The carrying capacity of an ecological system refers to the total number of a species in a particular area, which is supported conveniently without degradation. Arizona’s Kaibab Plateau had a carrying capacity of 30,000 animals as at 1905 (Allen, 2013). The United States Forest Reservists considered the need to protect deer on a 300,000-hectare range of the plateau as the studies at the time revealed that the population significantly declined to slightly below 5,000 deer. The causative factors established included competition from other grazers such as cattle and sheep, but substantially the predator population. The animals that were predating on the deer comprised of coyotes, wolves, mountain lions, bears, and bobcats. Thus, this report seeks to describe the relationship of the deer herd in Kaibab Plateau to the carrying capacity, the effects on the crowd of various actions taken by the Forest Service from 1907-1920, and the lessons learned by the U.S. Forest Service as from 1905 to 1939.
The Relationship of the Deer Herd to the Carrying Capacity
Kaibab Plateau has a carrying capacity of 30,000 deer at any one point in time (Allen, 2013). Thus, the most suited population that would not degrade the environment, but still inhabit the place comfortably would be close to, but not more than the carrying capacity (Allen, 2013). Appendix 1 highlights the deer population over time; various deductions are made on the relationship of the deer herd to the carrying capacity. Over the years from 1905, the carrying capacity was optimal for close to a decade; then the population hiked to over 60, 000 deer by 1920. The rise in numbers of this species attributes to the probable reduction in competition for grazing lands, reduction in predators, as well as the creation of refuge and protected nature of the deer by policy measures. As at 1924, the carrying capacity was overwhelmingly overstretched, and most likely, feeding resources must have become scarce for the population. Evidently, from Appendix 1, the community tripled the Kaibab Plateau’s carrying capacity. Thus, the above information confirms the probable conducive environment that led to the population explosion. However, the populace sharply decreased after 1924 from approximately a hundred thousand deer to sixty thousand and then to forty thousand by 1926, which is a substantive decline. Towards 1930, there is a plateau, meaning the population was reasonably optimal relative to the carrying capacity and after that, it grew negatively to the optimal, standing at around ten thousand as at 1939 ((Allen, 2013). The trend observed in the graph highlights a steady population growth that surpasses the optimal greatly, forcing natural factors such as lack of grass to graze or diseases to control the population to optimal and then below optimal (Eisenberg, 2013). The above is proof that nature is self-evaluating.
Effects of Various Actions Taken by the Forest Service from 1907-1920
An excessive decline in the deer population in 1905 attracted attention from various quarters, including policymakers and most significantly, Theodore Roosevelt, who then proclaimed the Kaibab plateau as a refuge from 1906. The proclamation meant that different protective actions were undertaken inconsequential years, from1907 to 1920, and the same had substantial effects to the deer population and the environment at large due to disruption of the delicate balance of nature. The main competitors of the deer were dispersed from that land, including horses, cattle, and sheep, as well the elimination of deer predators such as coyotes, wolves, mountain lions, and bobcats. As a result, the grazing land incurred excessive growth of grasses and shrubs upon which deer fed on. The abundance of food meant that the population would quickly reproduce. However, lack of predators meant that there was no population control for the deer. Hence, the populace grew ten-fold to over 60,000 deer in 1920 and over 100,000 in 1924.
Excessive population growth thus reached an uncontrollable maximum; food thence grew scarce due to internal competition. Other aspects such as diseases greatly wiped out the population after 1924 (Millstein, 2014). The occurrence of a sudden drop in the deer population in an environment with no competitors and predators depicts the classic instance of the impact of interfering with the predator-prey relationship. Also, there is the proof of deferred density-dependent death, which refers to the observation that a population if left unchecked by laws of nature such as competition and predators, ends up killing itself due to internal competition for resources, as well as emerging issues such as diseases.
Lessons Learnt from 1905-1939
A vital aspect to note is that forest reservists and policymakers alike learned that it is essential to incorporate ecological complexities in decision making over what is observed as an ‘unwanted’ trend in nature (Forrester, 2014). The understanding of dependencies and relationships between species enables the consideration of the ripple effects of altering any of the populations in the ecosystem. For instance, the decision to eliminate predators from Kaibab plateaus was right to enable the deer population to grow, but was not prudent on other implications.
Also, the Kaibab Plateau deer population occurrence from 1905 to 1939 teaches much about letting nature balance itself out. The aforementioned is evident in the fact that, had the policymakers left to nature to redefine itself, the decrease in deer population certainly would give way to reduced predator population, an increase in viable grazing fields and rise in deer population once again (Millstein, 2014). The take away from such events enables students, researchers and ecology professionals to cautiously initiate changes in nature to achieve its delicate balance.
The Kaibab Plateau had a decline in deer population due to increased competition for grazing fields by cattle and a rise in the number of predators feeding on the deer. Thus, it was logical, but not prudent in the long run, to eliminate competitors and predators to the deer. As such, the population of this species rose rapidly and depleted available resources such as grass and water, eventually experiencing challenges such as diseases and death due to lack of sufficient food. Over the years of observation of the phenomena on the plateau, critical lessons about letting nature balance itself have been learned. Therefore, it is wise to consider the long term effects of any slight alterations in the ecosystem.
Allen, G. E. (2013). “Culling the Herd”: Eugenics and the Conservation Movement in the United States, 1900–1940. Journal of the History of Biology, 46 (1), 31-72.
Eisenberg, C. (2013). The wolf's tooth: keystone predators, trophic cascades, and biodiversity. Washington: Island Press
Forrester, T. D. (2014). Effects of predation and forage availability on the survival of black-tailed deer (Odocoileus hemionus columbianus) in the Mendocino National Forest, California. California: University of California, Davis.
Millstein, R. L. (2014). Types of Experiments and Causal Process Tracing: What Happened on the Kaibab Plateau in the 1920s? California: University of California, Davis Appendices
Appendix 1: Graphical representation of the Deer Population on Kaibab Plateau
Abbildung in dieser Leseprobe nicht enthalten