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.