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Evolution in an Agroecosystem, an Inquiry Lab
(Adapted from OSU Bio101)
Elizabeth L. Kolbe
National Science Foundation Graduate STEM Fellow in K-12 Education
Sugar Creek Watershed K-12 Education Program
The Ohio State University-Ohio Agricultural Research and Development Center
Ohio Learning Standards:
10th Grade Life Sciences, Evolutionary Theory:
13. Explain that the variation of organisms within a species increases the likelihood that at least
some members of a species will survive under gradually changing environmental conditions;
15. Explain how living things interact with biotic and abiotic components of the environment (e.g.,
predation, competition, natural disasters and weather);
20. Recognize that a change in gene frequency (genetic composition) in a population over time
is a foundation of biological evolution;
26. Explain that natural selection provides the following mechanism for evolution; undirected
variation in inherited characteristics exist within every species. These characteristics may
give individuals an advantage or disadvantage compared to others in surviving and
reproducing. The advantaged offspring are more likely to survive and reproduce. Therefore,
the proportion of individuals that have advantageous characteristics will increase. When an
environment changes, the survival value of some inherited characteristics may change.
10th Grade, Using Scientific Inquiry:
2. Present scientific findings using clear language, accurate data, appropriate graphs, tables,
maps and available technology;
4. Draw conclusions from inquiries based on scientific knowledge and principles, the use of logic
and evidence (data) from investigations;
5. Explain how new scientific data can cause any existing scientific explanation to be supported,
revised or rejected;
Learning Objectives:
After this lesson, students should be able to:
1. Recognize evolutionary mechanisms, specifically natural selection and genetic drift, in
action;
2. Describe examples of evolutionary mechanisms in nature;
3. Discuss how evolution affects large and small populations;
4. Discuss the influence of evolution on human populations;
5. Produce accurate bar graphs of population data based on two evolution simulations.
Assessment:
Students will be able to evaluate their learning through:
1. Comparing their population data to others in the class and discussing the trends;
2. Participating in group and class discussion of data analysis, evolutionary terms, and abstract
applications of evolution scenarios.
Materials
For each pair of students:
- 10 dots of 10 colors of construction paper (100 dots total)
- 2 squares of identically patterned cloth (approx 18”x18”)
- one pencil for each group with one end covered in masking tape (sticky side out)
- dixie cup to hold and transport dots
- paper and pencil
For the class:
- 10 different colors of construction paper
- masking tape
- pencils to make “tractor wheels”
- 10 petri dishes to hold paper dots
- hole punchers
- excel spreadsheet set up to enter population data from each group.
- background information on habitat scenario (the agroecosystem)
Lesson Outline
Time (min)
Teaching Method
5
Interest Approach
6
Lab Introduction
24
Lab Activity
3
Term explanation
6
Data discussion
9
Discussion/wrap-up
(total: 51 min)
Instruction & Learning Activity
Why are maps useful?
Walk through the lab
Inquiry lab
Define terms in action
Show class data and discuss evolutionary trends
Discussion of natural selection and genetic drift
Lesson:
Interest Approach: 5 min.
Start class by getting students into tables of 4, and then split into pairs at their table. Groups
of 3 are possible, 5 doesnʼt work so well. The pairs will be important for running the lab, but it is
necessary for them to answer the questions as a group of 4.
Review the concept of an agroecosystem, then talk about how mice and hawks interact in
that agroecosystem (hawks visually hunt for mice). Then talk about how mice and tractors interact
(tractors run over mice). With only this information, you are going to see evolution happen.
Lab Introduction: 6 min.
Walk students through the lab, show them how to use the “tractor” and how to be the “hawk”.
Get them excited about performing these roles! Clarify that the cloth is a habitat, dots are different
color morphs of mice, pencil/tape rollers are tractors, and the person picking up dots is a hawk. The
hawk and the tractor are mortality agents. The mice are a population. These terms can be explained
at the outset, but donʼt go over the evolutionary mechanisms, let them discover them on their own.
Lab Activity: 24 min. (this page should be given to students as lab directions)
How do environments select for characteristics of organisms?
