ECOSYSTEM
INTRODUCTION
Ecosystem is the smallest
structural and functional unit of nature or environment. It is a self
regulatory and self sustaining unit.
Ecosystem may be large
or small. A single drop of water may be an ecosystem.
Ecosystem may be
temporary or permanent.
TYPES OF ECOSYSTEM
An ecosystem may be
natural or artificial.
Natural ecosystem is
divided into two basic categories –
Terrestrial ecosystem
: E.g., forest, grassland, tree, desert ecosystem.
Aquatic ecosystem
: Aquatic ecosystem is again of two types:
Lentic ecosystem : E.g., Stagnant fresh
water, lake, pond, swamp.
Lotic ecosystem : Running freshwater
ecosystem. E.g., river.
Artificial ecosystem : These are man made
ecosystem. E.g., cropland, gardens etc.
On the basis of size,
types of ecosystem are :-
Mega ecosystem –Ocean/Sea
Macroecosystem –Forest
Microecosystem –Pond
Nanoecosystem –Drop of water
COMPONENTS OF ECOSYSTEM
An ecosystem is composed of two components –
Biotic component
Abiotic component
BIOTIC COMPONENTS
Biotic component is made up of many
different inter
dependent population, e.g., plants, animals, microbes, etc.
Types of biotic
component are - producer, consumer& decomposer
PRODUCERS
All the autotrophs of an
ecosystem are called producers. The green plants are the main producers.
Producers are generally chlorophyll bearing organisms which produce their own
food by the process of photosynthesis, in which producers absorb solar energy
and convert it into chemical energy. So producers are also called transducers
or converters. E.g., yellow green algae, algal protist etc.
Energy enters into the
ecosystem through the producers.
The solar energy is the only ultimate source of energy in the
ecosystem. This energy is available for the remaining living organisms.
Other examples of
producers are –
Chemoautotrophs : Iron bacteria, sulphur
bacteria, nitrifying bacteria.
Phytoplankton : In an aquatic ecosystem,
rooting plants called phytoplankton are the major autotrophs.
Phytoplanktons may produce as much food as produced by the larger
shrubs and trees in unit area.
CONSUMER
All the heterotrophs of
the ecosystem are known as consumers. It includes micro-organisms. These
directly
(on herbivores) or indirectly (on carnivores) depend on the producers for food.
Types of consumer are :
macroconsumers and micro-consumers.
Macroconsumers /
Phagotrophs or holozoic digest their food inside the
body of organism i.e. first ingestion then digestion.
Macro-consumers are of
following type :
Primary consumer : Such living
organisms which obtain food directly from producers or plants are known as
primary consumers.
E.g., Herbivores of ecosystem, cow, grazing cattle, rabbit.
They are also known as secondary producers as they synthesize
complex materials in the cells by the digestion of food which is obtained from
the plant.
Secondary consumers or
primary carnivores:
Those animals which feed upon primary consumers and obtain food.
Those carnivores which kill and eat the herbivores are called predators. E.g.,
dog, cat, snake. In aquatic system, whale is a secondary consumer. It is an
example of a filter feeder because it feeds on plankton.
The organisms which
completely depend on dead animals are not examples of predators but they all
are scavengers or detritivores. E.g., Vulture, crow, fox.
Vulture is a scavenger
not predator because it never kills any animal. Vulture is also
a decomposer. In vulture, the break down of the food material takes
place inside the body and then released into the soil in the form of waste
material and minerals.
All predators are
carnivores but all carnivores are not predators.
Plant parasites are
known as primary consumers while animals parasites (E. coli
bacteria, Entamoeba histolytica, liver fluke, tapeworm) are known as secondary
consumers.
All the insectivorous
plants play the double role i.e. producer as well secondary
consumer because they synthesize their own food through photosynthesis
and they eat insects simultaneously.
Man and peacock are
omnivores.
Organisms which use milk
or curd are known as secondary consumers.
Top (tertiary) consumers
: Those
animals which kill other animals and eat them, but are not killed & eaten
by other animals in nature are called tertiary consumers. E.g., Lion, man,
peacock.
Micro-consumers/Decomposers
or Scavengers/Osmotrophs are those living organisms which decompose the dead body of
producers and consumers.
The main
decomposers in ecosystem are bacteria and fungi.
Decomposers play a
significant role in mineral cycle.
DECOMPOSITION
Decomposers are
responsible for converting complex organic material of dead minerals or plants
into simpler organic matter through the process of decomposition and release
mineral substances into the soil where these are reused by the producers, so
that soil is considered as the best resource of minerals.
The upper layer of the
soil is the main site for decomposition process in the ecosystem.
The process of
decomposition involves several processes. These processes can be categorised
as:
1. fragmentation of detritus
2. leaching
3. catabolism
4. humification
5. mineralization
Detritivores (e.g., earthworm)
breakdown detritus into smaller particles (called fragmentation).
By the process of leaching,
water soluble inorganic nutrients' go down into the soil horizon and get precipitated
as unavailable salts.
In bacteria and fungi,
process of decomposition completely takes place outside the body. They
carry out catabolism and release extracellular enzymes from their body on dead
remains and decompose it into simpler organic substances and
then absorb it. So these are called as osmotrophs (absorptive).
In the process of
decomposition, some nutrients get tied up with the biomass of microbes and
become temporarily unavailable to other organisms. Such incorporation of
nutrient in living microbes (bacteria & fungi) is called nutrient
immobilisation.
Humification and
mineralization occur during decomposition in the soil. Humification leads to
formation of humus which is highly resistant to microbial action &
undergoes extremely slow decomposition. Humus serves as a reservoir of
nutrients.
Mineralization results in the
release of inorganic substances (e.g., CO2, H2O) and
variable nutrients (NH4+, Ca++, Mg++,
K+ etc.) in the soil.
Decomposition is largely
an oxygen requiring process.
Factors affecting
decomposition –
Temperature and soil
moisture are important and regulate decomposition through their effects on the
activates of soil microbes.
Warm and moist
environment favour decomposition whereas low temperature and anaerobiosis inhibit
decomposition.
