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Population Dynamics
Quickie vocab review
Population
group of individuals of the same species living in the same
geographic area
Carrying capacity
maximum number of individuals of a species that the ecosystem
can support
Limiting Factors
Factors that regulate population using multiple
criteria (internal vs. external, abiotic vs. biotic,
density-dependent vs. density independent)
Density-dependent factors: factors that inhibit
the overgrowth of a pop’n when numbers of the
pop’n are large
Density-independent factors: factors that affect
population growth but have nothing to do with
density
DD Factor, or DI Factor?
food
Water supply
parasitism
temperature
predation
floods
storms
fires
earthquakes
amount of sunlight
disease
weather
competition
space
Examples
In most freshwater lakes algal productivity is
limited by the availability of inorganic
phosphorus in the form of the ion phosphate.
The production of grass in a field can be limited
by nutrients even if there is enough sunlight.
Population Growth Curves
Nearly all populations
will grow exponentially
as long as there are
resources available
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookpopecol.html
The J-curve occurs when
there is no limit to
population size
Population Growth Curves
The S-curve, or
logistic curve, shows
the effects of a
limiting factor on
population
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookpopecol.html
Biozone p. 58
points for biozone: /10
Add axes to this sketched population curve, and
identify and give a definition for the lag phase
Laptops ready?
1. Use Excel to plot the data shown on p. 59 of
Biozone, and then answer the questions in
your book. Show me your Excel plot (with a
title, and labeled axis) for credit.
2. You may consult with a partner for the
questions, but you must do the Excel graph
on your own. You should create the Excel
data by using a formula.
3. Be ready to discuss your answers to the
questions when finished.
Visualizing Effects of Birth Rate on Population
Growth
Predict: What type of growth would a population show
if it has a constant birth rate and is not limited by food
or disease?
_____________________
Sketch a graph of what you would predict for the above
situation, and label your axes
Go to http://www.otherwise.com/population/exponent.html
and click on “run applet” under the exponential growth section
1.
2.
3.
4.
5.
Set the birth rate to 1.2 and press “run,” and “stop” the
simulation when the 25th generation has been born. Sketch the
graph on both sets of axes on the next slide (give minimums
and maximums but no scale needed), and label it. LABEL AXES
FIRST.
On the set of axes for Chart 1, draw a prediction of how the
graph would look if you changed the birth rate to 1.5, and label
your prediction clearly.
Change the rate to 1.5 and click “reset,” and then “run” the
simulation for 25 generations. Observe graph and then sketch it
on the axes for Chart 2. Label your plot clearly.
On the same axis as before, predict what the graph might look
like if the birth rate fell to 0.8 and draw your prediction. (label)
Now test out your prediction. Draw the actual graph on Chart 2.
Chart 1. Set of graph sketches
for predictions at birth rate =
1.5, 1.2, and 0.8
Chart 2. Actual sketches at
birth rate = 1.5, 1.2, and 0.8
Points:
/ 15
Adding carrying capacity to the simulation
Scroll down to logistic growth, then “run applet”
1.Before running the applet, sketch a prediction of the
expected shape of this graph on Chart 3.
2.Run the applet for 30-40 generations at each of the
following sets of parameters, hitting reset in between:
b. rate: 1.8
carrying cap.: 1000
b. rate: 2.0
carrying cap.: 1000
b. rate: 3.0
carrying cap.:1000
Sketch all three of the situations on Chart 4. Label all
axes appropriately before moving on.
ALS1
Slide 13
ALS1
Stop in between here!
Alyssa Schultheis, 2/4/2009
Chart 3. Sketch of overall
expected shape when carrying
capacity introduced
Chart 4. Actual sketches at birth
rate = 1.8, 2.0, 3.0, and carrying
capacity constant at 1000
Points:
/ 10
Choose one of the birth rates used previously, and run
for three different carrying capacities. Sketch results and
label clearly.
Points:
/8
Quiz Review
R-strategists vs. K-strategists
NOTE: these are idealized categories and many organisms occupy a place on the continuum between
these two types
R-strategists
prefer survival at low population density,
near the lag phase of the curve where
biotic potential (r) is high
can develop rapidly and produce a large #
of offspring (adapted to exp. Increases)
Ex: American oyster, house mouse, pioneer
species– wide dispersal in disturbed habitats
R-strategists vs. K-strategists
K-strategists
survive well at or near carrying capacity (K)
usually found in stable habitats
long life spans (ex: elephant and tortoise)
take good care of young and infant
mortality tends to be low
Survivorship Curves
I: high
survivorship of
young, live to old
age
II: relatively
constant death
rate (due to
hunting/disease)
III: high birth
rates, young die
early
Carrying Capacity Scenarios
Determining Carrying Capacity of
Non-humans
Maximum population of a species that can
survive indefinitely in a given environment
Depends on:
-conditions and resources available
-consumption habits of species
Issues with calculating Human K
Human K and the IPAT equation
“If there are too many people, even the most wisely managed
technology will not keep the environment from becoming
overstressed.” Environmentalists Paul Ehrlich and John Holdren
(1972)- Journal of Industrial Ecology, 2001
http://www.buddycom.com/ecol/Brainfood/EcoLaws.html
http://belfercenter.ksg.harvard.edu/files/
John%20Holdren%20headshot%20300
%20dpi.jpg
The IPAT equation:
I = PAT
I = environmental impact
P = population, A = affluence, T = technology
•I can be expressed in terms of resource
depletion or waste accumulation
•A refers to level of consumption of a population
• T refers to processes used to obtain resources and
turn them into useful goods and wastes
Estimates of K for humans range from ½ billion to 300
billion!
If the variables are considered
separately…
I = PAT
What would happen to I if P, A, T decrease?
What would happen to I if P, A, T increase?
If impact and population held constant, how does A
change with P?
Even though the IPAT equation assumes independence
of the variables…
Not so in the real world!
For ex., in the 1980s, slower pop’n growth
appeared to facilitate faster consumption
growth in developing countries
Also, higher income levels tend to improve
environmental technology
Ehrlich used the IPAT formula to show that
population growth was the dominant factor in
environmental damage.
That darn exponential
population growth!!
In reality, different elements have been most
important at different historical times
Examples of Applications of IPAT equation
Increase in arable land in many parts of Africa up to
~1980 and deforestation that went with it was due
mainly to pop’n growth (there was little rise in
consumption of agricultural products/person and little
improvements in yield)
By contrast, the dramatic rise in human output
of CFCs from the 1940s on was due to
introduction of a new technology
Many economists argue…
…that human carrying capacity can be expanded
continuously through technological innovation.
Ex: if we learn to use energy and material 2x as effic.,
we can doub. the pop’n or use of E w/o necess.
increasing load on env.
To compensate for future population growth
deemed necessary, though, it is suggested that
efficiency would have to be raised by a factor of
4 to 10 to remain within global carrying capacity
Questions to Ponder with a Partner
Why do you agree/disagree with the statement that
human carrying capacity can be expanded continuously
through technological innovation?
Estimates of human carrying capacity vary from 2.5 bill.
to 40 billion. Why do the estimates vary so widely?
Identify at least 4 variables that can be considered
when using models to determine human carrying
capacity, and explain how these variables can affect K.
What value systems are involved in the consideration of
the variables you mentioned for the previous question?