Today’s Topic
Food Chains
Learning Goal:
SWBAT explain the relationships that exist
between creatures on a food chain.
 Question:
In a given community, arrowhead plants are
able to provide 35,000 Joules of energy.
If there are five trophic levels in this
community, how many joules of energy can
the creatures at the highest tropic level
receive?
Trophic Levels
 As we have learned, as creatures eat one
another, their energy and matter move up
trophic levels.
Trophic Levels
 Another term for this is the food chain.
 A food chain is a linear series of feeding
relationships.
Primary
Producer
Primary
Consumer
Secondary
Consumer
Food Chains
 The arrows on a food chain indicate the
direction in which energy flows.
 Think of it as if “this does into this one’s
stomach”.
Primary
Producer
Primary
Consumer
Secondary
Consumer
Food Chains
 Both energy, biomass, and toxins are
transferred up the food chain.
 How could radiation in the Pacific Ocean
negative affect you and me?
Primary
Producer
Primary
Consumer
Secondary
Consumer
Food Chains
Primary
Producer
Primary
Consumer
Secondary
Consumer
 How many trophic levels are in this food
chain?
 What is the highest level consumer shown
above?
Food Chains
 How many trophic levels
are in this food chain?
 What is the highest level consumer shown
above?
Food Chains
 How many trophic levels are in this food
chain?
Food Chains
 In what way are food chains unrealistic?
 How may they not properly represent an
actual community?
Primary
Producer
Primary
Consumer
Secondary
Consumer
Food Chains
 Creatures in a community may eat more
than one type of food!
 To better show the relationships in a
community, food webs may be utilized.
Food Webs
 A food web is
a visual map
showing the
many paths
energy and
nutrients flow in
a community.
Food Webs
 Ecologists have found that certain creatures
have a much larger impact on a community
than others.
 Some creatures help to stabilize lower
trophic levels – even all the way to the first
levels!
Food Webs
 These types of creatures are known as
keystone species.
Keystone Species
 Much like if the keystone in an arch is
removed, the arch will collapse.
 If these keystone creatures are removed
from a community, a large portion of the
food web will be affected.
Keystone Species
 An example of this was found in 1990 off of
the coast of Alaska.
 It was found that orca whales ate many sea
otters.
Keystone Species
 As a result, otters in the area were not
eating as many sea urchins.
Keystone Species
 Because the sea urchin population
flourished, kelp forests in the region
declined and collapsed.
Keystone Species
 Due to the lack of kelp forests, fish and
other creatures that reside in the forest
were unable to survive.
Keystone Species
 This story is an example of trophic
cascade, where predators at high trophic
levels help organisms at low trophic levels
by limiting populations at intermediate
trophic levels.
Keystone Species
 To end this discussion, I have a video
regarding another keystone species.
 Enjoy!