1Ecosystem:
An ecosystem is a community of living organisms (plants and animals) sharing an environment.
OR
An ecosystem is complex set relationship among living resources, habitats and residents of an
area. It includes animals, plants, trees, fishes, microorganisms, water, soil and people.
The largest ecosystems are called biomes.
A BIOME is a major ecosystem spread over a wide geographic area, and characterized by
certain types of flora and fauna.
Types of ecosystem
There are basically two types of ecosystems;
1) Terrestrial ecosystem.
2) Aquatic ecosystem.
A) Terrestrial ecosystems
Terrestrial ecosystems are found everywhere apart from water bodies. They are broadly
classified into:
a) The Forest Ecosystem
b) The Desert Ecosystem
c) The Grassland Ecosystem
d) The Mountain Ecosystem
a) The Forest Ecosystem
These are the ecosystems where abundance of flora (plants) is seen and they have a large number
of organisms living in relatively small areas. Therefore, the density of life in forest ecosystems is
very high. Any small change in the ecosystem can affect the whole balance and collapse the
ecosystem. You can see wonderful diversity in the fauna of these ecosystems too. They occupy
nearly 40% of the land. In India , the forest occupies roughly 19% of the total land area. They are
again divided into few types.
1. Tropical evergreen forest: Tropical forests which receive an average rainfall of 80 to 400
inches in a year. These forests are marked by dense vegetation comprising of tall trees with
different levels. Each level gives shelter to different kinds of animals.
2. Tropical deciduous forest: Dense bushes and shrubs rule here along with broad levels of
trees. This type of forests is found in many parts of the world and large variety of flora and fauna
are found here.
3. Temperate evergreen forest: Temperate evergreen forests are characterized by their hardy
trees. Trees need to withstand sandy, rocky, and basically poor quality soil, occasional fires,
droughts and cold weather. These forests are generally dominated by pine trees, but also support
many other kinds of vegetation.These found in areas receiving more than 200 cm of rainfall and
having a temperature of 15 °C to 30 °C. They occupy about seven per cent of the Earth's land
surface and harbour more than half of the world’s plants and animals.
4. Temperate deciduous forest: This forest is found in the moist temperate regions with
sufficient rainfall (75-126 cm). Winters and summers are well defined and dominated by broad –
leaved hard wood trees (oak ,hickory) that lose their foliage annually during winter. They are
found in areas where warm moist summers alternate with mild winters. These are the first
biomes to be converted into agriculture use.
5. Taiga: Situated just south of the arctic regions, Taiga is distinguished by evergreen conifers.
While the temperature is subzero for almost six months, the rest of the year it is buzzing with
insects and migratory birds. Taiga is the world's largest land biome, and makes up 29% of the
world's forest cover; the largest areas are located in Russia and Canada. The taiga is the terrestrial
biome with the lowest annual average temperatures after the tundra and permanent ice caps.
Extreme winter minimums in the northern taiga are typically lower than those of the tundra.
6. Tundra is a biome where the tree growth is hindered by low temperatures and short growing
seasons. In tundra, the vegetation is composed of dwarf shrubs, sedges, grasses, mosses and
lichens Scattered trees grow in some tundra.
Functions of forest ecosystem:
1. Watershed protection
2. Atmospheric regulations
3. Soil erosion control
4. Wind erosion control
5. Noise pollution control
II) The Desert Ecosystem
Desert ecosystems are found in regions receiving an annual rainfall of less than 25cm. They
occupy around 17 percent of all land on the planet. Due to very high temperature, intense
sunlight and low water availability, flora and fauna are very poorly developed and scarce.
Vegetation is mainly bushes, shrubs, few grasses and rarely trees. Leaves and stems of these
plants are modified to conserve water. The best known desert plants are the succulents like spiny
leaved cacti. Animal life includes insects, reptiles, birds, camels all of whom are adapted to the
xeric (desert) conditions.
Types of desert ecosystem
1.Sand desert 2.Rock desert 3.Cold desert 4. Stony desert 5. Plateau desert 6. Mountain desert.
Functions of desert ecosystem
1. Solar energy resource
2. Mineral resource
III) The Grassland Ecosystem
Grasslands are found in both temperate and tropical regions of the world but the ecosystems are
slightly varying. This area mainly comprises of grasses with very little amount of shrubs and
trees. Main vegetation is grasses, legumes and plants belonging to composite family. Many
grazing animals, herbivores and insectivores are found in grasslands.
