Food Webs & Trophic Relations
What we all need! In order for any critter to live and survive it
needs one thing… Food!
– Why?
Food is like gasoline for your
car – or the batteries for your
flashlight – it is the source of
our energy.
Without food, all critters would
starve and eventually die from
the lack of energy. We need
food to get the energy we need
to move and do other bodily
functions like digest, think and
much much more.
When your body tells you its
hungry, like a fuel sensor, it’s
telling you that it needs more
fuel for energy.
Food & Ecosystems:
All organisms get their food from their
surrounding environment. This is what
makes up an Ecosystem.– An ecosystem is an area of nature in which living things (Biotic) and
non-living things (Abiotic) interact to exchange energy and
materials.
– Without Energy and Abiotic factors, life would not survive.
– There are many different types of ecosystems:
How does food and energy fit into
the big picture of life?
Like Plants and Animals…
Like dirt and water…
Producers:
Flowers
Cactus
All grasses
Trees
Just about every type of plant
These “produce” their own
food (energy) for themselves
and in turn for everything
else… Autotrophs (Auto=self)
They use Photosynthesis to
get energy
Primary Consumers
Cows
Giraffe
Deer Some Bugs
Primary consumers get their energy by eating the Producers.
Critters that eat plants…
Secondary Consumers
Lions…
Tigers…
And Bears…Oh my!!!
Secondary consumers eat the Primary consumers
Critters that can eat both
producers and consumers
are called “Omnivores”
Humans are an example of Omnivores!!!
Decomposers get energy from
decaying dead stuff!Bacteria
Worms
Mushrooms
Bugs
All give off CO2
Food Chains - Simplified
Food chains can be useful because the simply show a
single path of energy through an ecosystem
2. Chemical Energy 2. Chemical Energy
Food WebA food web is more like several food
chains put together and is more
representative of energy flowing
through a true ecosystem – because it
shows what each critter truly eats to
get its energy.
Food Web
The arrows show the flow of energy
from one organism to another
There are pictures to represent
each organism and level of Food Webs
Decomposers
Secondary consumers
Primary consumers
Producers
All proper food webs begin with the sun
Energy Pyramid
Producer(100 units)
Primary
Consumer(10 units)
Secondary
Consumer(1 unit)
10%
10%
If this pyramid represents amounts of
energy flowing in an ecosystem, why
does the pyramid have a wide base at the
bottom and is narrow at the top?
That’s because most (90%)
of the energy gets utilized
as irretrievable mechanical
and heat energy and the
leftover chemical energy
(10%) moves to the next
trophic level.
Another word for this loss of
energy is called entropy.
Food Chains & Flow of Energy
Mechanical
(Bio-Processes)
Heat
(Due to Processes)
Chemical
(Meat/Fat)
Mechanical
(Bio-Processes)
Heat
(Due to Processes)
Plants
Producer
Primary
Consumer
Secondary
Consumer
Chemical
(Meat/Fat)
Chemical
(sugar)Light (Sun)
10% 10%10%
1. Light Energy 2. Chemical Energy3. Mechanical & Heat
Energy
In this slide, notice that only
10% of the energy caries over
from the previous trophic level –
that’s because both mechanical
and heat energy are lost in the
environment and cannot be
retrieved. (Entropy)
Food Chains & Flow of Energy
Mechanical
(Bio-Processes)
Heat
(Due to Processes)
Chemical
(Meat/Fat)
Mechanical
(Bio-Processes)
Heat
(Due to Processes)
Plants
Producer
Primary
Consumer
Secondary
Consumer
Chemical
(Meat/Fat)
Chemical
(sugar)Light (Sun)
10% 10%10%
1. Light Energy 2. Chemical Energy3. Mechanical & Heat
Energy
The loss of energy in the
environment via mechanical
and heat energy explains why
the pyramid is wide at the base
and narrow at the top.
Food Chains & Energy Allocation
Therefore, if a food chain represents a linear path of energy in an ecosystem, we must consider where the energy is truly being allocated.
2. Chemical Energy 2. Chemical Energy
90% 90%
10% 10%
100%
Energy Pyramid
Pla
ntsSugar & O2
CO2 & H2O(Mechanical & Heat)
CO2 & H2O(Mechanical & Heat)
When we utilize our model, notice that our source of energy is
the sun, then plants convert light energy into chemical energy
and transfer it to the primary consumers. That energy then
gets transferred up to the secondary consumers. You should
also notice the exhausted and irretrievable mechanical and
heat energy traipse off to the side as chemical energy
transfers up the pyramid.
Trophic Pyramid
Trophic pyramid with efficiency of energy transfer
Since only 10% of our original piece of energy moves up each trophic level
each time, our pyramid should be better represented by the pyramid below.