POPULATIONS
Definition:
All the members of a species that live
in one place at one time.
PROPERTIES of Populations

Population SIZE


Population DENSITY


The number of individuals in a population
Number of individuals per unit of area
DISPERSION

SPATIAL distribution of individuals within the population



Uniform
Random
Clumped
PROPERTIES of Populations
Population Growth RATE
Definition
 The amount by which a population’s size
changes over time.
Population Growth RATE

Depends on:




Birth +
Death Emigration: movement of individuals OUT OF a
population
Immigration: movement of individuals INTO a
population
+
2 Types of Population Growth
1.
2.
Exponential
Logistic
EXPONENTIAL Model of Population Growth



Population increases rapidly with no limit
“J” shaped curve
What will a graph look like?
Rare in nature. Why?
Limit on the amount of resources (food / space)
LOGISTIC Model
ofAsPopulation
populationGrowth
reaches
carrying capacity,
 death
Accounts
forincreases
influence of
rate
limiting factors (like food,
space)
When
at carrying capacity,
 What will the graph look
birth
like? rate is equal to
death rate
“S”
WhenStretched
populationout
is small,
birth rate is higher
than death rate
Population Growth
Limited by Carrying Capacity
Definition:
The number of individuals
the environment can support
over a long period of time
Population Size REGULATION
1. Density Independent Factors: reduce
population regardless of population size
Examples:
 Weather
 Fires
 Floods
Population Size REGULATION
2. Density Dependent Factors:
triggered by increasing
population density
Examples
 Food shortages
 Space limitations
 Waste accumulation
Example of Exponential Growth Phase (JShaped Curve)

Ex. Human Population



Human population increased
relatively slowly until about 1650.
It then doubled in the next two
centuries
It doubled again in the next 80
years.
Our population is now about 7 billion.
 This increases by 80 million/year
 This in an increase of 220,980/day.
 It takes 3 years for the world population to add
the population equivalent of another US.
Example of Exponential Growth Phase (JShaped Curve)
Example of Exponential Growth Phase (JShaped Curve)


How long will it be until
we reach our carrying
capacity? What will
happen then?
What factors increase
our carrying capacity?
 Farming
 Medicines
 Better sanitation
Example of Exponential Growth Phase (JShaped Curve)

What impact does this
stretching our carrying
capacity have on other
species.

Endangers them or
completely wipes them
out.
Example of Exponential Growth Phase (JShaped Curve)

What are some consequences of
human population growth?

Global Warming

Caused by the
increasing burning of
fossil fuels which lead to
the greenhouse effect.

Pollution
 Acid Rain
 Pile up of Waste

Ozone Depletion
The End!!