Predation, Competition, and Pleistocene Megafauna Extinction

Abstract

In recent years people have hypothesized that the major Pleistocene extinction of large mammals may have been brought about by man (Martin and Wright, 1967; Reed, 1970). Man's agency in megafauna extinction has strong arguments both pro and con. Recently, a more sophisticated explanation based on ecological interaction between man, carnivores, and large herbivores has been offered by Krantz (1970), suggesting man could have been indirectly responsible for the extinction of some species. Basically Krantz' hypothesis is that while carnivores tend to specialize on extremely young and extremely old prey, man, especially culturally more developed man, spreads his kill more evenly across all age classes (Fig. 1). That is to say, most carnivores prey upon the the most accessible prey, the bulk of which are the very old and the very young. This results in the stepwise survivorship curve of Figure 1. Man, on the other hand, once he had developed projectile weapons and other sophistications in hunting which permitted him to prey at a distance, could remove, almost equally well, animals of all age classes. This results in a survivorship curve such as the smooth curve in Figure 1. When primitive man migrated into an area, he was a superior competitor to the large carnivores which eventually became extinct. Man as the new predator changed the survivorship curve of his favored herbivore prey which resulted in a twostep modification of the overall herbivore population: (1) With man taking proportionally fewer of the young, the prey species expands in numbers and presumably territory. The prey species expands because Under human predation these individuals [surviving young adults], the major breeding stock, are far more numerous because their numbers were not so drastically depleted when they were still immature. (2) Other herbivores are exterminated by pressure from the favored prey through competition for such things as food under stress conditions. This, in turn, would result in the extinction of additional carnivore species through loss of their prey. Using the example of Pleistocene North America, Krantz believes that the saber-toothed cats became extinct be-