Archaeological Evidence of Anthropogenically Induced Twentieth-Century Diminution of North American Wapiti (Cervus Elaphus)
Lyman, R. Lee, The American Midland Naturalist
Translocated Rocky Mountain wapiti (Cervus elaphus nelsoni) released in the southern Cascade Range of Washington State in the early twentieth century hybridized with resident Roosevelt wapiti (C. e. roosevelti). Archaeological remains of wapiti from this area dating between 1400 A.D. and 1835 A.D. are significantly larger than both subspecies, but bones of descendant hybrid wapiti killed by the 18 May 1980 volcanic eruption of Mount St. Helens are intermediate in size between the two subspecies. Deer (Odocoileus sp.) remains from the same archaeological sites as the wapiti remains are no different in size than bones of modern deer, indicating size change in wapiti was not environmentally driven. Anthropogenically facilitated hybridization supplemented and likely saved the local population from extirpation but resulted in smaller individual animals.
During the early 20th Century Rocky Mountain wapiti (Cervus elaphus nelsont) were translocated from the Greater Yellowstone Ecosystem (GYE) of northwestern Wyoming to many areas in North America to supplement or re-establish what were perceived to be historically depleted or extirpated herds (Robbins et al., 1982; Wolfe et al., 2002). One of the areas to which wapiti were translocated was Washington State (Couch, 1935). Wapiti were released at various locations within the state, one of which is just east of what are now Mount Rainier National Park and Mount St. Helens National Monument (Fig. 1). It was known at the time that the western third of Washington was occupied by Roosevelt wapiti (C. e. roosevelti) (Murie, 1936; Skinner, 1936). This subspecies is larger in many dimensions than the conspecific Rocky Mountain wapiti (Bryant and Maser, 1982; O'Gara, 2002). The central third of the state comprises the Cascade Range. It was thought during the first half of the twentieth century that the Cascade Range previously had been occupied by Roosevelt wapiti that were largely, but perhaps not completely, extirpated by the end of the 19th Century (Taylor and Shaw, 1927; Murie, 1951; Bradley and Driver, 1981; Schullery, 1984). Efforts to supplement and reestablish these herds were made in the early 20th Century (Couch, 1935; Mitchell and Lauckhart, 1948). Rocky Mountain wapiti were known to occur in the eastern third of the state (Dalquest, 1948), and GYE wapiti also were released there early in the 20th Century (Couch, 1935). The archaeological record for the Holocene epoch (last 10,000 y) indicates that elk were widespread in the state (Dixon and Lyman, 1996; Harpole and Lyman, 1999), though as yet it is unknown where each subspecies occurred before the 19th Century (Lyman, 2004).
In 1968 it was reported that wapiti remains recovered from 10,000 y-old-sediments in Washington were larger than bones of modern wapiti (Fryxell et al., 1968). The size of the remains is not too surprising because remains of many genera and species of mammal dating to the late Pleistocene are larger than their modern counterparts (Guthrie, 1984). Wapiti remains recovered in the 1990s from archaeological sites in the northeastern portion of the Olympic Peninsula of Washington (Fig. 1) also are larger than modern wapiti (Lyman, 2004), but these remains are only about 1300-2500 y old. This suggested that rather than a chronocline of diminution throughout the Holocene as is evident for various other large mammalian taxa, Washington wapiti may have been large until quite recendy. Why did they become small so late in time?
If prehistoric native wapiti in Washington were large because of their genes, then they should remain large until their gene pool changed, after which smaller wapiti would be the norm. Two possible causes of gene pool change are: (i) hybridization with introduced nonresident wapiti and (ii) climatic change resulting in selection for smaller individuals. Signatures of the former cause include modern individuals with hybrid genotypes and no evidence of environmental change coincident with change in wapiti size. …