Transcript 9.4 Carrying Capacity

Carrying Capacity

Catalyst
 Humans
cut down 2.4 acres of rainforest (about the size
of two football fields) EVERY SECOND. We estimate
that 137 species go extinct every day as a result.
 How
does deforestation affect biodiversity?
 Are rainforest ecosystems more or less stable due to
deforestation?
 There
are two forests, “A” and “B.” The same disease
spreads through both forests, but Forest A changes
more than Forest B. What does this tell us about
biodiversity of Forest A compared to Forest B?
Objectives
By the end of today, all SWBAT…
 Ace the quiz!
 Predict if population size will
grow or decay based upon
limiting factors and carrying
capacity
Yesterday’s Exit Question
Read the passage at right to
answer the questions below:


How does trawling affect
coral reef biodiversity?
Would the coral reef be
more or less stable after
trawling? Explain why,
and be SPECIFIC.

(Hint: describe what
happens to all the
organisms in the coral reef
ecosystem, and use the
word “biodiversity.”)
Many organisms live in coral reefs, such
as plankton and algae, hundreds of
species of fish, sea urchins, and eels.
All of these organisms depend on the
coral to survive: they live inside of it,
use it for shelter, eat it, etc.
Trawling is the process of dragging a
gigantic rake across the bottom of
the ocean floor to scoop up
organisms. This is a very good way
to catch fish, but has the unfortunate
side effect of destroying nearly all
the coral in the trawler’s path.
Catalyst Review

Humans cut down 2.4 acres of rainforest (about the
size of two football fields) EVERY SECOND. We
estimate that 137 species go extinct every day as a
result.
 How
does deforestation affect biodiversity?
 Are rainforest ecosystems more or less stable due to
deforestation?
Catalyst Review

There are two forests, “A” and “B.” The same
disease spreads through both forests, but Forest A
changes more than Forest B. What does this tell us
about biodiversity of Forest A compared to Forest
B?
Quiz!

Put away your binders…
Turn
your desks into rows…
And
let’s ace that quiz!
You have 15 minutes
How Many?

We’ve been talking about populations of organisms
increasing or decreasing in size…
 When
new predators come
 When organisms leave the food web

But what controls how many organisms exist in a
population in the first place?
What determines population?

Why can’t we have…1,000,000 students here at
L.W. Higgins?
 Space
 Teachers
 Supplies
 Student
Behavior
These
resources are
our limiting
factors
Carrying Capacity

Key Point #1: An environment can only support
as many organisms as there is available food,
water, and free space
 Carrying
capacity = maximum number of organisms
that can live somewhere, based on the food, water,
and free space there
 Every species has a different carrying capacity.
Food, water, and free space are the
LIMITING FACTORS that determine
carrying capacity
Imagine Your Fridge
Your fridge is like
all of the resources
(food, water, free
space) in an
ecosystem.
What if we want to
throw a party?
Imagine Your Fridge
We can keep
inviting people,
as long as
there’s enough
food in the
fridge.
But with each
new guest,
there’s less to
go around.
Imagine Your Fridge
The fridge won’t replenish magically, and I don’t have
the money to keep putting food in the fridge
forever.
So too many guests means that…
So too many animals means that…
Someone goes hungry…
Not enough food/water/free space…
And leaves the party. 
And organisms die. 
Carrying Capacity

Key Point #2: We can read a carrying capacity
graph to predict changes in population size
C
Population size
D
A
B
Time
Carrying Capacity
C
Population size
D
A
B
Time

When a population is BELOW its carrying capacity,
it will INCREASE EXPONENTIALLY in size
Carrying Capacity
C
Population size
D
A
B
Time

But if it increases too much and rises ABOVE its
carrying capacity, it will DECREASE in size
Carrying Capacity
C
Population size
D
A
B
Time

This happens over and over… but the increases and
decreases get smaller and smaller…
Carrying Capacity
C
Population size
D
A
B
Time

Until eventually, the population size BECOMES
STABLE AT THE CARRYING CAPACITY
Carrying Capacity
C
Population size
D
A
B
Time
Closing

An environment can only support as many organisms
as there is available food, water, and free space
 Carrying
capacity = maximum number of organisms
that can live somewhere based on these limiting factors

We can read a carrying capacity graph to predict
changes in population size
 Below
carrying capacity = exponential growth
 Above carrying capacity = decease
 Over time, population stabilizes at carrying capacity
Exit Questions
C
Population size
D
A
B
Time

In the highlighted section of the graph, the
population is about to decline. Why? BE SPECIFIC!