ECOSYSTEM PART-1
DR. RANJANA
BHANDARI
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CHAPTER 2 ECOSYSTEMS AND BIODIVERSITY
2.1 Ecosystem -living things in a given area, non-living chemical and physical
factors of their environment, linked together through nutrient cycle and energy
flow
Types of Ecosystem
Natural Artificial/Man-made
Terrestrial Aquatic
Marine Fresh water
Lotic -river, stream or spring. Lentic -lake, pond or swamp.
2.2.1 Ecology – Study of the distribution and abundance of organisms, the flows of energy and
materials between abiotic and biotic components of ecosystems.
2. Ecosystem Structure: The living components of an ecosystem
• The roles of organisms in an ecosystem:
• Producer (autotrophy): make food; plants, algae
• Consumer (heterotrophy): eat other organisms
• Decomposer: eat dead organic matter; bacteria and fungi
1. Classes of Consumers
Herbivore – primary consumer – eats plants
Carnivores – secondary – meat eaters; eat herbivores
Tertiary – feed on carnivores
Omnivores – eat plants/animals.
2. Role of Organisms
Scavengers – feed on dead organisms (vultures, flies, crows, lobsters)
Detritus feeders – organisms that extract nutrients from fragments of dead organisms into more
simple organic waste (termites, earthworms, crabs)
Decomposers – organisms that digest parts of the dead organisms into simplest chemicals (bacteria,
fungi)
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Fig. 2.2.2 Role of organisms
3. FOREST ECOSYSTEM (TERRESTRIAL ECOSYSTEM)
1. Introduction
❖ A forest is an area with a high density of trees.
❖ World’s total land area is 13,076 million hectares – (Source: FAO; 1989)
❖ Of which total forests account for about 31% of the world’s land area.
❖ In India, the forest cover is roughly 19% of the total land area.
❖ The forest ecosystems are of great concern from the environmental point of view.
❖ It provides numerous environmental services like;
➢ Nutrient cycling,
➢ Maintaining biodiversity
➢ Providing wildlife habitat
➢ Affecting rainfall patterns
➢ Regulating stream flow
➢ Storing water
➢ Reducing flooding
➢ Preventing soil erosion
➢ Reclaiming degraded land & many more….
❖ Apart from environmental values, forest ecosystems have some traditional values as well.
❖ Examples are:
➢ Fire Wood & Timber.
➢ Fruits.
➢ Gums.
➢ Herbs & drugs.
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2.3.2 Structure and Function of Forest Ecosystem
I. Biotic components
❖ The various biotic components, representatives from the three functional groups, of a
forest ecosystem are:
1) Producer Organisms
❖ In a forest, the producers are mainly trees.
❖ Trees are of different kinds depending upon the type of forest developed in that climate.
❖ Apart from trees, climbers, epiphytes, shrubs and ground vegetation.
❖ Dominant species of trees in major types of forest ecosystems are:
❖ Tectona grandis, Acer, Betula, Picea, Pine, Cedrus.
2) Consumers
❖ In a forest, consumers are of three main types;
a) Primary Consumers
❖ These are Herbivores which feed directly on producers.
Eg:
❖ Ants, Beetles, Bugs, spiders etc. feeding on tree leaves.
❖ Larger animals such as Elephants, Deer, giraffe etc. grazing on shoots
and/or fruits of trees.
a) Secondary Consumers
❖ These are carnivores and feed on primary consumers.
Eg: Birds, Lizards, Frogs, Snakes and Foxes.
c) Tertiary Consumers
❖ These are secondary carnivores and feed on secondary consumers
❖ These include top carnivores like Lion, Tiger.
3) Decomposers
❖ These include wide variety of saprotrophic micro- organism like;
❖ Bacteria (Bacillus Sp., Clostridium sp., pseudomonas.
❖ Fungi (Aspergillus sp., Ganoderma sp., Fusarium.
❖ Actinomycetes (Streptomyces).
❖ They attract the dead or decayed bodies of organisms & thus decomposition takes place.
❖ Therefore, nutrients are released for reuse.
II. Abiotic components
❖ These include basic inorganic & organic compounds present in the soil & atmosphere.
❖ In addition dead organic debris is also found littered in forests.
