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Kaibab deer from the DOCUMERICA series, a program sponsored by the Environmental Protection Agency to photograph subjects of American environmental concern during the 1970s, May 1972 image
At the beginning of the 20th century, the Kaibab Plateau was witness to an interesting experiment in what some might call population engineering. The plateau's pre-1905 population of mule deer was estimated to be around 4,000. This number was never confirmed by any kind of count or survey, and has become an accepted number mainly because no other estimate is available. The average carrying capacity of the land was unknown, in part because this concept was not widely used by naturalists at the time. Years later, Aldo Leopold estimated that the capacity had been about 30,000 deer.[citation needed]
The idea in 1906 was simply to protect and expand the herd, so on November 28, President Theodore Roosevelt created the Grand Canyon National Game Preserve. Overgrazing by herds of sheep, cattle, and horses had taken place on the plateau since the 1880s. During that time, many predators were also killed by ranchers and bounty hunters. By the time Roosevelt established the game preserve, ranchers had moved most domestic livestock elsewhere. The primary change brought by the creation of the game preserve was to ban deer hunting. Government efforts, led by the United States Forest Service, began to protect the deer's numbers by killing off their natural predators once again; to this end, between 1907 and 1939, 816 mountain lions, 20 wolves, 7388 coyotes and over 500 bobcats were reportedly killed.
The deer population experienced a great increase in numbers during the early decades of the 20th century. One estimate put the population as high as 100,000 deer inhabiting the range in 1924. Again, there was no systematic survey to support this estimate, which may have been exaggerated to twice the actual number. Shortly after that time, however, the deer population did begin to decline from over-browsing. By the mid-1920s, many deer were starving to death.
After a heated legal dispute between the federal government and the state of Arizona, hunting was once more permitted, to reduce the deer's numbers. Hunters were able to kill only a small fraction of the starving deer. The range itself was damaged, and its carrying capacity was greatly reduced.
Prey and predator population dynamics[edit]
X Fire Tree Planting Restoration Project, Kaibab National Forest,April 2012
Once ecologists began to study the area and reflect on the changes that had occurred there, they began to use the Kaibab deer as a simple lesson about how the removal of the deer's natural predators, which had been done in the interest of preserving the deer population, had allowed the deer to over-reproduce, and quickly overwhelm the plateau's resources. Some ecologists suggested that the situation highlighted the importance of keeping a population in balance with its environment's carrying capacity.
The more meaningful lesson of the Kaibab suggests that human efforts to protect wildlife and preserve wild areas must be balanced with ecological complexity and social priorities that are difficult to predict. Changes take place, sometimes rapidly, but their effects linger for decades. Today, the Arizona Game Commission manages the area, controlling the numbers of deer as well as predators, and issues hunting permits to keep the deer in balance with the range.
Kaibab Lake in the Williams Ranger District, Kaibab National Forest, August 2020
Although the story of the Kaibab deer rose to fame in the 1920s due to their sudden increase and decrease in population, the story can also be used to demonstrate the way in which scientific studies and ideas about history can help educate current students. The first interpretation of the deer story as demonstrated in textbooks was that predator control had destroyed the deer's population growth. It was thought that initially the high number of deer predators were obtruding the growth of the deer's population, therefore rules were put in place in order to minimize the predator population and allow the deer to increase their population size. However, as scientific studies continued, ecologist Graeme Caughley suggested that predator control alone could not have caused the Kaibab irruption, but rather factors like climate, grazing by other animals, and preservation policies actually had more significant impacts on the deer
Caughley's opinion led to confusion by teachers and scientists over what to include and teach in ecology and biology classes, therefore this story stopped being used as an example of prey and predator population dynamics. This is important to the development of scientific studies because it shows that events—like the Kaibab deer controversy—do not have a definitive start and beginning but include other opinions and approaches which teachers use to showcase the richness of controversy.
In the summers of 2002 and 2003, forest ecologist Dan Binkley and associates undertook a careful analysis of the age structure of aspen stands on the Kaibab. Their work shows that few aspen sprouted successfully on the plateau in the 1920s. They ruled out browsing by domestic livestock or exceptionally dry conditions as causes of that change and concluded that the age structure of aspen in the area was probably due to a period of severe overbrowsing by a large population of deer. This, they write, is consistent with the original assessment of the rapid rise in deer population as a result of persistent predator control. Their contribution of original research is a refreshing addition to the ongoing discussion of predator-prey interactions on the Kaibab. [Binkley, Dan, et al., 2006. "Was Aldo Leopold right about the Kaibab deer herd?" Ecosystems 9: 227–241]
The Kaibab deer controversy has revolutionized the way science is taught in textbooks, and the way students question ecology and biology. In addition, students now learn that human intervention can lead to big repercussions regarding specific animal's population and development in certain regions.[citation needed]
