivore) represents the 2nd trophic level, and lion (being carnivore) represents the third trophic level.
We have also studied another food chain operating in the grassland, which is :
Grass → Insect → Frog → Bird
In this food chain, grass represents the 1st trophic level; insects represent the 2nd trophic level; frog represents the 3rd trophic level, whereas birds represent 4th trophic level. This is shown more clearly in Figure.
We will now consider some of the food chains involving man (human beings). Now, when man eats plants (or plant products), then the food chain involves only producer and consumer:
This food chain has only two trophic levels. Plants being the first trophic level and the man representing second trophic level. But in the case of man who also eats meat (of animals like goat), the food chain involves producer and two consumers, the primary consumer and the secondary consumer :
This food chain involving man has three trophic levels. Plants represent 1st trophic level, goat represents 2nd trophic level whereas man represents the 3rd trophic level.
The trophic levels in a food chain can also be represented by pyramid of numbers. Thus, if we count the number of species (or organisms) living at each trophic level in a food chain, then we can represent the food chain by a pyramid of numbers. A pyramid of numbers showing the various trophic levels in the grassland food chain : Plants → Mice → Snakes → Hawks is shown in Figure. The base of this pyramid is formed by producers (plants) and the top of this pyramid is formed by the highest order consumers (or top carnivores).
Please note that the same ecosystem may be supporting many different pyramids of organisms, each starting with plants at the base but ending in a different organism at the top. Another point to be noted is that there is a greater number of organisms at the lower trophic levels of an ecosystem (the greatest number being at the producer level). As we go to higher and higher trophic levels, the number of organisms in each trophic level goes on decreasing (as shown in Figure).
Effect of Man’s Activities on the Ecosystem
Man or for that matter, any other living organism must interact properly with the rest of the ecosystem because he is an integral part of that ecosystem. Some of the man’s activities like hunting of various animals disrupt the food chains in which these animals normally take part. This disruption of one food chain affects the numerous other food chains operating in the food web. The shortening of food chains due to man’s activities like hunting leads to an imbalance in the functioning of an ecosystem and ultimately in the functioning of the whole biosphere. The effect of man’s activities on the functioning of an ecosystem will become clear from the following examples.
The formation of Sahara Desert is an example of the ill effect of man’s activities on the delicately
balanced ecosystem. When the Romans started capturing lions, the population of lions in the forest was reduced to a large extent. Lion is a predator which kills the herbivorous animals like deer, sheep, goat, buffalo, etc. Now, since the population of predator lion decreased, there was no one to kill the herbivorous animals. Due to this the population of herbivorous animals increased rapidly.
The large population of these herbivorous animals ate up all the vegetation (plant materials) in that region, turning the lush-green forests into vast desert called Sahara Desert. Our own Rajasthan Desert was formed as a result of overgrazing of vegetation by progressively increasing tribes of herbivorous animals which occurred due to the reduction in the predator population of lions because of excessive hunting and capturing.
Let us take the example of Grass → Deer → Lion food chain to study the effect of man’s activities on the ecosystem. A natural ecosystem is a delicately balanced system. If the man does not disturb this ecosystem, then the organisms like grass, deer and lion in a forest keep a natural balance which benefits them all and gives us a healthy environment. We will now discuss the effect of removing all the three organisms from this food chain, one at a time.
(i) If All the Lions are Removed
If all the lions in a forest are removed by killing or capturing, then there will be no predator control over the population of deer. Due to this the population of deer will increase greatly. Deer eat grass. So, an increase in deer population will lead to excessive grazing of grass. The density of producers like grass will be very much reduced. Overgrazing may even eliminate the grass and other green plants completely and turn the lush-green forest into a desert area having no vegetation at all.
(ii) If All the Deer are Removed
Deer is a food (or prey) for lion. Now, if somehow, all the deer population from a forest is removed, then there will not be sufficient food for the lions. Some of the lions will die because of starvation and hence the population of lions will decrease. The decrease in population of lions will disturb other food chains in which lions operate. The hungry lions of the forest can come out of the forest in search of food and may even kill domestic animals or human beings for obtaining food. If the lion and deer are operating in other food chains of the food web, the removal of deer population and the subsequent reduction in lion population will disturb the balance of ecosystem.
(iii) If All the Producers are Removed
If all the producers like grass and other plants are removed, then no deer or lion (or any other organism) will be able to exist. This is because the food and energy necessary for sustaining life is derived from the producer organisms-like grass, plants and their products.
From the above examples we conclude that if we kill all the organisms in one trophic level, it will cause too much damage to the environment. So, we cannot remove all the organisms of a trophic level without causing any damage to the ecosystem. The impact of removing all the organisms of a trophic level will be different for different trophic levels (as explained in the above given examples). We will now answer some questions based on trophic levels.
Example Problem 1.
Which of the following belong to the same trophic level ?
Grass; Hawk; Rabbit; Frog; Deer
Here, grass is a producer, hawk is a top carnivore, rabbit is a herbivore, frog is a carnivore and deer is a herbivore. Since rabbit and deer are both herbivores, so they belong to the same trophic level (2nd trophic level).
Example Problem 2.
Which of the following belong to the same trophic level ?
Frog; Grasshopper; Grass; Snake; Algae
Here, frog is a carnivore, grasshopper is a herbivore, grass is a producer, snake is a top carnivore, and algae is producer. Since grass and algae are both producers, so they belong to the same trophic level (1st trophic level).