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Fig.2.3 Forest Ecosystem
4. GRASSLAND ECOSYSTEM (TERRESTRIAL ECOSYSTEM)
1. Introduction
❖ Grasslands (also called Greenswards) are areas where the vegetation is dominated
by grasses and other herbaceous (non-woody) plants.
❖ Grasslands occupy about 24% of the earth’s surface.
❖ Grasslands occur in regions too dry for forests and too moist for deserts
❖ The annual rainfall ranges between 25- 75 cm, Usually seasonal
❖ The principal grasslands include:
➢ Prairies (Canada, USA),Pampas (South America),Steppes (Europe & Asia)
Veldts (Africa)
❖ The highest abundance & greatest diversity of large mammals are found in these ecosystems.
❖ The dominant animal species include
❖ Wild horses, asses & antelope of Eurasia,
❖ Herds of Bison of America; and
❖ The antelope & other large herbivores of Africa.
2.4.2 Structure and functions of Grassland Ecosystems
I. Biotic components
1) Producer Organisms
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❖ In grassland, producers are mainly grasses; though, a few herbs & shrubs also contribute to
primary production of biomass.
❖ Some of the most common species of grasses are:
❖ Brachiaria sp., Cynodon sp., Desmodium sp., Digitaria sp.
2) Consumers
❖ In a grassland, consumers are of three main types;
a) Primary Consumers
❖ The primary consumers are herbivores feeding directly on grasses. These are grazing animals
such as
❖ Cows, Buffaloes, Sheep, Goats, Deer, Rabbits etc.
❖ Besides them, numerous species of insects, termites, etc are also
present.
b) Secondary Consumers
❖ These are carnivores that feed on primary consumers (Herbivores)
❖ These include;-Frogs, Snakes, Lizards, Birds, Foxes, Jackals etc.
c) Tertiary Consumers
❖ These include hawks etc. which feed on secondary consumers.
1) Decomposers
❖ These include wide variety of saprotrophic micro- organism like: Bacteria; Fungi;
Actinomycetes
❖ They attract the dead or decayed bodies of organisms & thus decomposition takes place.
❖ Therefore, nutrients are released for reuse by producers.
II. Abiotic components
❖ These include basic inorganic & organic compounds present in the soil & aerial environment.
❖ The essential elements like C, H, N, O, P, S etc. are supplied by water, nitrogen, nitrates,
sulphates, phosphates present in soil & atmosphere.
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Fig.2.4 Grassland Ecosystem
5. DESERT ECOSYSTEM
1. Introduction
❖ A desert is a landscape or region that receives almost no precipitation.
❖ Deserts are defined as areas with an average annual precipitation of less than 250 millimeters
per year.
❖ It occupies about 17% of the earth’s surface.
❖ Deserts are characterized by hot days & cold nights.
❖ The deserts of the world are mainly located in the
South- western United States, Mexico, North
America, Asia (Thar, Gobi, Tibet) & west Asia.
❖ Deserts are characterized by scanty flora & fauna.
❖ Soils of deserts often have abundant nutrients but little or no organic matter.
2. Sturucture and Functions of Desert Ecosystms
I. Biotic components
1) Producer Organisms
❖ In a desert, producers are mainly shrubs/bushes; some grasses & a few trees.
❖ Dominant plant species include: Succulents (water – retaining plants adapted to arid climate
or soil conditions) & hardy grasses.
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❖ Besides some lower plants such as lichens & xerophytic mosses are also present.
2) Consumer Organisms
These include animals such as insects, reptiles which are capable of living in xeric conditions
❖ Besides some nocturnal rodents, birds & some mammalians like camel etc are also found.
3) Decomposers
Due to poor vegetation with very low amount of dead organic matter, decomposers are poor in
desert ecosystem.
❖ The common decomposers are some bacteria & fungi, most of which are thermophillic.
II. Abiotic components
Due to high temperature & very low rainfall, the organic substances are poorly present in the soil.
Fig. 2.5 Forest Ecosystem
6. AQUATIC ECOSYSTEMS
1. Introduction
❖ Aquatic ecosystems deal with biotic community present in water bodies.
❖ In terrestrial ecosystem, carbon dioxide & oxygen are present in gaseous form whereas in
aquatic ecosystem, these are available in dissolved state.
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