Population Dynamics
EQ: How do populations interact with
the environment?
What is a population and how can it
affect the ecosystem?
What is a
population?
Populations are defined as
• A group of individuals of the same species that
live in the same geographic area at the same
time.
Characteristics of Populations
•
•
•
•
Density
Birth and death rates
Growth rates
Age structure
Population density is defined as:
• Number of individuals of a
species within a given area
• Usually referred to in terms of
human populations
– For example, Canada's
population of 33 million,
divided by the land area of
3,559,294 square miles
• Can you do the math??
9.17 people per square
mile in Canada
• However,
population density
also defines all
species!!!
Population Density
How might population growth affect
the density of a population?
As population size
increases, so does the
population density.
• As population size
decreases, so does the
population density.
Biodiversity and Populations…
• The variety of life on Earth, its biological
diversity is commonly referred to as
biodiversity.
– The number of species of plants, animals, and
microorganisms, the enormous diversity of genes in
these species, the different ecosystems on the planet,
such as deserts, rainforests and coral reefs are all part of
a biologically diverse Earth.
We will get more into
Biodiversity and resources in
the next unit…
Why Is Biodiversity Important?
• Biodiversity boosts ecosystem productivity where
each species, no matter how small, all have an
important role to play.
• For example,
– A larger number of plant species means a greater variety
of crops
– Greater species diversity ensures natural sustainability
for all life forms
– Healthy ecosystems can better withstand and recover
from a variety of disasters, such as hurricanes.
What is carrying capacity?
• Carrying capacity refers
to the largest
population size a given
environment can
sustain/support.
• What happened to the
deer population
between 1960 – 1966?
What is growth rate?
• Growth rate refers to
how the population
changes in size during
a specific period of
time.
• Why might this graph
show a decline in overall
world growth rate by
2050?
Types of Growth
• Exponential Growth – when a
population grows by a fixed percentage
each year. Changes in the population
size are noted by population growth
curves.
Types of Growth, cont
• Fluctuating growth in Nature • Rise and crash growth ratepopulations grow rapidly and
– fluctuates around carrying
resources are used quickly, thus
capacity.
their populations crash. Or there
is a sudden negative influence
upon the population.
Life history Patterns
• Are developed when scientists study the
factor that determines population growth –
the reproductive pattern is called a life history
pattern
Rapid vs. Slow Life Histories
Rapid
• Are common among
organisms from changeable
or unpredictable
envrionments
Slow
• Common among organisms
that live in a more stable
environment
• Generally organims have a
smaller body size, mature
rapidly, reproduce early,
and have a short life span
• Larger body size, reproduce
and mature slowly, and are
long lived.
Limiting factors to populations
• A limiting factor is a biotic or abiotic factor
that influences the survival rate (biotic
potential) of populations. There are two types:
– Density dependent
– Density independent
Density Dependent
• Resources are
dependent on how
large the population is.
In the graph to the left,
moose and wolves are
dependent on each other.
As moose increase, so do
wolves. However, if wolves
decrease, what happens to
moose?
What other density
dependent factors can you
think of?
Density Independent factors
• Limiting factor whose
influence is not affected by
populations
• If you look at the graph to
the left, what caused the
sudden decline in Aphid
populations? When did this
decline happen?
• What other density
independent factors can
you think of?
Book Work
• P.99 Q’s 1-5
• Worksheet on Biomes
Demography:
the study of human population size,
density, distribution, movement and
growth rates
EQ: How do humans affect the
ecosystems?
WARM UP: How do we study human
populations and their affect on an
ecosystem?
A very brief activity…
Human Population circle
Population Circle Discussion
• What did you observe about how our
population changed over time?
• How long did it take before the first person
moved into the circle?
• Towards the end of the simulation how long
did it take to add 250 million people onto
Earth?
• What will happen if we continue to grow at
this rate?
Population Growth and The
Distribution of Humans.
• http://www.youtube.com/watch?v=9_9SutNmfFk
• After watching the video – answer the questions.
• 1. Around what year did you begin to notice an increase in
population growth?
