Prairie Adaptations

Lesson Introduction

Tallgrass prairies are ecosystems which have been formed by a particular combination of abiotic conditions, post-glacial topography, precipitation, evaporation, sunlight and temperature. They are maintained by the perpetuation of these conditions combined with the effects of periodic wild fires, droughts, and grazing animals. See The Tallgrass Prairie in Illinois.

The plants associated with a tallgrass prairie are those which have evolved features suited to this combination of elements. Deep roots, for instance allow plants to tap ground water in times of drought. Rhizomes allow plants to survive the periodic fires, which prevent trees from taking over. As the season progresses and the grasses grow taller, different forbs come into flower at heights parallel to the height of the grass. These and others are examples of plants' adaptations to the conditions that form and maintain a tallgrass prairie. See The Tallgrass Prairie in Illinois. In this lesson, students are asked to consider changes in prairie conditions and the survival of prairie plants.

Read about the mechanisms that drive evolutionary change in Introduction to Evolutionary Biology and Observed Instances of Speciation.

Illinois State Goal	Standard	Learning Benchmarks
12	B	5b. Compare and predict how life forms can adapt to changes in the environment by applying concepts of change and constancy.

Lesson Objectives

The students will:

• examine how some tallgrass prairie species are adapted to the conditions of their ecosystem.
• predict in writing and drawing how a species might change its form or behavior to adapt to new conditions (e.g., temperature, precipitation, atmospheric composition, or disappearance of an interdependent species).

Time Allotment

From one 40 minute period to an ongoing research project

Materials

• Index cards
• Pencils, markers, etc.
• Access to Internet resources and/or library for background and research

Teacher's Note

PROCEDURE

Tap Prior Knowledge

1. Discuss the following questions with the students: How can organisms change? What causes organisms to change? Evolution occurs in several ways: Natural selection, whereby the organisms least able to survive will not live to pass their genes to the next generation. It can also occur during genetic drift, where the tendency to mutate slowly causes isolated populations to speciate. Punctuated equilibrium may also alter an organism. This phenomenon of rapid change in an organism's physiology due to the more frequent occurrence of extreme mutations, which may be caused by a chemical trigger sensitive to environmental changes.

Share with Neighbor

2.Have the students work in pairs to describe how prairie plants are adapted to their particular conditions. Have the pairs of students create a flash card that describes this adaptation.

Hands-on Activity

3. Through writings and drawings, show several of these scenarios and the subsequent mutations in the plants over ten successive generations that might help the species survive the new conditions:

• precipitation decreases
• increased ultraviolet radiation
• chemical pollution in the air, water, and soil increases to toxic levels
• competition from alien species increases
• new predatory insects appear

Introduce Scientific Principle/Environmental Issue

4. Organisms which are do not evolve to adapt to their environment become extinct. A species is considered extinct when there are no more individuals of that species. The debate about human origins contains such a scenario, there are arguments that modern humans as a species evolved from a species known as homo erectus, but others suggest that h. erectus was a "dead end", meaning its individuals did not adapt and survive, and we, homo sapiens, evolved from a different line.

You might think there are no more dinosaurs, and technically, that is correct. However, there is evidence that modern birds are the evolved form of one species of dinosaur that was able to mutate and survive the changing conditions of the environment.

The cause of extinction for many species also does not allow them to mutate and survive. These processes take time to pass on to generations. Extinction is often the result of environmental changes that happen too fast for evolution to save a species. In the tallgrass prairie, some animal species, such as bison, need lots of space. There is now very little area of tallgrass prairie left, certainly not enough for bison. Biologists have realized that there are many species which only exist in certain, small ecosystems, such as islands. When these areas are destroyed, those species have no time to adapt to conditions, especially when there are alien species to compete with. The tallgrass prairie is no different. There are a few species which depend entirely on this habitat, and are found only in a few places. If these places become destroyed by development or pollution, those species will go with them, another "dead end" of evolution.

In some of this lesson, the reality of the scenarios may be different than the evolutionary model. Consider the decrease in precipitation, the existing community of plants may not evolve, but instead be replaced by plants which are already suited to the new conditions. This process is recorded in tallgrass prairies, where an increased rainfall and decrease in wildfires allow trees and forest plants to grow where there previously were prairie plants. The forest species out-compete the grasses when conditions favor them. Conversely when rainfall decreases, trees give way to grass and as rain continues to decrease as it does going west across the grassland, tallgrass species give way to shortgrass species, which them give way to desert plants.

This lesson shows how a species, given its ability to compete with better-adapted species, can mutate into a form that can compete on equal terms. A good example of this is the resistance to chemical pesticides insects can pass on to succeeding generations. Many of the insects may have been killed by the pesticide, so the ones which survive pass on whatever genetic traits helped them resist the poisonous effects. Similarly, the few individual prairie plants which happen to be shorter than normal may survive a decrease in precipitation and pass on that characteristic to their offspring. The ones with an unusually high level of distasteful alkaloid in them may not be eaten by an invading alien insect. Those plants with a purplish color may reflect UV rays.

Learning Outcomes

Students will:

• predict how a species may evolve to adapt to new environmental conditions.

Internet Resources

The Talk Origins Archive: Evolution FAQs
Introduction to Evolutionary Biology
Links to Evolution, Behavior, Ecology, Biology Education, Dinosaurs, etc.
Evolution Models
Observed Instances of Speciation
Kenneth R. Robertson