Two main types of grasslands ecosystems are:
1. Savanna: These tropical grasslands are seasonally dry with few individual trees. They
support large number of grazers and predators.
2. Prairies: This is temperate grassland. It is completely devoid of trees and large shrubs.
Prairies can be categorized as tall grass, mixed grass and short grass prairie.
Functions of grassland ecosystems.
1. These are breading areas
2. These provide food.
3. Human habitat
IV) The Mountain Ecosystem
Mountain lands provide a scattered but diverse array of habitats in which a large range of plants
and animals are found. At higher altitudes harsh environmental conditions generally prevail, and
only treeless alpine vegetation is found. The animals living here have thick fur coats for
prevention from cold and hibernate in winter months. Lower slopes commonly are covered by
coniferous forests.
B) Aquatic Ecosystems
An aquatic ecosystem is an ecosystem located in a body of water. It comprises aquatic fauna,
flora and the properties of water too. There are three types of aquatic ecosystems
1. Marine
2. Freshwater.
3. Wetlands
1.) The Marine Ecosystem
Marine ecosystems are the largest ecosystems with coverage of nearly 71% of the Earth's surface
and containing 97% of the planet's water. The water in Marine ecosystems has salts and minerals
dissolved in them in high amounts. Different divisions of marine ecosystems are:
1. Oceanic: The relatively shallow part of the ocean that lies over the continental shelf. It is the
edge of a continent that lies under the ocean.
2. Profundal: Bottom or deep water.
3. Benthic Bottom substrates.
4. Inter-tidal: The area between high and low tides.
5.Estuaries, Salt marshes
6.Coral reefs
7. Hydrothermal vents- chemosynthetic bacteria form the food base.
2.) Wetlands: Places where the soil is saturated or inundated for at least some time. These
ecosystems are home to amphibians, reptiles and almost 41% of world’s fish species. Faster
moving turbulent water typically contains greater concentrations of dissolved oxygen, which
supports greater biodiversity than the slow moving water of pools.
3) The Freshwater Ecosystem: In contrast to the Marine ecosystem, freshwater ecosystems
only cover 0.8% of the Earth's surface and contain 0.009% of its total water. There are three
basic types of freshwater ecosystems:
Lentic: Still or slow-moving water like pools, ponds, and lakes.
Lotic: Fast-moving water like streams and rivers.
The Food Chain:
Definition: A linear sequence of feeding relationships.
OR
The sequence of the transfer of food energy from one organism to another in an ecological
community. A food chain begins with a producer (autotrophs), usually a green plant or alga
that creates its own food through photosynthesis. In the typical predatory food chain, producers
are eaten by primary consumers (herbivores) which are eaten by secondary consumers
(carnivores), some of which may in turn be eaten by tertiary consumers (the top carnivore in
the chain).
Many species of animals in an ecological community feed on both plants and animals and thus
play multiple roles in the chain. Parasites feed on living tissues, generally without killing their
hosts, and may themselves be hosts to smaller parasites. In addition, organisms that die without
being eaten are consumed by detrivores, some of which serve as prey for other consumers. The
complex system of interrelated food chains in an environment is known as a food web.
There are two kinds of food chains
1) Grazing food chains.
2) Detritus food chains.
3) Parasitic food chain.
1) Grazing food chains:
Grazing food chains derive their energy directly from the sun. These are the chains that we are
familiar with because we can see them, and because they are more frequently described in
articles about energy flow through food chains.
Characteristics of Grazing Food Chain
1. These are directly dependent upon solar radiations as the primary source of energy and the
producers (green plants) synthesize their plant biomass by the process of photosynthesis.
Producers form the first trophic level.
2. Herbivores or primary consumers eat upon the producers and form the second trophic level.
3. Herbivores are in-turn eaten by different categories of carnivores forming the higher trophic
levels.
4. Grazing food chains are longer food chains and they always end at decomposer level.
EX. of grassland ecosystem
Grass→ Rabbit→ Fox→ Wolf→ Tiger
Grass→ Grasshopper→ Frog → Snake → Hawk
EX. of aquatic ecosystem
Phytoplankton →Zooplankton→ Fish→ Hawk
2) Detritus food chains: A detritus food chain is one in which the primary consumer feeds on
dead plant matter.
