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Populations
Population Dynamics
Population: a group of the same species that
interbreed and live in the same area at the
same time
Population Characteristics
 Density

How many egrets are there in an area of 2km²
 Dispersion



Uniform
Clumped
Random
http://glencoe.mcgraw-hill.com/sites/0078695104/student_view0/unit1/chapter4/concepts_in_motion.html#
Principles of Growth
 How
fast do populations grow?
 What are the limitations?
 Do organisms show patterns in their
growth?
http://www.otherwise.com/population/index.html
Population Ranges
What determines which animals live where?
A Bit of Review…
 Two Major Factors


Limiting Factors
Tolerance Ranges
 Other


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influencing factors:
Competitors
Predators
Parasites
What limits population growth?

Types of Limiting Factors

Density Independent
Any factor in the environment that does not
depend on the number of members in a
population per unit area
•
•
•
•
Usually abiotic
May cause a total wipeout
Examples of natural events:
Examples of Human alterations:
Types of Limiting Factors
 Density
Dependent
Any factor in the environment that depends on
the number of members in a population per
unit area.
 Usually biotic factors
• Predation
• Disease
• Competition


Occurs between same species and different species
Causes starvation or emigration to decrease competition
• Parasites
Effects of Competition
 Competition


When populations are low, resources are
plentiful
When populations increase, resources
become scarce-
What is the relationship of the hare and the lynx?
What might happen to the lynx if the producers in the area suffered a major decline?
Explain the relationship between the three populations of
organisms and how their growth or decline rate are related
to each other.
Explain what density dependent factor might have
influenced the two animal populations.
Population Trends
Hurry up already. I
am already two weeks
old. We have to have
as many kids as
possible before we are
ancient!
No worries….let’s travel
and see the Savannah
before we have kids.
I’m not ready yet. I
need to be able to
support my family first.
How fast can a population grow?
Small Organisms

Mosquito - r-strategist



Adapted to an unstable
environment
short life span – hurry up
many offspring
Large Organisms
 Elephant - k-strategist



Adapted to a stable
environment
Long life span – no hurry
Few offspring
Why the differences???
How fast can a population
grow?
 Populations
grow exponentially when
resources are unlimited.
An exponential Growth Curve
http://www.otherwise.com/population/index.
html
Population Growth
Limited by carrying capacity:

carrying capacity: the number of one species an
area can support
 Limitations include: oxygen, nutrients, water,
energy
 Causes a logistic growth
curve to occur
Logistic Growth Model
http://www.otherwise.com/population/index.html