Food chain and food web

1. Food chain
Definition:
The transfer of food energy from the producers, through a series of organisms
(herbivores to carnivores to decomposers) with repeated eating and being eaten, is known
as food chain.
Components of a Food Chain:
 Producers - 'base' of the food chain
 Herbivores - feed on producers
 Omnivores - feed on both plants and animals
 Carnivores - feed on herbivores, omnivores, & other carnivores
o lst level carnivore - feeds on herbivores
o 2nd level carnivore - feeds on 1st level carnivores
 Decomposers
o the 'final' consumer group
o use energy available in dead plants and animals
o transform organic material into inorganic material
 Food chains are of three types:
(a) Grazing or Predator food chain.
(b) Parasitic food chain.
(c) Saprophytic or detritus food chain.
(a) Grazing or Predator Food Chain:
 This food chain starts fromgreen plants (producers), passes through the herbivore
(primary consumers) and ends with carnivore (secondary or tertiary consumers).

2.  Autotroph→ Herbivore→ Primary Carnivore →Secondary Carnivore→ Tertiary
Carnivore → Decomposer etc.
 E.g. of aquatic ecosystem
Phytoplankton →Zooplankton→ Fish→ Hawk
 E.g. of grassland ecosystem
Grass→Rabbit→Fox→Wolf→Tiger
 Grass→ Grasshopper→ Frog→Snake→Hawk
(b) Parasitic food chain:
In this type of food chain either the producer or the consumer is parasitized.
So the food passes to the smaller organism.
The energy transfer through this kind of food chain is not significant.
 Producer→ Herbivores→ Parasite→ Hyper parasites
 Trees→ Fruit eating birds→ Lice and bugs→ Bacteria and fungi
(c) Saprophytic or Detritus Food chain:
 This type of food chain starts from dead organic matter of decaying animals and
plant bodies to the micro-organisms and then to detritus feeding organism and to
other predators.
 The food chain depends mainly on the entry of organic matter produced in another
system.
 The organism of the food chain includes algae, bacteria, fungi, protozoa, insects,
nematodes etc.

3. Significance of Food Chains and Food webs
1. They help in maintaining the ecological balance.
2. They help in understanding the feeding relations among organisms.
3. Energy flow and nutrient cycling take place through them.
4. The movement of sometoxic substances (like DDT) in the ecosystem, sprayed
to kill the pests and insects, through the various trophic levels, their accumulation
at the highest trophic level, etc. can be studied(bio magnification).
Food web
Food web can be defined as, "a network of food chains which are interconnected at various
tropic levels, so as to forma number of feeding connections amongstdifferentorganisms
of a biotic community".
It is also known as consumer-resource system.
All the food chains are interconnected and overlapping within an ecosystem and they
make up a food web.
Important facts
• A node represents an individual species, or a group of related species or different
stages of a single species.
• A link connects two nodes. Arrows represent links, and always go from prey to
predator.
• The lowest tropic level are called basal species.
• The highest tropic level are called top predators.

4. • Movement of nutrients is cyclic but of energy is unidirectional and non-cyclic.
Types of food web representation
Different food webs
• Soil food web
• Aquatic food web
• Food web in forest
• Food web of grassland
• Food web in terrestrial and aquatic ecosystem
• These food webs simply indicate a
feeding relationship.
TOPOLOGICAL
WEBS
• Bio-energetic webs, or flow webs,
include information on the strengthof
the feeding interaction.
FLOW WEBS
• In interactionthe arrows show how
one group influences another.
INTERACTION
WEB

5. Significance of food web

6.  Food webs are important tools in understanding that plants are the foundation of
all ecosystems and food chains.
 Food webs aid in the understanding of natural selection.
 Food webs are helpful in explaining how disruptions in populations due to over-
hunting, poaching, global warming and habitat destruction result in food
scarcities leading to extinction
Trophic level
Definition:
The levels of a food chain (food pyramid) is called Trophic levels. The trophic
level of an organism is the level it holds in a food pyramid.
 The sun is thesourceof all the energy in foodchains. Green plants, usually the first
level of any food chain, absorb some of the Sun’s light energy to make their own
food by photosynthesis. Green plants (autotrophs) are therefore known as
‘Producers’ in a food chain.
 The second level of the food chains is called the Primary Consumer. These
consume the green plants. Animals in this group are usually herbivores. Examples
include insects, sheep, caterpillars and even cows.
 The third in the chain are Secondary Consumers. Theseusually eat up the primary
consumers and other animal matter. They are commonly called carnivores and
examples include lions, snakes and cats.
 The fourthlevel is called TertiaryConsumers.Theseareanimals that eat secondary
consumers.
 Quaternary Consumers eat tertiary consumers.
 At the top of the levels are Predators.

7.  Predators feed on preys.
 A prey is an animal that predators hunt to kill and feed on.
 Predators include owls, snakes, wild cats, crocodiles and sharks. Humans can
also be called predators.
 When any organism dies, detrivores (like vultures, worms and crabs) eat
them up.
 The rest are broken down by decomposers (mostly bacteria and fungi), and
the exchange of energy continues.
 Decomposers start the cycle again.
Energy flow
The Sun is the principal source of energy input to biological systems. The Earth
receives 2 main types of energy from the Sun: light (solar)and heat.

8. Photosynthetic plants and some bacteria can trap light energy and convertit
into chemical energy.
Non-cyclical nature of energy flow
Heterotrophic organisms obtain their energy by eating plants or animals that have
eaten plants. So all organisms, directly or indirectly, get their energy from the Sun.
The energy is passed from one organism to another in a food chain but, unlike water
and elements such as carbon and nitrogen, energy does not return in a cycle.
Energy give out by organisms is lost to the environment.
Energy is lostat each level in the food chain, as in the examples below.
 Energy lost through the process of respiration (as heat)
 Energy used up for movement (to search for food, find a mate, escape from
predators…).
 Warm-blood animals (birds and mammals) maintain a standard blood
temperature – they lose heat to the environment.
 Warm-blood animals lose heat energy in faeces and urine.
 Some of the material in the organism being eaten is not usedby the consumer,
for example a locust does not eat the roots of maize, and some of the parts eaten
are not digestible.
On average, about 90% of the energy is lost at each level in a food chain.
This means that in long food chains, very little of the energy entering the chain
through the producer is available to the top carnivore.
So there tend to be small numbers of top carnivores.
The food chain below shows how energy reduces through the chain. It is based on
maize obtaining 100 units of energy.
maize ---> locust ---> lizard ---> snake
100 units 10 units 1 unit 0.1 unit

9. On shorter food chains, less energy is lost.