Download Natural Selection

Population Dynamics Lesson Plan
Information about the Lesson
Topic: Natural Selection
Abstract
This is the first lesson on the topic of natural selection. It deals with the different way in which
populations change due to multiple factors, which in turn is the driving force of evolution. It will be
followed by lessons on speciation, genetic biodiversity and phylogenetic relationships. Prior to this
students studied genes, pedigrees and the cell cycle.
Lesson Goals
State Objectives
B5.1a Summarize the major concepts of natural selection (differential survival, and reproduction of
chance inherited variants, depending on environmental conditions).
B5.1b Describe how natural selection provides a mechanism for evolution
B5.1e Explain how natural selection leads to organisms that are well suited for the environment
(differential survival and reproduction of chance inherited variants, depending upon environmental
conditions).
B5.3a Explain how natural selection acts on individuals, but it is populations that evolve. Relate
genetic mutations and genetic variety produced by sexual reproduction to diversity within a given
population.
Big Ideas
Natural Selection is the gradual, nonrandom process by which biological traits are selected for
in a population as a function of differential reproduction. It is a key mechanism of evolution.
Natural selection acts on the phenotype, or the observable characteristics of an organism, but
the genetic basis of any phenotype that gives a reproductive advantage will become more common in
a population. Over time, this process can result in populations that specialize for particular ecological
niches and may eventually result in the emergence of new species.
Students' Prior Knowledge
Students may think that natural selection acts on an individual instead of a population and that
it is exclusive; not effected by multiple factors. They may also confuse natural selection with
adaptation.
Observations/Examples/Data
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Darwin's Finches
Pepper Moth
Peacocks
Humans
Classroom Activity
Materials
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Grey, foam divet mat
Four colors of beans
Foam cups
“mouth parts” (forcep, hand, fork, spoon, knife)
Activities
Introduction (10 min)
Establish a problem—You are a park manager at a national forest and are tasked with perserving the
population of the different species in the genus Utensilitis. You duties will include determining the
type of prey that this genus thrives on and how that changes over the course of generations.
Partner up—Discuss what you think an example of natural selection is and what makes it natural
selection. Share with class.
Main Teaching Activities (40 min)
Model—On the job training
 Explain examples of Darwin's finches and the pepper moth
 Diagram simple example of natural selection; explain generations and population variance
◦ Circle does well in wet climate, square does well in dry, triangle does well in both
◦ Show changes in generations and population after certain seasons
Coach—Work in groups of 4 to 5
 Each student will be assigned to one of the structural feeding variation groups; that is,
predators which feed using forceps, hand, spoon, fork, or knife. These variations represent
genetically fixed differences in the population. All individuals have identical mouths (cups).
 50 beans of each color (200 beans total) will be spread out in an area representing the habitat
of these organisms. Mix the colors well (no patches of just one color beans)
 Begin hunting when the instructor says to begin and continue until you are told to stop. The
prey (beans) must be picked up with the feeding apparatus (forceps, hand, spoon, fork, or
knife) and placed in the mouth (cup, please don't really eat the beans). No scraping or pushing
of the prey into the mouth is allowed. You must hold the bottom of the cup flat against the
table. You may, however, dash in and pick up any prey being pursued by another predator.
Don't hesitate to intrude…any hungry natural predator would "go for it!"
 When told to stop hunting, count and record the number of each type of prey you captured
(tables are attached). We will total the "kills" by type of feeding apparatus for each type of
prey. This will allow us to see which predators were most successful (measured by success in
capturing prey) and which prey were most successful (measured by NOT being captured).
 The predator groups will be reconstructed for the next generation. Predator types which
capture fewer prey than others are not successful hunters and natural selection might remove
them from the population. After two generations the least successful predator type will be
considered extinct. After the third generation the least successful predator (of the remaining
types) will again be considered extinct. Students that had those feeding apparatus will be
assigned to other groups and will represent the offspring of the successful predator types.
 After each period of hunting the prey remaining in the prey population (those not captured)
will be doubled to represent reproduction. The additional beans of each color will be added to
the remaining population in the habitat.
 After each generation and the restructuring of the predator and prey populations, predators
will again be allowed to hunt for a specified time period and the procedures will be repeated.
This will be done for four generations.
 Data tables (attached) will be filled out as we work through the exercise.
Conclusion (5 min)
Fade—In order to finish your job and report out to the government you must answer these questions
in your report. You may work in a group and finish for homework
1. Which prey variation (bean color) appears to be best adapted to the environment? Explain, based
on your data, why that group is considered to be best adapted. Explain, in the "real world" (that is the
world of beans) why this group is best adapted.
2. Which prey variation appears to be least adapted to the environment? Again, explain, based on
your data, why that group is considered to be least adapted.
3. Which predator variation ("mouth" type) appears to be best adapted to feeding on this prey
population? Explain, based on your data, why that group is considered to be best adapted.
4. Which predator variation appears to be least adapted to feeding on this prey population? Explain,
based on your data, why that group is considered to be least adapted.
5. Write a statement explaining natural selection and how this simulation demonstrates the role of
natural selection in populations (both predator and prey).