Energy and the ecosystem
B M Subramanya Swamy M.Sc. B.Ed.
CIE Co ordinator & Examination Officer
Kanaan Global School
Overview of the topic
2.Food chains and web
3. Ecological pyramids
•Pyramid of numbers
•Pyramid of bio mass
• Ecology : Study of how organism interact with each other
& with their environment
• Environment – organism live
• Environment – divided into abiotic & biotic factor
• Abiotic factor-nonliving factor
• E.g. edaphic factor, climatic factor & topographical factor
• Biotic factor- living organism
• E g producer consumer decomposer
• Habitat – physical location in which an organism lives
Level of ecological organization
• Earth – lump of rock with a thin outer layer of soil, water & air.
• Organism occur near boundaries either between soil & air or water &
• Organism – studied at six different levels –
individual,population,community ecosystem, biome & biosphere
• Each species is made up of individual
• Guases competitive exclusion principle states- two species cannot
coexist unless there are significant difference in their ecologies. If 2
species attempt to occupy the same niche, they will compete with
each other until one is eliminated
• Niche – position of species occupied within its habitat.
• Niche includes physical space its interaction with other organism & its
effect on environment
• Individual – same species occupying a constitute a population
Different population in an area interact with each other. These collectively form a
Community – named after an obvious feature of the environment
– Pine forest community
– Woodland community
– Grassland community
• Different species of a community together with their non living
environment, constitute a ecosystem
• Ecosystem consists of 4 basic element
– Abiotic component
– Biotic component
– Energy & nutrient (support life in ecosystem)
• Ecosystem are open unit & part of a biome
• All the life are restricted to a rather narrow zone called the
The main energy source on the earth is sun.
Solar energy can be tapped by the plants to
Recently we are also able to tap this energy
source using solar panels.
Producers / consumers
• Green plants store solar energy in
carbohydrates during photosynthesis.
• They change solar energy into chemical
energy to achieve this
• They are producers (autotrophs): capable of
producing their own food.
• Consumers (heterotrophs) feed on producers
as a source of food.
Some terms associated with energy flow
Produces its own food e.g. green plants
Feeds on producers e.g. animals and man
Feeds on plants e.g. cattle
Feeds on animals e.g. lions
Feeds on plants and animals e.g. crows
Trophic level: All the organisms that
are the same number of food-chain
steps from the primary source of
Modified from: General Ecology, by David T. Krome
Foods chains and webs
• Producers and consumers play different roles in the
• These roles are termed as niches.
• The different niches can be classified in various ways
in the community.
• When a herbivore eats a plant, and is then eaten by a
carnivore, a chain of events from: based on feeding
• The forms the food chain.
Classification of niches in the food chain
1st trophic level
2nd trophic level
3rd trophic level
4th trophic level
5th trophic level
• Energy flows in one direction along food chain.
• Energy is transferred along the food chain.
• At the next level, energy is lost..therefore energy supplied from
level to level decreases.
• The more levels in the food chain, the lesser the energy at the end
of the chain.
• Green plants capture only 1% of solar energy.
• 10% of energy at every trophic level is converted into biomass.
• In reality, predators feed on more than one type of prey.
• When several different food chains can be strung together, it
forms a food web.
• A food web interconnects several food chains within an
•A graphical representation of the energy, biomass or numbers of
organisms at each trophic level.
•Each trophic level forms a tier in the pyramid
•They are called pyramids because of the shape of these graphs.
Pyramid of numbers and biomass
Pyramid of numbers
Pyramid of biomass
The base has the largest number of
Represents the dry mass of all the
organisms at that tropic level
The number of organisms reduce as you
reach the higher tiers of the pyramid
The lengths of the bars estimates the
May be upright of inverted
May be upright or inverted
An example of a pyramid of numbers
Pyramid of Energy:
• Shows the energy available at each trophic level.
– The size of the blocks represents the proportion of
– Measured in Joules or Calories
Pyramid of Energy:
• Most of the energy available to the community is in
the 1st trophic level.
• Only 10-20% of the energy is available to the next
trophic level (≈ 90% lost)
• Nutrients in the environment exist in various forms.
• Energy cannot be recycled, but the nutrients can
• Carbon is repeatedly recycled within the environment
•Carbon dioxide occupies about 0.03% by volume of air.
•This amount is sufficient for all plants that photosynthesis
•CO2 is removed from the air by green plants.
•It is replaced through respiration and by the combustion of fossil fuels.
• Passage of nitrogen within an ecosystem
• Nitrogen cycle is more complex biogeochemical cycle
• Atmosphere contain 79% nitrogen gas but only few
micro organism can tap this reservoir.
• Nitrogen fixation – nitrogen fixing bacteria
• Bacteria free-living or living in root nodules of
• Bacteria converts atmospheric nitrogen to nitrates
• Atmospheric nitrogen can also fixed by lightning
Denitrifying bacteria converts nitrates to nitrogen gas
– Bacteria are anaerobic
– Process is known as denitrification
Photosynthetic organisms make use of nitrates to form amino acids & protein,
which are in turn eaten by animals
Protein are broken down to amino acids in animals
Nitrogen in amino acids is excreted in the form of ammonia or urea
Decomposers breakdown protein molecules in dead animals and plants
Release nitrogen as ammonia or ammonium compounds- ammonification
E.g. putrefying bacteria
Ammonia or ammonium compounds to nitrites & nitrites to nitrates
Process is known as nitrification