Proceedings of the fifth mountain lion workshop: 27

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62 PROCEEDINGS OF THE FIFTH MOUNTAIN LION WORKSHOP ASSESSING SUBSPECIES STATUS: A HOLISTIC EVALUATION OF THE YUMA MOUNTAIN LION Donald E. McIvor. Department of Fisheries and Wildlife, Utah State University, Logan, Utah 84322-5210 John A. Bissonette. Utah Cooperative Fish and Wildlife Research Unit, USGS Biological Resources Division, Department of Fisheries and Wildlife, Utah State University, Logan, Utah. 94322-5290. Key words: Arizona, California, Cougar, Puma concolor browni, Morphology, Mountain Lion, Subspecies Status, Taxonomy. Abstract Recent consideration of the Yuma mountain lion as a potential Threatened or Endangered species prompted us to examine the evidence supporting this population's designation as a subspecies. We took a holistic approach, examining taxonomic and ecological data and all published references to the subspecies. Currently available data casts the subspecific status into doubt. Existing data are inadequate for a rigorous morphometric comparison between this and surrounding populations, but we conclude C.H. Merriam's original basis for designating the Yuma mountain lion as a subspecies was incorrect. The Colorado Desert puma (Felis aztecus browni), was described on the basis of one specimen collected 19.3 km south of Yuma, Arizona (Merriam 1903). Subsequent taxonomic revision assigned this population to F. concolor browni (Young and Goldman 1946), and more recently to the genus Puma (Wilson and Reeder 1993). Merriam (1903) considered the animal to be smaller in skull morphology, particularly dentition, and paler and grayer in coat color than P. c. azteca, the adjacent subspecies occupying central and eastern Arizona. Merriam (1903) also believed the skull morphology of the specimen conferred adaptation to the desert environment, including a preference for smaller prey and a hunting strategy relying more on sight than hearing. Several published accounts building on Merriam's (1903) work delineated and expanded the range of F.c. browni. Grinnell (1914) conducted a biological survey on the Lower Colorado River (LCR) between 15 February-15 May, 1910. His range map for F.c. browni was based on sighting reports and 2 specimens donated to his party (Grinnell et al. 1937). Young and Goldman (1946) published the only major revision of F. concolor taxonomy, in which they expanded the range of F.c. browni beyond that suggested previously. Their evaluation also appears to be the first to have incorporated all 9 cataloged specimens. The most recently published range map indicated the widest range yet reported for F. c. browni (Duke et al. 1987). The reported range described a parabola extending south from Lake Meade, Nevada, expanding to encompass the LCR and the territory between Calexico, California, and Lukeville, Arizona. Recent literature on mountain lion ecology casts doubt on the taxonomic status of P. c. browni. Questions surround the ability of the extant prey base in P. c. browni's range to support an independent, self sustaining mountain lion population (Shaw 1989). Also, the documented ability of mountain lions to disperse and the apparent lack of barriers to also located specimens collected in the historic range of P. c. browni and gathered morphometric skull measurements dispersal suggests P.c. browni may be freely exchanging genetic material with adjacent mountain lion populations (Shaw 1993). Although no random population sample has been drawn from P. c. browni' range, evidence indicates few females (McIvor et al. 1994); hence reproduction in the area may be low or even non-existent (Peirce and Cashman 1993), lending support to the hypothesis that the region may be populated by mountain lions dispersing into marginal habitat from surrounding populations. Habitat degradation, particularly along the LCR corridor (Weaver 1982, Williams and Kilburn 1984, Shaw 1989, Hansen 1992), has likely reduced the region's ability to support a mountain lion population. Subsequently, the original indigenous population may have been driven to extinction, to be replaced by occasional mountain lions moving through the area from surrounding higher quality habitat. Recent publications have suggested an integrated approach involving natural history (including range and distribution), morphology, and molecular genetic data should be used to assess subspecific status (Ryder 1986, Avise 1989, O'Brien and Mayr 1991, Cronin 1993). We evaluated P. c. browni based on the suite of existing data, and suggest additional data needs to fully determine the status of this population. METHODS We evaluated the status of the Yuma mountain lion based on the current state of knowledge of desert-dwelling mountain lions. We examined >270 articles in the published literature and conducted interviews with >70 wildlife biologists and public land managers to determine whether available data support P. c. browni's subspecific status. We collected reports of mountain lion sightings, signs, and kills in the published range of P. c. browni as an indication of whether the area supports a mountain lion population. We (McIvor et al. 1994). We used the morphometric data to perform a canonical variate analysis (CVA) (Reyment et al.
