This is the third lesson of the course; 'Foundation of Environmental Management' taught at the Faculty of Social Sciences and Humanities of the Rajarata University of Sri Lanka

1. Lesson 3 – Ecosystems and Energy Flow
P.B. Dharmasena
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Foundation of Environmental Management
Course code: EMGT 2114

2. Course Content
1.Concepts of Ecology and Environmental Biology
2.Biogeochemical Cycles (C, N, P etc.)
3.Ecosystems and Energy Flow

3. • An ecosystem is a natural unit composed of living organisms
and their non-living environment.
3
Ecosystems

4. • A habitat is the place where an organism lives.
4
Habitats

5. Niche
• An organism’s niche is the role it plays within the ecosystem
5

7. •All organisms MUST
obtain and use energy…
Energy Flow through ecosystems

8. ENERGY ROLES (JOBS) IN ECOSYSTEMS
Each organism in an ecosystem has a role or niche.
• Producer’s Role – make their own food through photosynthesis,
convert the Sun’s energy to make glucose, provide food for 1st and 3rd
level consumers.
• Examples: Any plant… Grasses, shrubs, trees, algae… etc.

9. • 1st Level Consumer (Herbivores) Role-must consume another
organism to obtain energy, ONLY CONSUME PLANTS,
provide food for 2nd and 3rd level consumers.
• Examples: Deer, rabbits, rodents (mice, rats, squirrels), insects,
herbivorous birds, etc.
ENERGY ROLES (JOBS) IN ECOSYSTEMS

10. • 2nd Level Consumer (Carnivores) Role-must consume another
organism to obtain energy, ONLY CONSUME OTHER
CONSUMERS, provide food for 3rd level consumers.
• Examples: snakes, foxes, predatory birds, jellyfish etc.
ENERGY ROLES (JOBS) IN ECOSYSTEMS

11. • 3rd Level Consumer (Omnivores and Large Carnivores) Role-
must consume another organism to obtain energy,
CONSUMES OTHER CONSUMERS and/or PRODUCERS,
provide food for scavengers.
• Examples: Humans, lions, bears, sharks, whales.
ENERGY ROLES (JOBS) IN ECOSYSTEMS

12. • Scavenger’s Role-must consume another organism to obtain
energy, CONSUMES DEAD ANIMAL REMAINS, provide
food for other scavengers.
• Examples: Hyenas, eagles, flies, snails.
ENERGY ROLES (JOBS) IN ECOSYSTEMS

13. ENERGY FLOW
• Food Chains: shows ONE possible path for the flow of
energy for a particular organism in an ecosystem.
• Rules:
A. Must start with producers to 1st level consumer to 2nd,
and so on.
B. Must use arrows to show the direction of energy flow.
Organism that is
eaten
Organism that is
eating

14. Food chain examples

15. •Food Web: Many overlapping food chains in an
ecosystem.
• Shows relationships & dependencies to others.
•Rules:
A. Must start with producers to 1st level
consumer to 2nd, and so on.
B. Must use arrows to show the direction of
energy flow (arrows may overlap).
ENERGY FLOW

16. Food
web
example

17. Food web example

18. Food web example

19. •Energy Pyramids: Shows the flow of energy in a
food chain with LESS energy as each level goes
up.
•Rules:
A. Producers go on the bottom, 3rd level
consumer on top.
B. Must have more producers than 1st level
consumers, more 1st than 2nd , more 2nd than
3rd, etc.
Energy Flow

20. ENERGY PYRAMID

23. •Autotrophs: Organisms that can make their own
food. (Producers)
•Heterotrophs: Organisms that cannot make their own
food, they must consume. (Consumers, Scavengers,
Decomposers)
Two Types of Organisms

24. Energy Flow and Loss
• Not all the energy available at
each step in a food chain is
passed onto the next step.
• Only about 10% is passed on.
• 90% of the energy is lost e.g.
as:
• Movement
• Heat production
• Waste.

25. Friday, December 21, 2018 Mr G Davidson 25
Grass
Greenfly
Ladybird
Thrush
Number of
organisms decrease
Size of organisms
increase
Pyramid of Numbers • A pyramid of numbers is a
diagram which represents the
number of organisms at each
stage in a food chain.