The student will:
- Examine a conceptual linear model depicting how elk respond and survive in a non-thermally influenced area.
- Compare and contrast a conceptual linear model depicting how elk respond and survive in a hydrothermally influenced area.
The upper Madison River of Yellowstone National Park drains a volcanic caldera and contains thousands of hydrothermal features. Ungulates wintering in the upper Madison River area tend to congregate in thermally influenced sites for long periods during the year because hydrothermal heat reduces the snow level and provides refuges of food and warmth.
In contrast to non-thermally influenced stream drainages, research has shown that the soils, stream sediments, and water of the upper Madison River contain significantly higher levels of both fluoride and silica. These geochemical differences are further reflected in much of the vegetation that grows in this area. Ungulates in the Upper Madison River drainage consume a considerably higher dietary intake of both fluoride and silica than their counterparts in non-thermally influenced sites.
Conclusions: Research has indicated that high levels of fluoride results in ungulate tooth decay, which is accelerated by the scraping action of the silica. The severe tooth decay makes it difficult for the affected ungulates to consume healthy diets, resulting in an early onset of aging. Elk in the Madison River drainage have considerably shorter life spans than their counterparts in non-thermally influenced areas.
The instructor will:
- Tell students that elk wintering in the central part of Yellowstone tend to gather around the geyser basins and hot springs. Ask the students for their opinions as to why this happens. (Answer: Hydrothermal features provide refuges of warmth. Also, hydrothermal activity heats the ground temperature, which affects the snow pack and changes the area’s climate. This enables plants to grow in larger quantities for longer periods of time, which provides plentiful food for elk and bison.)
- Give each student a copy of Attachment A—Linear Model Worksheet (pdf)
- Explain that the first Linear Model on Attachment A illustrates a simple model depicting normal elk survival in a non-thermally influenced area of Yellowstone.
- Lead a discussion, following this Linear Model from top to bottom. Begin with the basic ecological drivers of “Sunlight, Soil, Water, and Temperature,” and ask what effect each has on plant growth in an area. Continue down the model, eliciting student response at each level.
- Proceed to the following page on Attachment A, and ask students to consider what happens when a hydrothermal influence is added. They should respond in writing to the changes they would expect at each level of the model. (Answer: Hydrothermal influence changes the soil, water, and ground temperature of an area by creating warmer conditions. This added warmth means less snow. Plants are able to grow in abundance and for longer periods of time. More forage means that more elk congregate on such sites and have ample food. Plentiful forageshould mean that the elk are healthier and live longer.)
- Ask students why the elk in hydrothermal areas live between 5 to 10 years less than their counterparts in non-thermal areas, where forage is often limited? Provide a clue: In addition to experiencing increased temperatures, the soil and water in hydrothermal sites also undergo chemical changes—water, soil, and vegetation of hydrothermal areas contain significantly higher levels of silica and fluoride. Silica is hard and abrasive, and excessive fluoride causes tooth decay.
- Direct the students to respond to Linear Model B in writing, showing more completely how hydrothermal influences may affect wildlife health and survival. (Answer: Hydrothermal influence changes the chemistry and temperature of soil and water. Increased temperatures means that less snow will accumulate, enabling plants to grow more abundantly and for longer periods of time. More forage means that more elk congregate on such sites. The more food the elk consumes in a hydrothermal area, the higher its dietary intake of fluoride. Excessive fluoride leads to tooth decay which is worsened by the scraping action of the silica. Severe tooth decay affects the animal’s ability to eat. When the animal’s health declines, it becomes an easy mark for predation, starvation, or disease.
National Science Standards for Grades 5-8