PROCEEDINGS OF THE FIFTH MOUNTAIN LION WORKSHOP 63 1984) to address whether available morphometric data supported a taxonomic distinction for this population, and to assess the accuracy of Merriam's original claim that P. c. browni could be distinguished from conspecifics on the basis of tooth size. RESULTS AND DISCUSSION For clarity, we will consider the 3 lines of evidence (ecology, morphology, genetics) separately for the Yuma mountain lion, and then provide a conclusion synthesizing all 3 sources of information. Ecology We located 6 published range maps for this subspecies (McIvor et al. 1995); no consensus exists regarding the probable range of P. c. browni. Only the maps of Hall (1991) and Young and Goldman (1946) appeared to coincide, and Hall (1981) cited Young and Goldman (1946) as his source of information for P. concolor. We found that none of the authors satisfactorily explained the derivation of their maps, thus there was little basis for choosing one over another. We elected to use Duke et al.'s (1987) map because it encompasses the largest geographic area, and thus represents the most parsimonious approach to conserving biological diversity. Personal interviews and requests for information, as well as our review of the literature, produced 272 sighting reports of mountain lions within P. c. browni's published range. Of these reports 142 could not be confirmed, 17 were reports of specimens, and the remaining 113 reports were categorized as confirmed (McIvor et al. 1994). The densest grouping (43.8%) of sighting accounts occurred in the vicinity of Ajo and Organ Pipe National Monument (OPNM), Arizona. This clustering is an artifact of OPNM's systematic record keeping, the efforts of B. Broyles (pers. commun) to collect sighting accounts in the area of Cabeza Prieta National Wildlife Refuge, and the movement of mountain lions in the Ajo and Sauceda Ranges outside the eastern boundary of P. c. browni's range. The remaining accounts were scattered fairly uniformly across the range described by Duke et al. (1987). Interpretation of sighting reports and their implications is problematic (Van Dyke and Brocke 1987). Mountain lions appear to be seen with modest frequency throughout the study area, however, the frequency of sightings decreases as the core range (the area around Yuma) is approached. The distribution of sightings, particularly near OPNM, and the home range data collected by Peirce and Cashman (1993), indicate that the range boundaries delineated for P. c. browni have no biological relevance, and in many areas do not correspond to any isolating geographic barriers. Merriam (1903), based on his perception that the teeth of P. c. browni are smaller than those of conspecifics, hypothesized that the Yuma mountain lion subsisted on smaller prey than other subspecies. The larger body of literature documenting the importance of deer in the diet suggests that mountain lions in North America are dependant on some form of large prey for long-term population maintenance (Anderson 1983, Shaw et al. 1988). A study conducted on the eastern boundary of P. c. browni range also found deer to be the most frequently occurring prey item in mountain lion diets (Cashman et al. 1992). Finally, the food requirements of females with young (Ackerman 1982, Weaver 1982, Ackerman et al. 1986) suggests breeding populations of mountain lions may not be able to exist in the absence of large prey (Ackerman et al. 1984). Morphometry We located 17 specimens (10 M, 4 F, 3 unknown). Nine were officially cataloged in museums and 6 specimens were held in private collections (McIvor et al. 1994). Contact with museums revealed an additional animal collected from the Hualapai Mountains of Arizona, as well as a specimen collected on the Kofa National Wildlife Refuge in 1944 (Halloran 1946), that had not been cataloged as specimens of this subspecies. Partly because opinion varies between researchers regarding the important characters to measure, complete data for all skulls were not available from the literature (Table 1). Some skulls were incomplete, usually because of damage inflicted during collection, and dynamic terminology also contributed ambiguity to some measurements (e.g., "braincase height" and "greatest depth" were used interchangeably). Early analysis of mountain lion skulls and variation in pelage were based on subjective criteria. Powerful statistical tools are a relatively recent development unavailable to early taxonomists. CVA generates n-1 uncorrelated linear combinations of variables that maximize separation among a priori designated groupings (Bookstein et al. 1985). These variates, which are linear combinations of the original variables, provide a useful framework for displaying the magnitude of the interrelationship between the populations, and can be plotted and studied on a two dimensional graph (Reyment et al. 1984). Furthermore, each component (i.e., original variable) is assessed for its contribution to the separation between populations. CVA has the advantages of being easy to interpret, and only one statistical test is conducted, avoiding the ambiguities associated with a multiple test approach and protected alpha levels. However, CVA is highly sensitive to heterscedasticity, and to sparse data; a single missing variable results in the loss
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Proceedings of the fifth mountain lion workshop: 27

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