Changing Populations- A Lesson in Adaptations (Audrey Benson)

Tri-Finger- Tape the middle and pinky fingers together. Next, tape the middle and index fingers together leaving the thumb free.

3. The instructor will place each individual next to a pile of "food" (this will first be the beans, then the rice). Each individual will hold a paper bowl with their untaped hand and wait for the signal

4. When the instructor shouts "GO!" each individual will have 10 seconds to collect as many pieces of food and will place them into their bowl. Each bean or grain of rice should be collected ONE AT A TIME. Individuals may only use their taped hands to collect food.

5. After 10 seconds has passed, the instructor will shout "STOP!" Only beans and rice in the bowl count toward the individual's total.

6. Each individual must collect 5 pieces of food in order to survive and reproduce.

If an individual DID NOT collect 5 pieces of food, he or she "dies" and must sit back down.

If an individual DID collect 5 pieces of food, he or she can "reproduce" by tagging another classmate. The "offspring" will assume the same hand shape for the next round.

7. The instructor will ask for all individuals who collected 5 pieces of food to raise their hand and will record the surviving number on a data table. Those who did not collect enough food must sit back down. This is done for three rounds with individuals picking up beans, and is then repeated for three more rounds with individuals picking up rice.

LINK TO CHART

Bean Environment

Rice Environment

Student prior knowledge: Students should be able to define an adaptation as "a trait with a current functional role in the life of an organism that is maintained and evolved by means of natural selection." They should also understand Mendelian genetics and how traits are inherited.

Explanation: Give a thorough explanation of the experiment or demonstration. Your explanation should be written to give your fellow teachers a solid understanding and include greater detail than what you might provide for your secondary students. Make certain to include equations whenever pertinent.

Organisms with the best adaptations for the environment tend to survive and reproduce, making their heritable traits the most prolific in the population. When gene frequency in a population changes, microevolution is taking place and can ultimately lead to big changes in these species. When environmental changes occur, this can impact an organism's survival and ability to reproduce, ultimately leading to changes in the species that live there. This can occur in a variety of ways- species may expand, new species may emerge as populations diverge under different conditions, and some species may decline or become extinct.

This activity demonstrates how environmental changes affect traits in populations. Each hand-shape is a trait: Thumbless, Di-Finger, and Tri-Finger. Individuals that have traits making it difficult to pick up the beans and rice won't be able to acquire as much food, won't reproduce, and will die. When the population is reexamined, the these traits should be less prolific than those that are better suited to picking up the beans and rice.

Questions & Answers:

1. Explain how speciation could occur in these populations after many generations.

The original population consisted of an equal number of Thumbless, Di-Finger, and Tri-Finger individuals. If individuals with the Thumbless trait are unable to gather enough food to survive and reproduce, this trait may vanish from the population, leaving only Di-Fingered and Tri-Fingered individuals. Intraspecies competition between remaining individuals may eventually lead to resource partitioning where Di-Fingers tend to specialize in gathering beans and Tri-Fingers tend to specialize in gathering rice. These populations would tend to keep to themselves and breed with each other, eventually leading to two separate species.

2.. Give an example of an environmental change that might affect the species that live there.

A population of animals lives on the grassland, feeding on shrubs and trees. These animals vary in height, ranging from three to ten feet tall. A fire suddenly burns all of the shrubs, but the trees have fire-resistant bark and manage to survive. The shorter animals now have no foodsource and are not tall enough to gather leaves from the trees. This environmental change could lead to the die-out of all of the shorter animals, leaving only the tall ones. These tall animals would mate with each other and continue to have tall offspring, leading to a taller population. If fires continue to keep the shrubs from growing in this area, the species may eventually consist of only tall individuals.

3. The endangered Tidewater Goby (Eucyclogobius newberryi), native only to the California coast from Del Norte County to San Diego County, lives exclusively in coastal brackish water habitats, including streams, estuaries, and lagoons. If 95% of these coastal areas are cleared for human development, what would you hypothesize could happen to the Tidewater Goby?

The Tidewater Goby is extremely specialized and needs brackish habitats in order to survive. If humans clear out all of these areas, the Tidewater Goby will no longer be able to survive and could go extinct.

Applications to Everyday Life: Explain (don't just list) three instances where this principle can be used to explain other phenomenon.

1. Darwin's Finches are a great representation of the principle of environmental adaptations of a species. These birds share a common ancestor but have become 15 separate species of birds. This speciation is the result of different populations with varying traits becoming more specialized to feed on specific food items. There are now birds with large beaks who specialize in eating large, hard seeds, birds with smaller beaks that specialize in eating smaller seeds, and birds with sharp beaks who specialize in eating insects.