• 2. What historical events, scientific advances or other
changes may have contributed to a population increase?
• 3. What historical events may have contributed to a
population decrease?
• 4. How might historical references help to explain changes
and trends in population?
Besides limiting factors, what else
influences populations?
• Birth rates
• Death rates
• Immigration or Emigration. (Do you know the
difference?)
• Migrations
Birth Rates
• Rate at which individuals are born is called
natality.
Death rates
• Death rate is the rate at which individuals die
which is called mortality.
Immigration
• Arrival of individuals from outside a given
area.
Emigration
• A departure of individuals from a given area.
The population of Ireland 1700-2000
numbers in millions
Migrations
• Seasonal movement into and out of an area.
Paperclip Creatures.
• You will get a container of 50 paperclips and a stop watch.
• You will need to decide on the following:
– You need two storks
– You need two grim reapers
• Count the total number of unconnected paperclips (if they are
connected, unconnect them.) This number should be 0!
• You will have 30 sec to connect as many paperclips as possible if you are
a stork. However, the grim reaper will be unconnecting the paperclips as
they are assembled.
• Count the number of “living” paperclips (those that are together). Count
the number of unconnected paper clips as well.
• Repeat until you have completed 5 years total. Record your data.
Paperclip Creatures.
• We will tell you who is a stork and who is a
grim reaper. Repeat the activity until you have
completed 5 years total. Be sure to record all
of your data.
Paperclip Creatures.
• Analysis Questions :
1. Make a graph of the total number of paperclip
creatures versus the year for both runs. Put time on
the x-axis.
2. Write a paragraph (3-5 sentences) that describes the
relationship between time and population size.
3. What would your graph look like if there were more
storks? Grim reapers? Explain your thinking.
4. How do births and deaths affect the size of a
population?
How do we calculate Population Growth?
• Population growth is measured by
Birthrate-deathrate= population growth.
• A more complete growth model would include
immigration and emigration, but these
numbers are not always accurate.
How do we calculate population
growth rate?
• Population growth is calculated using the
following equation:
• (Current year population-Previous year
population)/previous year population x100
• For example the current deer population is 36,
10 years ago it was only 5.
• 36-5= 31/5=6.2 x 100=620%
Year
National Population
2010
308,000,000
2000
281,000,000
1990
249,000,000
1980
227,000,000
1970
205,000,000
1960
181,000,000
1950
152,000,000
TRY IT!
• (Current year populationPrevious year
population)/previous year
population x100
• Find the population growth rate between 1990
and 2000. 13% PGR
• Then find the population growth rate between
2000 and 2010. 9.6% PGR
Why might the population growth rate
be lower between 2000-2010 than
between 1990-2000?
Warm UP: What are the
characteristics that affect
populations?
Doubling Time
• Is the time needed for a population to
double in size.
• Complete p. 102 Minilab Procedure and
Q’s 1-2 from the book.
Mini Lab Answers
Data Graph
Geographic Region Annual Percent of
Growth Rate
Doubling Time
A
B
C
D
2.4
1.7
1.4
0.5
29.2
41.2
50
140
E
-0.1
Is decreasing and
will not double
1. A; D
2. High potential for disease, problem with
waste disposal, lack of space and/or water
Age structures:
refers to the proportions of the
population that are in different age
levels.
Rapid Growth Age Structure
• Rapidly growing
countries have age
structures with a wide
base because a large
percentage of the
population is made up
of children and
teenagers.
Slow Growth Age Structures
• This age structure
diagram predicts a slow
but steady growth rate
for the near future.
Decline in Growth
• This graph shows that
the population is on the
decline because there
will be less people
reproducing than
people who have
already reproduced.
Age Structure Diagrams explained…
• http://legacy.hopkinsville.kctcs.edu/Sitecore/instruc
tors/JasonArnold/New%20VLI/Module%204/Mod4PartA/age_
structure_v2.swf
WORK!
• Be sure to turn in the paperclip
creatures graph and analysis
questions!
• P. 103 Q’s 2-5
• Human Population worksheet