Chapter 16. The Kaibab Deer Herd

This chapter illustrates the iterative nature of the modeling process with a concrete and important example. The example is the deer population that occupied the Kaibab Plateau at the turn of the century. The Kaibab deer herd warrants special attention because of its sudden and explosive growth in the early years of the century.

A sudden increase in an animal population is called an irruption. The Kaibab irruption is thought to be the first of a series of irruptions "which have since threatened the future productivity of deer ranges from Oregon to North Carolina, California to Pennsylvania, Texas to Michigan." Leopold (1943) reports having found no record of a deer irruption in North America "antiquating the removal of deer predators. Those parts of the continent which still retain the native predators have reported no irruptions." Leopold interprets this as circumstantial evidence to support "the surmise that removal of predators predisposes a deer herd to irruptive behavior" (Leopold 1943). The Kaibab story has become widely known as scientists interpret and reinterpret the cause and consequences of the irruption (Botkin 1990, Caughly 1970, Kormondy 1969, Lack 1954, and Odum 1971).

This chapter uses the Kaibab example to provide an opportunity for model building and testing. The main purpose is to illustrate the iterative, trial and error process explained in the previous chapter. This is a long chapter which does not reach its destination immediately. Along the way, you will appreciate the many decisions to be made in building a model. By the end of the chapter, you will see a model which simulates the dynamics of the deer herd irruption and the subsequent collapse due to starvation. The chapter concludes with exercises to verify, apply and improve the model. One of the more challenging exercises is to expand the model to learn if it can accommodate alternative interpretations of the Kaibab irruption.