Food Web: The different food chains are inter connected at various trophic level to develop a food web (Figure 39.5). For example, in grassland ecosystem, grass is consumed by the rabbit but in their absence, it may be eaten by the grazing cattle. Similarly, rat or mouse is eaten by snake but snake can be eaten by predatory birds. In contrast to food chain, food web has several distinct characteristic. (1) Food web are never straight. (2) Food web is formed due to interlinking of food chains. (3) A food web in the ecosystem brings alternate source of food. The complex food web gives better stability to the ecosystem. Most of the animals are polyphagous and they feed on more than one kind of organism. If the availability of one particular animal is decresing in the ecosystem, they start eating alternate animal. As a result, it gives chance to other animal to reproduce and grow in number and in addition, it gives chance to predator to survive.
Types of Food Chain
TYPES OF FOOD CHAIN: There are two different types of food chains; grazing food chain and detritus food chain.
Grazing food chain: In the grazing food chain, solar energy is entrapped by the plants and then biomass, in tuen eaten by the herbivorous, and these are subsequently been consumed by a variety of carnivorous. These are longer food and these food chains end at the decomposer level. Here are two typical example of this type of food chain to understand this type of food chain.
(1)
Food chain in a pond: In a pond,
floated or rooted plants and algae are responsible for performing
photosynthesis to prepare food for other member of ecosystem. They represent
producers in the food chain (Figure 39.2). Unicellular algae are consumed by
protozoan, water flies, snail, mosquito larvae and tadpoles. These small
organisms represent primary consumers. These organisms are eaten by hydra,
dragonfly larvae, giant insects and small fishes. These are secondary
consumers. Large fishes and frog fed on these organism and represent tertiary
consumers. Frog and fishes are eaten by snakes, birds and these are quaternary
consumers. Death of all these organism become the food for bacteria and fungus
to produce simple inorganic materials for reuse by the producers.
(2) Food
chain on land: A
typical land food chain is given in Figure 39.3. In land food chain, grass and
tree are the producers. Grass is eaten by rabbit and other herbivorous. They represent
the primary consumers. Rabbit is eaten by cats (secondary consumers), which
in-turn eaten by wolves (tertiary consumers). Both cat and wolves will be
consumed by tigers and other big carnivorous (quaternary consumers). Deaths of
these entire organisms become the food for bacteria and fungus to produce
simple inorganic materials for reuse by the producers.
Detritus
food chain: Unlike grazing food
chain, detritus food chain starts with the dead organic matter either from
fallen leaves or dead animal bodies. This food chain doen’t depends on solar
energy. Common example of detritus food chain is marsh land where mangrove
leaves fall into the warm, shallow water (Figure 39.4). The detritus eating
animals ex. Bacteria, fungi and protozoan act upon the dead matter of dead
leaves to covert them into simple inorganic substances. The detritivorous are
subsequently eaten by insect larvae, grass shrimp, copepods, crabs, nematodes,
bivalve mollusks, amphipods, mysids etc. In the last step, the detritus
consumers are finally eaten by fishes.
DIFFERENT TYPES OF ECOSYSTEM
Ecosystem
is an open system and material can exchange from one ecosystem to another
ecosystem. For ex. Frog move from the pond to the land and vice-versa. The
ecosystem can be classified based on size, nature and duration;
(1)
Nature : On the basis of nature, it can be natural or
artificial.
Natural Ecosystem: This ecosystem forms naturally without interference of
human. Example include are pond, river, forest, village, hill etc.
Artificial Ecosystem: This ecosystem is developed and mainted by human.
Example include are flowerbed, backyard, aquarium etc.
(2)
Duration: On the basis of duration, ecosystem can be classified
as temporary or permanent.
Temporary ecosystem: it is short lived and man made or natural. Example
include rain fed pond.
Permanent ecosystem: it is long lived and self supported natural ecosystem
for very long period. Example includes forest, river etc.
(3)
Size: Ecosystem is classified as small or large ecosystem.
(1)
Small: it
is small and also known as microecosystem. It can be temporary or permanent.
For ex. Pond, flowerpot etc
(2)
Large: it
is large in size and also known as macroecosystem. It is always permanent and
mostly natural. For ex. Ocean, river, forest and desert.
(3)
STRUCTURE OF ECOSYSTEM: Each
and every ecosystem has several components to sustain it for long duration. It
needs matter (water, oxygen, mineral, carbon dioxide), different types of
organisms and continuous recycling of energy (Figure 38.1). These requirements
are met by two important components present in ecosystem; biotic components and
abiotic components.
Biotic
Components: The living organisms
present in an ecosystem form the biotic component. They are connected through
food. In this series, few organisms are producing food whereas others are
consuling the food.
(i)
Producers: The role of producers is
to prepare food to provide nutrition to the other organisms present in the
ecosystem. There are two types of producers; photoautotrophs and chemotrophs.
Photoautotrophs:
These are green plants which can trap sun
light to form carbohydrate, simple sugar from carbon di-oxide and water. This
process is known as photosynthesis and these organisms are called as
photoautotrophs.
Chemoautotrophs: Few bacteria such as sulfur bacteria, nitrifying
bacteria, can be able to utilize free energy released from the chemical
reactions to prepare organic food with it. They are called chemoautotrophs and
the process is known as chemosynthesis.
(ii) Consumers: These are mainly the animals. They are unable
synthesize their own food and depends on producers. They utilize the oxygen
being released from the producers as well. Several consumer doesn’t get the
food from the producers but they are depended on consumers itself. As a result,
consumers are related to each other through multiple food chains. There are
many types of consumers and we will discuss in details about these consumer in
the subsequent lecture. The consumers are known as heterotrophs.
(iii) Decomposers:
These are mainly bacteria and fungi. Their
primary purpose in the ecosystem is to decompose the complex organic material
into the simple inorganic material so that it can be use for producers to
prepare food.
ABIOTIC COMPONENTS
These factors include the non-living physiochemical
factors of the environment. Abiotic factors are as follows:
(i) Inorganic
substances: Inorganic substances
like carbon, nitrogen, oxygen, water, carbon di-oxide, calcium, phosphorus and
their inorganic compounds. These are available as free form or dissolved in
water and may be adsorbed on the soil particles.
(ii) Organic
compounds: These are carbohydrates,
proteins, lipids, nuceltic acids etc. This material is present in dead organic
matter. These are broken into the simple compounds by decomposers in ecosystem
for recycling of matter.
(iii)
Climatic factors: These are factors present in the environment such as
temperature, humidity, light, wind, rainfall an atomospheric gaseous etc.
Study of specific Ecosystem: Lets take a example of
fresh water pond to understand the function of individual components.
1.
Abiotic Components: Non-living part of the pond includes: (1) water with
dissolved gases, mineral and suspended organic matter. (2) air, CO2 and O2 on
the water surface (3) sunlight.
2. Biotic
Components: The biotic constituents
include the plants, animals and microorganisms. They play different role in
ecosystem.
3.
Producers: Green plants act as producers.. As discussed
previously, they utilized the sun light, CO2 and water to prepare the food for
other organisms.
4.
Consumers: These includes crustaceans, worms, insect larvae and
fishes.
5.
Decomposers: Dead plants and animals form the organic debris in the
pond. The decomposer such as bacteria and fungi decay dead body into the simple
organic and inorganic substances.