OR
This type of food chain starts from dead organic matter and so it is less dependent on solar
energy. The dead organic matter is broken down into simple nutrients by microorganisms like
fungi and bacteria. This type of food chain is found in forest ecosystem. ( This is decomposer
organism based )
Dead organic matter→ Detritivores → Predators
Characteristics of Detritus Food Chain
1. Primary source of energy is dead organic matter called 'detritus‘(non-living particulate organic
material) which are fallen leaves, plant parts or dead animal bodies.
2. Primary consumers are ‘Detritivores' including protozoans, bacteria, fungi, etc. which feed
upon the detritus saprophytically. (Saprophytic means absorbing nutrition from dead organic
matter).
3. Detritivores are in turn eaten by secondary consumers such as insect larvae, nematodes, etc.
4. Detritus food chains are generally shorter than grazing food chains
5. In nature, detritus food chains are indispensable as the dead organic matter of grazing food
chain is acted upon by the Detritivores to recycle the inorganic elements into the ecosystem
3. Parasitic food chain: In this type of food chain either the producer or the consumer is
parasitized and therefore 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
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. It explains the concept of bio magnification.
Carnivores eat other carnivores, as well as herbivores. Some may even eat both animals and
plants and are called omnivores. If we listed every species that occurred in an ecosystem and
then drew arrows connecting them to each of their food sources, we would see so many
crisscrossing arrows that it would give the appearance of a spider web. Therefore, we call the
entire complex array of feeding relationships in an ecosystem a food web.
In nature, food chain relationships are not isolated. They are very complex, as one organism may
form the food source of many organisms. Thus, instead of a simple linear food chain, there is a
web like structure formed by these interlinked food chains. Such interconnected matrix of food
chains is called 'food web'.
Food web: It can be defined as, "a network of food chains which are interconnected at various
trophic levels, so as to form a number of feeding connections amongst different organisms of a
biotic community". The complex array of feeding relationships in an ecosystem. A food web
consists of many interconnected food chains.
A network of food chains or feeding relationships by which energy and nutrients are passed on
from one species of living organisms to another.
Food webs are indispensable in ecosystems as they allow an organism to obtain its food from
more than one type of organism of the lower trophic level.
Generally, a food web operates according to taste and food preferences of the organism, yet
availability of food source and other compulsions are equally important.
Ecological pyramid:
An ecological pyramid (also trophic pyramid or energy pyramid) is a graphical representation
designed to show the biomass or biomass productivity at each trophic in a given ecosystem.
Biomass is the amount of living or organic matter present in an organism.
Biomass pyramids show how much biomass is present in the organisms at each trophic level,
while productivity pyramids show the production or turnover in biomass.
An ecological pyramid is a diagram that shows the relative amounts of energy or matter
contained within each trophic level in a food chain or food web.
An ecological pyramid is a graphical representation designed to show the number of organisms,
energy relationships, and biomass of an ecosystem.
They are also called Eltonian pyramids after Charles Elton, who developed the concept of
ecological pyramids.
Three Types of Pyramids
1. Pyramid of Biomass
2. Pyramid of Numbers
3. Pyramid of Energy
1. Pyramid of Biomass
Biomass is renewable organic (living) material. A pyramid of biomass is a representation of the
amount of energy contained in biomass, at different trophic levels for a particular time. It is
measured in grams per meter2, or calories per meter2. This demonstrates the amount of matter
lost between trophic levels. Each level is dependent on its lower level for energy, hence the
lower level determines how much energy will be available to the upper level. Also, energy is lost
in transfer so the amount of energy is less higher up the pyramid.
There are two types of biomass pyramids: upright and inverted.
1. An upright pyramid is one where the combined weight of producers is larger than the
combined weight of consumers. Example: Forest ecosystem.
2. An inverted pyramid is one where the combined weight of producers is smaller than the
combined weight of consumers. Example: Aquatic ecosystem.
2. Pyramid of Numbers
The pyramid of numbers represents the number of organisms in each trophic level. This pyramid
consists of a plot of relationships between the number herbivores (primary consumers), first level
carnivore (secondary consumers), second level carnivore (tertiary consumers) and so forth. This
shape varies from ecosystem to ecosystem because the number of organisms at each level is
variable.
Three types of pyramids of numbers : Upright, Partly upright and Inverted
3. Pyramid of Energy
The pyramid of energy represents the total amount of energy consumed by each trophic level. An
energy pyramid is always upright as the total amount of energy available for utilization in the
layers above is less than the energy available in the lower levels. This happens because during
energy transfer from lower to higher levels, some energy is always lost.