Ecology Group: Population Growth
Context: Group Members and Their Students;
Design Scalable Teaching Unit
Learning Goal: Understand and interpret population
growth equations and graphs.
Learning Outcomes:
Given data, students should be able to
1. plot data, calculate and interpret r; and
2. forecast future population size.
Ecology Group: Population Growth
Assessment:
1. Gauge prior knowledge
o
Multiple Choice Questions (clickers)
o
Concept Mapping
o
Terminology Challenge – Card Game in Groups
2. Calculate Instantaneous Growth Rate; Predict Population Size
o Chalk-Talk
o Formative assessment (MCQs, clickers)
3. Group Activity: Physical Model, Growth of Bacterial Population
o
Addressing Diversity
4. Post-Group Activity Formative Assessment
What Do You Know?
A _______ is defined as a group of individuals
of a single species that occupies the same
general area.
A. population
B. community
C. ecosystem
D. biome
What Do You Know?
The size of the human population has not
changed in the last 200 years.
A. True
B. False
What Do You Know?
The maximum number of individuals a habitat
can support indefinitely is called the _______.
A. population fitness
B. community size
C. carrying capacity
D. reproductive potential
What Do You Know?
log10(100)= _______.
A.
0.01
B.
10
C.
0.1
D.
2
Chalk Talk I
Explain exponential
Chalk Talk I
N = population
size
B = birth rate
D = death rate
b = per capita
birth rate
d = per capita
death rate
r=
instantaneous
growth rate
N0 = initial
population size
Nt = population
size at time t
Experimental Design
5 cups containing skittles
Each skittle = an individual Meningococcal skittlus
Cup = time of sampling M. skittlus bacteria.
Step I
Is the population size increasing, decreasing, or
stable?
Count the number of bacteria per sampling period
– population size (N)
Graph your 5 data points using N and t as your
coordinates (Is N on the x or y axis? t?) *
How would you predict population size at the sixth
sampling period (N6)?
Chalk talk II
Step II
Plot the data on semilog paper.
Is the population increasing, declining, or staying
stable?
How would you estimate instantaneous growth rate
(r)?
How would you estimate population size at time zero
(N0) ?
Check of the Facts – Part I
If r is positive, the population should:
a. Grow.
b. Shrink.
c. Stay the Same.
d. The dog ate my homework.
Check of the Facts – Part II
If r is positive, the population’s:
a. Deaths = Births.
b. Deaths > Births.
c. Deaths < Births.
d. I love Brussels sprout.
What Do You Think?
The type of growth illustrated by the global human
population during the past 2,000 years is
_______.
A. exponential
C. linear
B. logistic
D. extra-exponential
Future Directions
Explain curves graphically, written (freshman, nonmajors),
equations (seniors)
Incorporate software packages (MS Excel, R)
Calculate N6 given logNt = logN0 + rt
Add stochasticity to data (biological variation)
Add terms for:
Logistic growth – includes K
Interspecific competition
Predator prey
Phenotype confers fitness advantage – evolution
Radioactive decay and age dating
Possible Summative Assessment Questions
Calculate the population size at year seven of a lion
population with an initial population size of 20 and
an intrinsic growth rate of 0.1 (rounded to the
nearest whole number).
1) 25
2) 30
3) 35
4) 40
More
Which r value best fits the curve in the figure?
1) -0.25
2) -0.7
3) 0.25
4) 0.7
Summative Assessment
Q: The endangered purple falcon, which is endemic to
your state, has a current population size of 10
individuals in 2012. The population growth rate of
the falcon over the past decade has been 0.05.
Delisting of the falcon from the Endangered
Species List can occur when the population
reaches 1000 individuals. Using the densityindependent population growth equation, when
should the falcon be delisted?
A: 46 years [question can be answered without a
calculator if need be.]
Logistic Growth Assessment
In the figure above, the term (K- N)/K
A. is greatest when N is large.
B. becomes smaller as N approaches K.
C. becomes larger as N approaches K.
D. is the carrying capacity for a population.
More questions.
Q:Explain the differences between exponential and
logistic growth. What are the differences with
regard to growth rates over time? What drives
those differences (what is different about their
habitats)? What is the difference in their differential
equations? What is the difference in the shape of
the curves? Which is most commonly found in
nature?