# The Lesson of the Kaibab KEY

Introduction: The environment may be altered by forces within the biotic community, as well as by relationships between organisms and the physical environment. The carrying capacity of an ecosystem is the maximum number of organisms that an area can support on a sustained basis. The density of a population may produce such profound changes in the environment that the environment becomes unsuitable for the survival of that species. For instance, overgrazing of land may make the land unable to support the grazing of animals that lived there.

Objectives:

• Graph data on the Kaibab deer population of Arizona from 1905 to 1939
• Determine factors responsible for the changing populations
• Determine the carrying capacity of the Kaibab Plateau

## Background

Before 1905, the deer on the Kaibab Plateau were estimated to number about 4000. The average carrying capacity of the range was then estimated to be about 30,000 deer. On November 28th, 1906, President Theodore Roosevelt created the Grand Canyon National Game Preserve to protect the "finest deer herd in America."

Unfortunately, by this time the Kaibab forest area had already been overgrazed by sheep, cattle, and horses. Most of the tall grasses had been eliminated. The firs step.......... (abbreviated, see original for full text)

## DATA

1. Graph the deer population data. Place time on the X axis and "number of deer" on the Y axis

Graph created at chartgo.com

 DATA TABLE Year Deer Population 1905 4,000 1910 9,000 1915 25,000 1920 65,000 1924 100,000 1925 60,000 1926 40,000 1927 37,000 1928 35,000 1929 30,000 1930 25,000 1931 20,000 1935 18,000 1939 10,000

## Analysis

1. During 1906 and 1907, what two methods did the Forest Service use to protect the Kaibab deer? hunting was banned and predators were killed

2. Were these methods successful? Use the data from your graph to support your answer. The deer population increased rapidly, which can be considered a success, at least at first

3. Why do you suppose the population of deer declined in 1925, although the elimination of predators occurred? overpopulated deer died to starvation or disease

4. Why do you think the deer population size in 1900 was 4,000 when it is estimated that the plateau has a carrying capacity of 30,000?

overgrazing of the area made the food supply smaller, not enough plants to feed population; competition with farm animals

5. Based on these lessons, suggest what YOU would have done in the following years to manage deer herds.

1915: reduced the number of grazing animals in the area to give more room to the deer populations, allowed hunting to reduce populations, possibly add more predators such as wolves to slow population growth and prevent mass starvation

1926: at this point the deer population were already declining rapidly, resources of the area may have been depleted due to overpopulation, you could add more deer or reduce hunting or predators to allow the deer to recover, but you wouldn't want to eliminate it entirely or the cycle would just start over again

6. It is a criticism of many population ecologists that the pattern of population increase and subsequent crash of the deer population would have occurred even if the bounty had not been placed on the predators. Do you agree or disagree with this statement. Explain your reasoning. Answers vary, predators do have a place in ecoysystems to keep prey species from becoming overpopulated.

7. What future management plans would you suggest for the Kaibab deer herd? Controlled hunting, possibly birth control for deer to keep their numbers smaller, introduce more predators