Biology Lessons Part 2: Population Biology

Lesson 2.8: How Do Populations Change Over Time? Knowledge Mapping Exercise

Grade Level	Prospective and Practicing K-8 Teachers; may be adapted for use in elementary classes.
Time	Approximately 1 hour.
Objectives	Once you have completed these exercises you should be able to:
	1.	Describe protective coloration.
	2.	Distinguish between microevolution and macroevolution.
	3.	Distinguish between sexual selection and survivability selection.
	4.	Construct nets from text.
	5.	Merge nets.
Exercise 1	Changes in Traits in a Relatively Few Generations: Natural Selection and MicroEvolution
Introduction	1.	Consider these four observations of guppies which have been made in the wild by John Endler at Princeton (1996), in various pools and streams in south America (Venezuela, Margarita Island, Trinidad, and Tobago). The subject is a fish called the guppy and the trait is its spotted coloration which is inherited.
	2.	In pools where there are no predators, male guppies are very brightly colored. They have black, blue, red, yellow, green and irridescent spots. Endler observed that bright colors attract females and increase the chances of mating and reproduction. The gaudier the male, the better his sex life.
	3.	In pools where predators abound, male guppies have smaller, paler spots and they blend into the background better. Pale males are caught by predators less frequently than bright-colored males.
	4.	Guppy predators range from the most dangerous, a cichlid fish which eats about three guppies per hour, to the least dangerous, a fish called Rivulus hartii, which eats about one guppy every five hours. The more aggressive the guppies' enemies, the smaller and fainter the guppies' spots.
	5.	In pools where the predators are prawns, male guppies have bright red spots. Prawns are generally attracted by bright colors but are red-color-blind.
Questions	6.	Which of these observations provide evidence of protective coloration?
	7.	In the guppies, are the selective effects of sexual selection and survivability reinforcing one another or counter-acting one another? Sexual selection is the attractiveness of an individual to mates and its ability to reproduce. Survivability is the ability, in this case, to avoid predators and thus survive.
	8.	Supposing you were to take about 200 pale-colored male and female guppies from a stream containing guppy predators and place them in a safe stream where there are no guppy predators. You come back and look at the population one year later (about 15 generations later). What would you expect to see?
	9.	One way to think of natural selection is as follows.
	10.	Construct a small semantic network to represent the information you learned in this knowledge mapping lesson.
	11.	Now construct a net to represent the simulation you performed with beak size and shape. Include both the specific beak sizes, shapes and outcomes from the experiment, and a conceptual overview of what happened.
	12.	Now merge your two nets together and review and revise as necessary. Your goal is to build a coherent conceptual picture of evolution illustrated by data from Endler's experiments and from your simulation.
	13.	Distinguish between sexual selection and survivability selection.
	14.	Macroevolution refers to the large scale changes that have occurred in life forms on earth and that are studied through the fossil record. Distinguish between macroevolution and micro-evolution.
	15.	How do the short-term changes in populations occur?