Introduction: organisms display various characters or traits, some of which vary. For example, while all
adult butterflies have six legs, some are dull brown and others are bright orange. Even within a species,
characters may vary. What causes such characters to vary among individuals within populations? Why
does it often seem that some organisms appear particularly well matched to their environment, e.g.,
matching tree bark or other substrate on which they are found? In the exercise we examine forces that
cause characteristics or organisms to change, often in ways that increase their ability to survive and
reproduce in their environment.
Objectives:
1.
To discover mechanisms by which characters within populations change over time.
2.
To discover why organisms seem well matched for life in their environment.
Procedure:
1. Work in groups of four.
2. In this exercise you will play the role of two different kinds of mortality agents on a population of
mice in an Ohio agroecosystem: hawks, which are visual predators, and tree branches, which
slam into the earth, killing large numbers of mice.
3. Individual mice are represented by paper dots which vary in color, i.e., there are different color
morphs within the population.
4. Two members of each group will work as hawks, two will work as branches.
5. Spread the fabric over your lab bench; this represents the habitat upon which you feed (hawks) or
crash into (branches). Each mortality agent will work on its own habitat (piece of cloth)
6. Take 5 mice of each color morph and spread them randomly (total of 50 mice).
7. Begin acting as a mortality agent:
- hawks: use bills (fingers) to pick up individual dots.
- Branches: crash into the habitat indiscriminately.
8. Both hawks and branches will remove 40 of the 50 mice from the habitat.
9. When 10 mice are remaining, “reproduce” the survivors by adding 4 additional mice (dots) for
each survivor dot. You should have 50 mice when you begin your second round of mortality.
10. Repeat the mortality process again. At the end of the second round of mortality, mathematically
repopulate the mice (back to 50, as before).
11. record the final numbers of each color morph for each mortality agent in a table and bring the
data to Liz (or Mr. Miller) at the computer.
12. Make a bar graph with colors of mice along the X-axis and number of mice along the Y-axis for
both habitats. Use appropriate labels on your graph.
13. Sort the mice back into their correct trays.
Questions:
1. What color of mice were killed in the greatest numbers? How does the color of those mice killed
compare with their habitat?
2. What color of mice were killed in the least numbers? How does the color of those mice killed
compare with their habitat?
3. why have some mice survived and others have not?
4. how might results for the branches look after an additional three rounds of mortality? Ten rounds?
5. how might results for the hawks look?
6. Many organisms display a remarkable “match” between their characters (appearance) and their
environment; did these organisms “choose” or “try” to have a certain physical appearance? Why
or why not?
7. What evolutionary mechanism is displayed by the hawk group?
8. By the branch group?
9. Can genetic drift result in organisms poorly adapted to their environment?
10. Do either of these mechanisms operate on human populations?
Term Explanation: 3 min.
Explain to students that they have witnessed evolution by two mechanisms, genetic drift and
natural selection. Define these terms and present a few other examples for each mechanism.
Genetic Drift: the change in the allele frequency in a population due to random chance.
Natural Selection: the non-random change in the allele frequency in a population due to selection
pressure.
Data discussion: 6 min.
Hopefully you have collected all the end population data from the groups, and can show bar
graphs of the class populations after evolution against each “habitat”. The natural selection (hawk)
graph should show that organisms that matched the habitat more often survived and the population
evolved to be more camouflaged. The genetic drift graphs should look random, maybe poorly suited
organisms (color-wise) will survive more often that better camouflaged! Allow the students to
discuss, react, and share how their results fit with the rest of the class.
Evolution discussion and wrap-up: 9 min.
When it seems clear that everyone can discuss, with some level of command, the
terminology and mechanisms, turn the discussion to group answers to #10. Allow students to debate
each other to an extent, but DO provide solid examples of how BOTH mechanisms DO affect human
populations today if no one else offers it first. You should make sure the students have clearly heard
that evolution is happening in human populations. This is also a good opportunity to begin talking
about the other types of selection (artificial, sexual), and to get them interested in more ecological
examples and possible mortality agents.
Allow groups to clean up their answers to the lab questions after the discussion, collect during the
next class.