Community Interactions:
Food Chains & Food Webs
Review-What is Ecology?

Ecology
 The
study of interactions of organisms
and the physical environment.
 All
about interactions and interdependence
between organisms and their environment
 Encompasses
a variety of topics ranging
from food webs and energy flow to human
population growth.
Levels of Organization

To understand relationships on Earth,
ecologists study many different levels of
organization of organisms.
 population  community 
ecosystem  biome  biosphere
 Individual
 Increase
in scope and complexity as go
from individual to biosphere.
Individual

Individual = a single organism; a member of a
population

All organisms occupy a specific habitat and
niche.

Niche = organism’s job or role

Habitat = where the organism lives (think of it as
an organism’s address)
Population – Community

Population = a group of individuals that
belong to the same species &
live in the same general area

Community = an assemblage of populations
interacting with one another
within the same environment
Ecosystem – Biome

Ecosystem = biological community together
with the associated abiotic
(non-living) environment
Biome = a geographical region containing
several ecosystems that have the
same climate & dominate
communities
* We live in the Temperate Deciduous Forest
Biome

Biosphere

Biosphere = the
portions of the
planet in which
life exists
(including land,
water, &
atmosphere)
Checking your understanding–
Quick Questions
1.
2.
3.
4.
5.
6.
What is ecology?
How are organisms organized (6 levels)?
What is the difference between an organism’s
habitat and its niche?
What is an assemblage of interacting
populations?
What is the difference between a community
and an ecosystem?
What term describes all living parts of the
earth?
How do nutrients and energy
flow in an ecosystem?


Food chains are representations of the order in
which one population feeds on another in an
ecosystem.
Example: Algae  Fish  Humans
Food webs are complex patterns of energy
flow in an ecosystem represented by several
interconnected food chains.
Example of an Aquatic Food Web
3 Major Trophic Levels–
Level 1

Autotrophs

Also referred to as producers

Require only inorganic nutrients and an outside energy
source to produce organic nutrients

Includes:
 Primarily photosynthetic organisms which are
organisms that convert the sun’s energy into food
(ex: plants)
 Other types exist
3 Major Trophic Levels–
Level 2

Heterotrophs
Also referred to as consumers
 Must obtain their nutrients and energy from
producers
 Includes:
 Herbivores– primary consumers
 Carnivores– secondary and tertiary
consumers
 Omnivores– primary, secondary, and tertiary
consumers

3 Major Trophic Levels–
Level 3

Decomposers

Organisms that break down dead organic matter

Decomposers play an important role in
ecosystems– they recycle nutrients!

Includes
 Non-photosynthetic
and mushrooms
bacteria and fungi such as molds
Guided Practice: Example of an
Aquatic Food Web
It’s your turn to try…




Can you apply the concepts that we’ve discussed today?
Please partner with the person sitting next to you.
Together, use the following terms to create a food web:
- oak tree
- hawks
- fox
- humans
- squirrels
- berries
- blue birds
- rabbits
- white-tailed deer
- mice
- fungi
- grass
Remember to include all the organisms in your food web. Be
prepared to explain why you created your food web the way
that you did. Put your food web on the large construction
paper.
Ticket to Exit

What are some of the foods that you consume
everyday?

Based on what we discussed in class, where do
you fit into the food web?

Why are food webs considered to be a more
accurate picture of what’s happening in
ecosystems than food chains?
Bell Activity: Quick Write
Write down an example of a food chain
with 4 organisms. Next to each one, write
down its niche. (Remember: A niche is its
job.)
Energy Flow through an
Ecosystem

The sun provides energy for the Earth. It is
either reflected or absorbed.


Water, land, clouds, human-made structures, and
plants absorb 70% of the solar energy reaching the
earth.
1-2% of the solar energy that reaches the earth is
absorbed by plants and trapped by chlorophyll

Solar energy is then converted to chemical energy by
the process of photosynthesis:
6 CO2 + 6 H2O + solar energy  C6H12O6 + 6 O2
Pyramid of Energy

Biomass = the total amount (mass) of all
organic matter at any level in the
food chain

Biomass is always greater, the lower the trophic
level.


Therefore, there is more producer biomass (plants)
than herbivore biomass (primary consumers) etc.
The biomass of organisms in a food chain
always forms a pyramid.
Pyramid of Energy (cont.)


To carry on its life processes, the plant uses most of
the energy trapped during photosynthesis. Only a
small part of the energy trapped by the plant remains
stored in the plant when it is harvested (this is what is
available to herbivores).
If a plant receives 1,000 Calories of energy from
the sun, about 5 Calories will be stored in the
plant and be available to herbivores. Generally,
only about 10% of the biomass at one level is
converted to biomass at the next level. So where
does the energy go as you move up the trophic
levels?
9/9 Question of the day:

How much energy moves from one trophic level
to the next?

Where does that “lost” energy go?

Write down one example of a food chain with
three to four organisms. Which is a better
depiction of energy flow in an ecosystem: food
web or food chain?
Pyramid of Energy (cont.)

Let’s look at an example:
If a deer eats a plant, less than one Calorie (less
than 20% of the energy stored in the plant) will
be converted to body tissue.
 25% of the energy is excreted through waste.
 More than half of the energy is changed to heat
energy.

Key Point: Energy is Lost
Between Trophic Levels

Food webs are limited in size because energy is
lost between trophic levels.

The 10% Rule
 Only about 10% of the energy is available
from one trophic level to the next.
Pyramid of Energy

Shows energy flow through an ecosystem
* 90% of energy is lost
to heat at each trophic
level.
* Only 10% of
energy is available
to next level

0.1%
Energy
Tertiary Consumers (ex: hawk)
1% Energy
Secondary Consumers (ex: snake)
10% Energy
Primary consumers (ex: rabbit)
100% Energy
Producers (ex: grass)
Note: Other types of pyramids exist (biomass pyramids
and pyramid of numbers).
Quick review of Energy Flow

The figure above shows energy flow in a simple
food chain. At each level of the food chain, about
90% of the energy is lost in the form of heat. The
total energy passed from one level to the next is
only about one-tenth of the energy received from
the previous organism. Therefore, as you move up
the food chain, there is less energy available.
Animals located at the top of the food chain need a
lot more food to meet their energy needs.
Read the statement below:
STATEWIDE ADVISORY
 Pennsylvania has issued a general, statewide
health advisory for recreationally caught sport
fish. The advice is that you eat no more than
one meal (one-half pound) per week of sport
fish caught in the state’s waterways. This general
advice was issued to protect against eating large
amounts of fish that have not been tested or
that may contain unidentified contaminants.
What does this mean and
why does this happen?
Think about it…
Terms to describe this:

Bioaccumulation is a general term for the
accumulation of substances, such as pesticides
(DDT is an example), methylmercury, or other
organic chemicals in an organism or part of an
organism.

How does this relate to the fish advisory you
read earlier?

Biomagnification is the bioaccumulation of a
substance up the food chain by transfer of
toxins in smaller organisms that are food for
larger organisms in the chain.

It results in higher concentrations of toxins in
organisms at higher levels in the food chain (at
higher trophic levels).