Download Population Growth

Population
Growth
Population
group of individuals of the
same species living in the
same area, potentially
interacting
Population Growth
Four factors can affect population size:
-Birthrate – number of births
-Death rate – number of deaths
-Emigration – number of individuals moving
away from a population
-Immigration – number of individuals moving
into a population
A population can grow
when its birthrate is
greater than its death
rate.
Understanding Exponentials
Put your pens
down for a minute & think about
this:
An employer offers you two equal jobs for
one hour each day for fourteen days.
The first pays $10 an hour.
The second pays only 1 cent a day, but the
rate doubles each day.
Which job will you accept?
Understanding Exponentials
Job 1
90
80
70
60
50
40
30
20
10
0
Job 2
Now, how much would
your employer owe you
if you stayed at this job
for another 2 weeks?
Job 2 lags for a
long time before
exponential
growth kicks in!
1
2
3
4
5
What would happen if this
type of growth took place
within a population?
6
7
8
9
10
11
12
13
14
Exponential Growth
Under ideal conditions with unlimited
resources, a population will grow
exponentially.
Exponential growth occurs when the
individuals in a population reproduce at a
constant rate.
Exponential Growth
Logistic Growth
As resources become less available, the
growth of a population slows or stops.
Logistic growth occurs when a population's
growth slows or stops following a period of
exponential growth.
Logistic growth is characterized by an
S-shaped curve.
Carrying Capacity (K)
The largest number of individuals of
a population that a given
environment can support is called
its carrying capacity.
When a population reaches the
carrying capacity of its
environment, its growth levels off.
The average growth rate is zero.
What factors limit population
growth?
A limiting factor that depends on
population size is called a densitydependent limiting factor.
Density-dependent limiting factors include:
 Competition
(for food, water space, sunlight
and other essentials)
 Predation (predator- prey relationships)
 parasitism
 disease
What factors limit population
growth?
Density-independent limiting factors
affect all populations in similar ways,
regardless of the population size.
Examples of density-independent limiting factors
include:
 unusual weather
 natural disasters
 seasonal cycles

certain human activities—such as damming rivers
and clear-cutting forests
Focus Question
Monday, October 6th
What are the interactions
that occur within
communities?
Community Interactions
Community interactions,
such as competition,
predation, and various forms
of symbiosis can powerfully
affect an ecosystem.
Population – group of individuals of
the same species living in the same
area, potentially interacting.
Community – group of populations
of different species living in the same
area, potentially interacting.
What are some ecological interactions?
 Fitness
– how well an organism fits in its
environment.
Why are ecological
interactions important?
Interactions can affect
distribution and abundance.
Interactions can influence evolution.
Types of ecological interactions
competition
predation
parasitism
mutualism
commensalism
symbiosis
Competition – two species share a
requirement for a limited resource  reduces
survival of one or both species
Predation – one species feeds on another
 enhances fitness of predator but reduces
survival of prey
herbivory is a form of
predation
Parasitism – one species feeds on
another  enhances survival of parasite
but reduces fitness of host.
Mutualism – two species provide resources
or services to each other  enhances survival
of both species.
http://www.youtube.com/watch?v=X
m2qdxVVRm4
Commensalism – one species receives a
benefit from another species  enhances
survival of one species; no effect on fitness
of the other species.
http://www.youtube.com/watch?v=fkz
UziLiiDM
Symbiosis – two species live together 
can include parasitism, mutualism, and
commensalism.
Isle Royale near Lake Superior
Organizing ecological interactions
effect on species 1
+
effect on
species
2
+
mutualism
0
commensalism
-
predation
herbivory
parasitism
0
commensalism
predation
herbivory
parasitism
competition
competition
competition
 Choose
an organism and describe the
type of community interactions that
affect the success of that organism.
 List
the limiting factors of the carrying
capacity of the habitat
How would you describe the
trends seen within this graph?
Bunny
Fox
Grass
Time (Months)
Focus Question
Wednesday, October 9th
What types of human
activities can disturb an
ecosystem and cause
succession?
Monday October 10th
Write down your answer on a
separate piece of paper:
1.What is the difference between
an organism’s habitat and
niche?