DID INTERSPECIFIC COMPETITION WITH THE GRAY WOLF (CANIS LUPUS) CAUSE THE EXTINCTION OF THE DIRE WOLF (CANIS DIRUS)?

The dire wolf (Canis dirus) was one of the most geographically widespread large carnivores living in the Americas during the late Pleistocene, occurring in at least 136 localities in North America, from Alberta, Canada southward, and at three sites in South America. Like many other large predators in the Americas, Canis dirus became extinct at the end of the Pleistocene. What caused the species' extinction? Ronald Nowak (1979) in North American Quaternary Canis hypothesized that competition between Canis lupus and Canis dirus may have contributed to the dire wolf's demise. Elaine Anderson (1984) in her mammalian bestiary chapter in the Quaternary Extinctions, A Prehistoric Revolution volume likewise proposed that competition with Canis lupus resulted in the dire wolf's extinction. This interspecific competition hypothesis potentially can be tested and rejected under three scenarios: 1) the dire wolf and gray wolf, in areas of sympatry, were ecologically dissimilar, 2) the dire wolf and gray wolf, if ecologically similar, were not sympatric, or, 3) the dire wolf and gray wolf were ecologically dissimilar and allopatric in distribution. Here the second, or geographic test, is evaluated. Canis lupus co-occurs with Canis dirus at 15 localities in North America and the two species likely were sympatric from southern Alberta, Canada in the north, southward across the lower forty-eight states in the United States, and into central Mexico. However, the gray wolf does not occur either historically or in the fossil record south of central Mexico, while the dire wolf extends into South America, occurring at Muaco (Venezuela), Talara (Peru) and Tarija (Bolivia). Even if the two canids were ecologically similar and competition occurred in areas of sympatry in North America, this does not explain the demise of Canis dirus in Central and South America. While the possibility remains that competition between Canis lupus and Canis dirus could have resulted in the extirpation of dire wolf populations in North America, competition with Canis lupus alone cannot have caused the dire wolf's extinction.