Ecology
Food chain
&
Ecological pyramids
M. Saadatian
www.soran.edu.iq
1
Food chain
&
Ecological pyramids
www.soran.edu.iq
Important facts about food chains
• In a food chain each organism obtains energy
from the one at the level below.
• Plants are called producers because they
create their own food through photosynthesis
• Animals are consumers because they cannot
create their own food, they must eat plants or
other animals to get the energy that they
need.
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There are two types of food chains
• Grazing food chain
• Detritus food chain
Grazing food chain – it starts from green plants (autotrophs or
producers) and ends to carnivores by passing through
herbivores. Thus, the gross production of plants may need
three fates.
The grazing food chain is of two types, namely,
• Predator chain
• Parasitic chain
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• Predator chain – here one animal captures and devours
another animal. The animal, which is being eaten, is called
prey and the animal, which eats it, is called predator. The
predator chain is formed of plants, herbivores, primary
carnivores, secondary carnivores and so on.
• Parasitic chain – the plants and animals of the grazing food
chain are infected by parasites. When the smaller organisms
(parasites) consume larger ones without outright killing of the
host, the food chain is called parasitic food chain.
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Detritus food chain – the organic wastes, exudates and dead
matter derived from the grazing food chain are usually called
detritus. The energy contained in this detritus serves as the
source of energy for a group of organisms (detritivores) that
are separated from the grazing food chain and generally
termed the detritus food chain.
• The organisms of the detritus food chain are algae, bacteria,
actinomycetes, fungi, protozoa, insects, mites, crustacea,
nematodes, etc. the detritus organisms gradually break down
the complex organic molecules present in the organic waste
or dead tissues into much simpler compounds (humic acids).
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Primary Producers
• Primary producers are “organisms capable of
producing their own food”
• We can also say that they are photosynthetic, use
light energy.
• Examples of primary producers include algae,
phytoplankton, and large plants.
• Primary producers are eaten by primary consumers
(herbivores)
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Ways to Classify Consumers
1. Primary Consumers: Herbivores.
2. Secondary Consumers: Carnivores that eat
herbivores.
3. Tertiary Consumers: Carnivores that eat
other carnivores.
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D. Trophic Levels—each step in a food chain or food web
1. Level 1—Producers (autotrophs)
2. Level 2—Primary Consumers (herbivores)
3. Level 3—Secondary Consumers
(carnivores or omnivores)
4. Level 4—Tertiary Consumers
(carnivore—usually top carnivore)
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Food chains
• Trophic levels
– feeding relationships
– start with energy from
the sun
– captured by plants
•
1st
Level 4
Tertiary consumer
top carnivore
Level 3
Secondary consumer
carnivore
Level 2
Primary consumer
heterotrophs
herbivore
level of all food chains
– food chains usually go
up only 4 or 5 levels
Level 1
Producer
• inefficiency of energy transfer
– all levels connect to
decomposers
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sun
autotrophs
Decomposers
Bacteria
Fungi
B. Food Chain—series of steps in which organisms transfer
energy by eating and being eaten
1. Arrows go in the direction of how energy is
transferred
2. Start with producer and end with top consumer
or carnivore
Ex: grass
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cricket
frog
raccoon
C. Food Web—network of food chains within an ecosystem
Hawks
Weasels
Raccoons
Mice
Grass
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Hawks
Food Webs
Raccoons
Weasels
Mice
Grass
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ECOLOGICAL PYRAMIDS
• Food chains and food webs do not give any
information about the numbers of organisms
involved.
• This information can be shown through
ecological pyramids.
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Ecological Pyramids
• An ecological pyramid is a diagram that shows the
relationship amounts of energy or matter contained
within each trophic level in a food web or food chain.
• Energy pyramids
• Number pyramids
• Biomass pyramids
• Energy Pyramid only 10% of the energy available within
one trophic level is transferred to organisms at the next
trophic level.
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Ecological Pyramids
A. Diagram that shows the relative amount of energy or
organisms contained within each trophic level of a food
chain or web
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Energy Pyramid
In nature, ecological
efficiency varies from
5% to 20% energy
available between
successive trophic
levels (95% to 80%
loss). About 10%
efficiency is a general
rule.
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Fig. 4–19
PYRAMID OF NUMBERS
• Shows the number of organisms at each
trophic level per unit area of an ecosystem.
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Pyramid of Numbers
Pyramid of numbers displays the number of individuals
at each level.
1 owl
25 voles
2000
grass plants
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PYRAMID OF BIOMASS
 The total amount of matter present in
organisms of an ecosystem at each trophic
level is biomass.
 Biomass is preferred to the use of numbers of
organisms because individual organisms can
vary in size. It is the total mass not the size
that is important.
 Pyramid of biomass records the total dry
organic matter of organisms at each trophic
level in a given area of an ecosystem.
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Biomass Pyramids
Displays the biomass at each trophic level.
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Pyramids Continued
Biomass pyramids show the total amount of living
tissue available at each trophic level. This shows the
amount of tissue available for the next trophic level.
Numbers pyramid shows the number of species at
each trophic level.
Because each trophic level harvests only about one
tenth of the energy from the level below, it can
support only about one 10th the amount of living
tissue.
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Energy Pyramid shows relative amount of energy available at each
trophic level
1. Organisms in a trophic level use the available
energy for life processes (such as growth,
photosynthesis, cellular respiration, metabolism,
etc.)and release some energy as heat
Remember: Every chemical process that happens in
your body releases heat as a byproduct (ex: burning
calories).
2. Rule of 10—only about 10% of the available energy
within a trophic level is transferred to the next
higher trophic level
Biomass Pyramid—represents the amount of living
matter at each trophic level
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organic
0.1%
1%
10%
100%
Energy Pyramid
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Biomass Pyramid