FOOD
CHAIN & FOOD WEB
Food Chain
·
For example, plants are eaten by
insects, insects are eaten by frogs, these frogs are eaten by fish, and fishes
are eaten by human beings. [Plant > insect > frog > fish > human]
This sequence is known as Food chain.
What
is Trophic Level?
·
Each step in the food chain is called
a “Trophic level”.
·
In this food chain: Plant > Insect
> Frog > Fish > Human= five steps.
·
The trophic level to which an organism
belongs, indicates how far it is away from plants in the food chain.
·
Green plants (producers) = trophic
level I
·
Herbivores (primary consumers) =
trophic level II
·
Carnivores (secondary consumers) =
trophic level III
·
Top carnivores (tertiary consumers) =
trophic level IV
·
Herbivores (deer, cow etc.) are always
@ second trophic level.
·
Higher trophic levels are made up of
carnivores.
·
An organism cannot always be assigned
to one specific trophic level.
·
E.g. man (omnivore), so he is both a
herbivore (@2nd trophic level) and as a carnivore he can be (@>2nd trophic
level)
Types
of Food Chains
|
Type
of Food Chain
|
|
|
Food Chain
|
Description
|
|
Grazing
|
Starts with green plants.
Ex: Grass> grasshoppers>
birds> hawks.
|
|
Parasitic
|
Also starts with green plants but
here smaller organisms depending on larger organism. e.g. Grass> cow>
lice.
|
|
Detritus* /saprophytic
|
Starts with dead plant/animal/ waste
material> decomposers.
|
|
*Detrius = dry leaves, dead plant,
animal remains, dead skin cells, other organic waste (urine, excreta).
|
|
Ecological
Pyramids
·
We already know about the food chain:
[Grass
–> Grasshoppers –>birds –>Hawk]
·
Each step or level is known as Trophic
level.
·
If we draw these trophic levels in a
verticle fashion, a pyramid is created. This pyramid is known as Ecological
pyramid.
·
The Autotrophs (green plants) = base
of the pyramid
·
The top carnivores (lion tigers) = tip
(apex) of this pyramid.
Types
of Pyramids
·
Pyramid of numbers
·
Pyramid of biomass
·
Pyramid of energy or productivity
Food
Web
·
Food Chain: Grass> grasshopper
>frog > fish > man
·
Food chain assume the isolated linear line.
But in real life, frog could be eating other insects apart from grasshopper.
Fish could be eating smaller fishes apart from frog. So there exists an
interconnected Network of (Food Chain + Food Chain + Food chain…).
·
This interconnected network of food
chains = food web.
Why
is Food web important?
·
Suppose in a jungle, the deer species
is wiped out due to some human poaching/ diseases / natural disaster.
·
Then its predators (lion, tiger) can
feed on other animals such as fox, wolf, crane, peacock etc. until deer
population grows again.
·
Thus, food web= help living organism
survive in case of minor or major setbacks in their food chain.
·
Food web=provides stability to the
ecosystem.
Energy
Flow in the Ecosystem
·
When energy is passed from one tropic
level to next trophic level, some part of energy is wasted. So energy declines
as we move up in the chain/ web / pyramid.
·
Because some energy is wasted as body
heat.
·
No herbivore (deer, cow) can entirely
digest and absorb the plant nutrients.
·
Some energy is wasted while capturing
the prey. (Ex: Tiger chasing a deer.)
·
Some energy remains trapped e.g. Tiger
only eats the flash of a deer. He doesn’t eat the skin, hair, bone and teeth of
a deer.
·
So the energy stored in the skin,
hair, bone and teeth of a deer =not moved up in the food chain.
·
However this energy is later utilized
when scavenger (hyena) comes into picture. Because Hyena’s stomach acid is so
powerful, it can digest the skin, hair, bone, teeth and other remnants of a
deer corpse.
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