7Ecosystems-Concept
of an ecosystem-Structure and function of an ecosystem-producers, consumers and
decomposers-Energy flow in the ecosystem-Ecological succession –Food
chains-food webs and ecological pyramids
Ecosystems
are functional units consisting of living things in a given area, non-living
chemical and physical factors of their environment, linked together through
nutrient cycle and energy flow. The chemical components of the ecosystem move
in defined cycles–biogeochemical cycles. Within the ecosphere, biological
systems frequently regulate the rate of movement of cycling of the chemicals.Ecosystems
can be permanent or temporary.
Structural aspects
1)
Inorganic aspects – C, N, CO2, H2O.
2) Organic compounds – Protein, Carbohydrates, Lipids – link abiotic
to biotic aspects.
3) Climatic regimes – Temperature, Moisture, Light & Topography.
4) Producers – Plants.
5) Macro consumers – Phagotrophs – Large animals.
6)
Micro consumers – Saprotrophs, absorbers – fungi.
Functional aspects
1)
Energy cycles.
2) Food chains.
3) Diversity-interlinkages between organisms.
4) Nutrient cycles-biogeochemical cycles.
5)
Evolution.
Since
each ecosystem has a non-living and a living part that are linked to each
other, one needs to look around us and observe this closely. This is an
important aspect that is a vital part of our lives.
The
non-living components of an ecosystem are the amount of water, the various
inorganic substances and organic compounds, and climatic conditions such as
rainfall and temperature, which depend on geographical conditions and location
which is also related to the amount of sunlight. The living organisms in an
ecosystem are inseparable from their habitat.
The
living component of plant life ranges from extremely small bacteria, which live
in air, water and soil, algae which live in fresh and salt water, to the
terrestrial plants which range from grasses and herbs that grow after the
monsoon every year, to the giant long-lived trees of the forest. The plants
convert energy from sunlight into organic matter for their growth. They thus
function as producers in the ecosystem. The living component of the animal
world ranges from microscopic animals, to small insects and the larger animals
such as fish, amphibia, reptiles, birds and mammals. Man is just one of the 1.8
million species of plants and animals that inhabit the earth.
Producers, consumers and decomposers
Every
living organism is in some way dependent on other organisms. Plants are food
for herbivorous animals which are in turn food for carnivorous animals. Thus
there are different tropic levels in the ecosystem. Some organisms such as
fungi live only on dead material and inorganic matter.
Plants
are the ‘producers’ in the ecosystem as they manufacture their food by using
energy from the sun. In the forest these form communities of plant life. In the
sea these include tiny algal forms to large seaweed.
The
herbivorous animals are primary consumers as they live on the producers. In a
forest, these are the insects, amphibia, reptiles, birds and mammals. The
herbivorous animals include for example hare, deer and elephants that live on
plant life. They graze on grass or feed on the foliage from trees. In
grasslands, there are herbivores such as the blackbuck that feed on grass. In
the semiarid areas, there are species such as the chinkara or Indian gazelle.
In the sea, there are small fish that live on algae and other plants.
At a
higher tropic level, there are carnivorous animals, or secondary consumers,
which live on herbivorous animals. In our forests, the carnivorous animals are
tigers, leopards, jackals, foxes and small wild cats. In the sea, carnivorous
fish live on other fish and marine animals. Animals that live in the sea range
in size from microscopic forms to giant mammals such as the whale.
Decomposers or detrivores
Decomposers
or detrivores are a group of organisms consisting of small animals like worms,
insects, bacteria and fungi, which break down dead organic material into
smaller particles and finally into simpler substances that are used by plants
as nutrition. Decomposition thus is a vital function in nature, as without
this, all the nutrients would be tied up in dead matter and no new life could
be produced.
Most
ecosystems are highly complex and consist of an extremely large number of
individuals of a wide variety of species. In the species-rich tropical
ecosystems (such as in our country), only a few species are very common, while
most species have relatively few individuals. Some species of plants and
animals are extremely rare and may occur only at a few locations. These are
said to be ‘endemic’ to these areas.
When
human activities alter the balance in these ecosystems, the “perturbation”
leads to the disappearance of these uncommon species. When this happens to an
endemic species that is not widely distributed, it becomes extinct for all
time.
Energy flow
Energy efficiency is lost
at successive trophic level and non cyclic
The
energy cycle is based on the flow of energy through the ecosystem. Energy from
sunlight is converted by plants themselves into growing new plant material
which includes leaves, flowers, fruit, branches, trunks and roots of plants.
