2016-11-10
Energy Flow in Ecosystems
Let’s refresh:
•  What is an ecosystem?
•  Give an example of an abiotic and a
biotic factor.
•  What happens during photosynthesis?
•  What happens during cellular
respiration?
–  Are these two related? How?
•  Define and give examples of
each:
– Herbivore
– Carnivore
– Omnivore
Biotic Factors
Alternate
Name
Energy
Source
Example
Trophic Levels
•  Categorize living things (biotic
factors) according to how
they gain their energy.
Producer
Consumer
Autotroph
Heterotroph
•  Make (produce)
their own food
•  From sunlight and
basic nutrients
(abiotic factors)
Plants
•  CANNOT make their
own food
•  Must obtain it from
autotrophs or other
heterotrophs (biotic
factors)
Herbivores
Omnivores
Carnivores
1st Trophic Level
•  Contains organisms that are able to make their
own food from abiotic factors (e.g. soil
nutrients, sunlight)
•  Organisms in the 1st trophic level are called
producers______ or ___autotrophs___
•  E.g.
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2nd Trophic Level
•  Contains organisms that feed on producers
•  Rely DIRECTLY on producers for their source
of energy.
3rd Trophic Level
•  Contains organisms that rely on primary
consumers as their main energy source
•  But, indirectly, are still dependent on producers
•  Organisms in the 2nd trophic level are called
herbivores/ primary consumers/ heterotrophs_
•  Organisms in the 3rd trophic level are called
__secondary consumers______________
•  E.g.
•  E.g.
Decomposers
•  Organisms that feed on waste from biotic
factors, including their dead remain
•  Return nutrients (abiotic factors) to the
ecosystem
•  E.g.
4th Trophic
Levels
3rd Trophic
Levels
2nd Trophic
Levels
1st Trophic
Levels
Food Chains
4th Trophic
Levels
3rd Trophic
Levels
2nd Trophic
Levels
1st Trophic
Levels
•  Step-by-step sequence
linking organisms that feed
on each other
•  Arrows show the flow of
energy (“is eaten by”)
•  Do not exist in nature
•  Show simple feeding
relationships
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Food Webs
•  In reality, each organism has a variety of
food sources and is therefore involved in
multiple food chains
•  These food chains interlock to form a
complex food web
Food Web: Representation of the complex
feeding relationships in an
ecosystem
Energy Flow
•  Organisms use about 90 % of the
energy they take in to grow and
reproduce, leaving just 10% of the
energy they receive to pass along to
the next trophic level.
Ecological Pyramids
•  Are used to organize the information of these
transfers, and the most common are:
Type
Pyramid of
numbers
Pyramid of
Biomass
Pyramid of
Energy
Based on…
Population of
Organisms
Mass of
Organisms
Stored energy
in organisms
grass → grasshopper → frog → snake →
hawk
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