Population: A group of organisms of the same
species, living together and interbreeding.
• Populations usually are too large or spread
out to study every individual.
• Ecologists use graphs to organize
information about populations.
• The human population has changed
drastically in the history of mankind.
• Populations affect and are affected by their
environment and the other organisms in it.
Population Growth
• Growth curve: graph showing the number of
individuals in a population over time.
• Biotic Potential: rate at which a population
will grow if all individuals survive and
reproduce at maximum capacity.
Linear Growth
Linear Growth:
Growth that
occurs in a
straight line.
(This generally
doesn’t happen
in nature.)
Exponential Growth of Cells
Exponential Growth:
Growth at an ever-increasing rate; calculated
using exponents. (The population has reached
biotic potential)
J-shaped curve
Shows 2 phases:
1.Lag phase: little or
no increase in
population.
2.Exponential phase:
period of
exponential growth.
(Can you label these
on the graph?)
http://www.biologycorner.com/bio4/notes/popgrowth.php
S-shaped Curve
Depicts limits on
population due to
environmental factors.
Carrying capacity:
maximum number of
individuals that an
ecosystem is capable of
supporting.
(Label lag phase,
exponential phase and
carrying capacity.)
Limiting Factors:
Variables in the
environment that limit
the growth rate.
• Food
• Disease
• Forest Fires
• Dutch Elm Disease
• Kaibab deer
• FIV virus: Evolutionary Arms Race- Wildcats
Human Population Growth
Demographic Trends
Video Clip: Population Explosion
Demography: the study of human population growth
characteristics.
Why is the human population so successful?
1. Better Sanitation.
2. Increased food productions (agriculture).
3. Control of disease. (medical technology)
Growth Rate
Birth Rate: the number of individuals
being born into a population.
Death Rate: The number of
individuals dying from a population.
The difference between the birth rate
and death rate is the growth rate.
population
equilibrium
• a situation in which the population stays at the
same level, because the number of deaths is
the same as the number of births
The Population of the World
The solid line in this graph shows estimates
of the size of the world's population over the
last two millennia. The estimates from 1800
to 1991 are based on more accurate data than
those before.
The dotted line shows what would happen if
exponential growth continued to the year
2100.
As you can see, the world's population has
been growing exponentially (except during
the years of the black death). How long will
it continue to do so? (Since the graph was
drawn, the world's population has reached
6.5 billion; that is, in 2007 we are still on
course.) But can it continue indefinitely?
Surely not.
Influenza and
Pneumonia
Pandemic
Excess Annual Death Rates from Influenza and Pneumonia: 1887-1921
Age Structure
Graph that refers to portions of
populations at different age levels.
http://www.uwlax.edu/faculty/skala/Age-Structure.htm
What does this graph tell us about the
population?
Is this population stable?
Yes?
http://www.uwlax.edu/faculty/skala/Age-Structure.htm
How do we know?
There are the same number of Prereproductive and post-reproductive
individuals.
http://www.uwlax.edu/faculty/skala/Age-Structure.htm
In 1980, does country X exhibit an age
structure more typical of a developing
nation or an industrialized nation?
Explain.
What might account for the age structure
predicted for the year 2080?