Transcript Document

Development of a diagnostic question cluster and post-assessment
of college student understanding about population dynamics
Miranda A. Kearney and Nancy E. Stamp
Biological Sciences, Binghamton University - State University of New York, Binghamton, NY
Post-assessment
Pre-assessment
Iteration #1 (N=271 introductory biology students)
Figure 1: Gause’s Experiments
After a lecture and reading but
prior to a class activity on the subject
of population dynamics, students were
asked questions based on data from
Gause’s Paramecium experiments.
Initially, we used a common textbook
representation of that data (Fig. 1).
This classic set of experiments nicely
illustrates:
1. Phases in population growth
(exponential, then effects of
limiting factors resulting in
slowed growth that eventually
plateaus)
2. Support for Lotka-Volterra
logistic model
3. Different species have different
carrying capacities (K)
4. An example of intraspecific and
interspecific competition
Sample Questions & Responses:
A. How do you explain that these two species can coexist in a pond?
• 35% said: Two species cannot coexist because Fig. 1C shows that they are
unable to live in the same environment
• 20% - Ponds have more space
• 17% - Ponds are larger and contain multiple exploitable niches
• 13% - There is more food available in the pond
• 9% - Pond have more food and are larger
B. If daily samples were taken from a pond over a 2.5-week period, what do you
think the population growth patterns would look like?
Iteration #2 (N=24)
We provided more detail about the Gause experiments and asked
questions only about Figure 1C. We added another question that included a
different graph with actual data points. We asked which figure was a better
illustration of Gause’s results and why.
Iteration #1 (N=274)
After a class activity, we administered a post-assessment to determine if the activity
helped students overcome misconceptions about population dynamics. We used
estimates of linked prey and predator populations for the following reasons:
1. This data set is used in many textbooks as an example of cycles in population size
that can be readily explained
2. The snowshoe hare is a critical species in boreal ecosystems; its loss would result
in loss of predator species and a significantly altered plant community (Krebs et
al. 2001)
3. Study of the hare-lynx relationship has helped ecologists understand how time
lags in both direct and indirect effects predation contribute to population cycles
Figure 3: Hare and lynx data from historic pelt records of the Hudson’s Bay Company
Sample Questions & Responses:
A.What is the carrying capacity for the hare population? For the lynx population?
• 93% said: It is the maximum peak on the graph (i. e., approx. 150,000
hares and 80,000 lynx)
• 4% - It is an average across the 100-year time scale of the graph (i.e.,
approx.70,000 hare and 40,000 lynx)
• Only one student responded that it changed with resources
B.What determines the carrying capacity for the hare population?
• 28% said: Predation (or more specifically the number of lynx)
• 28% - Other or blank (many said carrying capacity was determined by the
“peak of the graph”)
• 22% - Available food or resources
• 18% - Combination of available resources and number of lynx
• 4% - Space
C.What causes the cyclical pattern seen in the graph?
• 47% said: Prey population increases causing the predator population to
increase. This causes the prey population to decrease. Soon after, the predator
population also begins to decrease.
• 24% - The Lotka-Volterra Model
• 22% - Other or blank
• 7% - Described the lynx and hare interaction in detail addressing food
supply limits and population dynamics
Textbook analysis
92% Preferred graph
with data points (fig. 2)
8% Preferred smooth
graph (fig. 1)
•66% of 12 recent textbooks (5 introductory biology and 7 ecology) used
Gause’s Paramecium experiments to illustrate logistic growth
• But only one used the graphs well
• 92% used hare-lynx pelt data
• Only 58% used subsequent research to explore causes of the cycles
• Definitions of carrying capacity varied within and among textbooks
Figure 2: From Gause’s The Struggle for Existence (1934)
Best Student Description: “This figure is a better illustration of Gause’s
results because it is logical that both species would show a decline in
population density when in competition with one another. Even if P. aurelia
vastly out-competes P. caudatum as long as P. caudatum has not gone
extinct, it should still be showing reduced numbers from those of the
species by itself.”
Conclusion
Typical presentations of concepts, data
and application fall far short of
objective.