Concept of Trophic level
in an ecosystem (Greek word ‘ trophic’ = to
nourishing or feeding)
1.
A trophic level refers to the
position or place of an organism in the food chain.
2. The
number of trophic levels is equal to the number of steps in the food chain.
3. The green plants or grasses occupying the first trophic level (T1) and they
are called producers.
4. The
energy produced by the producers or autotrophs is consumed by primary
consumers (Herbivores; the plant eaters in the form of food, and they
occupies the second
trophic level (T2).
5. Primary
consumers are eaten by primary carnivores, which occupy the third trophic level (T3). They
are also called secondary consumers.
6. Primary
Carnivores (Secondary consumers) are eaten by the top carnivores, which occupy
the fourth trophic level (T4). They are
called the tertiary consumers or secondary carnivores.
7. Some
organisms which eat both plants and animals are called as omnivores (for
example Man, Crow etc). Such organisms may occupy more than one trophic level
in the food chain. Trophic level of any food chain of any ecosystem never exceeds
more than T4.
Food chain
A food chain refers to the
order of events in an ecosystem, where one living organism eats another
organism, and later that organism is consumed by another. Simply, Food chain is a linear sequence
of eaters being eaten.
A food chain is a linear
network of links, it starting from producer organisms and ending at apex
predator species such as killer whale, detritivores (like earthworms or woodlice),
or decomposer species such as fungi or bacteria.
In any food chain, energy
flows from producers to primary consumers, then from primary consumers to
secondary consumers, and finally secondary consumers to tertiary consumers.
Hence, it shows linear network links. Each level of a food chain represents a
different trophic level (T).
For example, a food chain might start with a green plant/
grass as the producer (T1), which is eaten by a grasshopper, the
primary consumer (T2). The grasshopper might then be the prey of a
secondary consumer (T3) such as a frog, which itself may be eaten by
a tertiary consumer (T4) such as a snake.
Generally, there are two types of food chain,
(1) Grazing food chain and (2) Detritus food chain.
1. Grazing food chain
The grazing food chain starts
with producers like green plants or grass, and later goes to grazing herbivores
to carnivores.
Grazing food chain is directly dependent on the flow of solar
energy. Solar energy serves as the primary source of
energy in the grazing food chain. For Example;
|
Producer T1 |
Primary consumer ( Herbivores) T2 |
Secondary consumer (first Carnivores)
T3 |
Tertiary consumer ( Second carnivores)
T4 |
Apex Predator |
|
|
|
Blue bird |
|
Owl |
Types of Grazing Food
Chain
There are mainly two types of grazing food chains
and they are as follows:
- a. Predator food chain – It starts with herbivores and goes from smaller to larger predators. Here, one animal consumes another animal. The animal that is being eaten is known as the prey and the animal that is eating the prey is known as the predator. The size of predator increases at each trophic level in the food chain. Predator of first level is smaller than the second level. For example:
- b. Parasitic
food chain – Here, the plants and animals in a grazing
food chain are infected by parasites. It begins with the herbivores but
food energy passes from larger to smaller organisms. Here, larger animals are the host and a
smaller animal which fulfills their nutritional requirement from the host
are called parasite. For example;
2. Detritus food chain:
This type of food chain begins
with dead organic matter i.e. Detritus. It is
derived from the dead plants, animals and their excreta. The energy from the dead organic
matter is transferred through detritus consumers (detritivores) to small carnivores
and then to large (top) carnivores with repeated eating and being eaten
respectively. This is called the detritus food chain. For example
Food Web
In Nature food chains are not isolated but are
interconnected with one another. A different type of food chains interact with
each other.This interlocking pattern of several food chains is called as food
web.
The inter-locking pattern of a number of
food chain form a web like arrangement called food web.
In a food chain one organism serves as food source of more than
one organism. Hence one type of food chain gets interlinked with other and
forms a network or web pattern. For example; a grass, is the food source of a
rabbit or a mouse or grasshopper. The
mouse or rabbit in turn may be eaten directly by a hawk or by a snake and the
snake may be directly eaten by hawks. Similarly, The Grasshopper in turn may be
eaten directly by a frog or by a Lizard and the Lizard may be directly eaten by
hawks or by snake. This trophic relationship
between the organisms of an ecosystem forms a complicated network. Hence, this interlocking
pattern of food chains is the food web.
.
Significance of food
web
· Food webs are very important in maintaining
the stability of an ecosystem. For example the deleterious growth of grasses is controlled by
the herbivores. When one type of herbivore becomes extinct, the other type of
herbivores increases in number and control the vegetation.
Difference between food chains and
food web.
In a food chain, many
trophic levels are linked. While in food web many food chains are linked.
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