Since plants can grow by converting the sun’s energy directly into their
tissues, they are known as producers in the ecosystem. The plants are used by
herbivorous animals as food, which gives them energy. A large part of this
energy is used up for day to day functions of these animals such as breathing,
digesting food, supporting growth of tissues, maintaining blood flow and body
temperature. Energy is also used for activities such as looking for food,
finding shelter, breeding and bringing up young ones.
Carnivores
in turn depend on herbivorous animals on which they feed. Thus the different
plant and animal species are linked to one another through food chains. Each
food chain has three or four links. However as each plant or animal can be
linked to several other plants or animals through many different linkages,
these inter-linked chains can be depicted as a complex food web. This is thus
called the ‘web of life’ that shows that there are thousands of
interrelationships in nature.
The
energy in the ecosystem can be depicted in the form of a food pyramid or energy
pyramid. The food pyramid has a large base of plants called ‘producers’. The
pyramid has a narrower middle section that depicts the number and biomass of
herbivorous animals, which are called ‘first order consumers’. The apex depicts
the small biomass of carnivorous animals called ‘second order consumer’. Man is
one of the animals at the apex of the pyramid. Thus to support mankind, there
must be a large base of herbivorous animals and an even greater quantity of
plant material.
When plants and animals die, this material is returned to the soil
after being broken down into simpler substances by decomposers such as insects,
worms, bacteria and fungi so that plants can absorb the nutrients through their
roots. Animals excrete waste products after digesting food, which goes back to
the soil. This links the energy cycle to the Nitrogen cycle.
Ecological Succession
Ecological
succession is a process through which ecosystems tend to change over a period
of time. Succession can be related to seasonal environmental changes, which
create changes in the community of plants and animals living in the ecosystem.
Other successional events may take much longer periods of time extending to
several decades. If a forest is cleared, it is initially colonized by a certain
group of species of plants and animals, which gradually change through an
orderly process of community development. One can predict that an openedup area
will gradually be converted into a grassland, a shrubland and finally a
woodland and a forest if permitted to do so without human interference. There
is a tendency for succession to produce a more or less stable state at the end
of the successional stages. Developmental stages in the ecosystem thus consist
of a pioneer stage, a series of changes known as serel stages, and finally a
climax stage. The successive stages are related to the way in which energy
flows through the biological system. The most frequent example of successional
changes occur in a pond ecosystem where it fluctuates from a dry terrestrial
habitat to the early colonisation stage by small aquatic species after the
monsoon, which gradually passes through to a mature aquatic ecosystem, and then
reverts back to its dry stage in summer where its aquatic life remains dormant.
Food chain food web and ecological pyramids
The
transfer of energy from the source in plants through a series of organisms by
eating and being eaten constitutes food chains. At each transfer, a large
proportion of energy is lost in the form of heat. These food chains are not
isolated sequences, but are interconnected with each other. This interlocking
pattern is known as the food web. Each step of the food web is called a trophic
level. Hence green plants occupy the first level, herbivores the second level,
carnivores the third level and secondary carnivores the fourth level. These
trophic levels together form the ecological pyramid.
Food chains
The most
obvious aspect of nature is that energy must pass from one living organism to
another. When herbivorous animals feed on plants, energy is transferred from
plants to animals. In an ecosystem, some of the animals feed on other living
organisms, while some feed on dead organic matter. The latter form the
‘detritus’ food chain. At each linkage in the chain, a major part of the energy
from the food is lost for daily activities. Each chain usually has only four to
five such links. However a single species may be linked to a large number of
species.
Definition: The
transfer of energy from plants through a series of organisms with repeated
eating and being eaten
Food web
In an
ecosystem there are a very large number of interlinked chains. This forms a
food web. If the linkages in the chains that make up the web of life are
disrupted due to human activities that lead to the loss or extinction of
species, the web breaks down.
Ecological pyramids
In an
ecosystem, green plants – the producers, utilize energy directly from sunlight
and convert it into matter. A large number of these organisms form the most
basic, or first ‘trophic level’ of the food pyramid. The herbivorous animals
that eat plants are at the second trophic level and are called primary
consumers. The predators that feed on them form the third trophic level and are
known as secondary consumers. Only a few animals form the third trophic level
consisting of carnivores at the apex of the food pyramid. This is how energy is
used by living creatures and flows through the ecosystem from its base to the
apex. Much of the energy is used up in activities of each living organism.
No comments:
Post a Comment