The following is a paper written and contributed by Dr. Erika M. Nowak of the Colorado Plateau Research Station and Biological Sciences at Northern Arizona University, Dr. Gordon W. Schuett of the Department of Biology and Center for Behavioral Neuroscience at Georgia State University, and Dr. Rulon W. Clark of the Department of Biology at San Diego State University.
Climate change is predicted to profoundly affect the distribution and viability of numerous plants and animals, and species restricted to specialized habitats are particularly vulnerable. Thus, pitvipers that are currently not protected actually may be at acute risk of extinction in the near future. Recent analyses of the projected impacts of climate change on the Arizona Black Rattlesnake (Crotalus cerberus) serve as an important case study. Arizona Black Rattlesnakes are endemic to Arizona and extreme western New Mexico (USA), occurring at elevations between 900 and 3000 meters (Degenhardt et al. 2005, Brennan and Holycross 2006). They are largely restricted to woodlands and shrublands in north and central Arizona and New Mexico, and to mountain ranges and riparian drainages in southeastern Arizona. The species is currently viewed as locally common or abundant, listed as “Secure” (Rank = G5) by NatureServe, and has yet to be assessed for the IUCN Red List. Furthermore, it is not given any special management protection by state or federal management agencies. Arizona Black Rattlesnakes are strongly associated with springs and riparian habitats, and they use downed woody debris for ambush cover (Schofer 2007, Nowak and Schuett 2014). In high elevation areas, they are mostly dependent on communal hibernacula and rookeries in substantial rocky outcrops; in lower-elevation areas they appear to seek out rocky drainages as refugia. Recently, graduate students have noted in their masters’ theses (Schofer 2007, Amarello 2012) the complexity of social interactions and parental care in C. cerberus. The Arizona Black Rattlesnake is unique among Arizona species in that it exhibits ontogenetic as well as physiological color change, in which adult individuals can assume at least three separate color phases.
Two research teams have independently identified Arizona Black Rattlesnakes as a species of particular management concern, due to predictions for substantial range contraction as a result of climate change (van Riper et al. 2014, Douglas et al. 2014). Future increases in temperature and concurrent decreases in rainfall and stream surface flow predicted for the southwestern U.S. are expected to result in substantial loss of Ponderosa Pine and Pinyon-Juniper Woodland habitat, due to direct mortality, spread of forest pests and catastrophic wildfires (Barnett et al. 2008; Williams et al. 2012). Given current distribution patterns for this species, these changes are expected to disproportionately impact habitat suitability for low-elevation populations of C. Cerberus. By explicitly modeling current and future ranges using landscape and biotic (plant) niche variables and climatic global circulation models, van Riper et al. (2014) forecast a 32% to 46% decrease by 2099 in the range currently occupied by C. cerberus. The range of variation was predicated on differing assumptions about the species’ dispersal abilities–loss was most extensive for low-elevation populations. Douglas et al. (2014) used genetic diversity analyses and North American bioclimatic variables to derive an environmental niche model encompassing yearly trends, seasonality and extreme environmental conditions. They also predicted range contraction due to changing climate and habitat loss as a result of wildfire, exacerbated by the species’ relatively shallow genetic divergence.
Both teams presented their research at the Biology of the Pitvipers 2 conference in Tulsa, Oklahoma, June 4-7, 2014 at the Double Tree Hilton.
Given modelling predictions for widespread range contraction, funding for long-term monitoring and determining the importance of actors driving its current distribution (especially in western New Mexico) would seem to be warranted. As well, additional research on the ecology, physiology and sociality of Arizona Black Rattlesnakes in the wild could elucidate possible management strategies for helping this species acclimate to climate-change induced stressors such as protracted drought coupled with extreme high temperatures.
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van Riper, C., III., J.R. Hatten, J.T. Giermakowski, D. Mattson, J.A. Holmes, M.J. Johnson, E.M. Nowak, K. Ironside, M. Peters, P. Heinrich, K.L. Cole, C. Truettner, and C.R. Schwalbe. 2014, Projecting climate effects on birds and reptiles of the Southwestern United States: U.S. Geological Survey Open-File Report 2014‒1050, 100 p., http://dx.doi.org/10.3133/ofr20141050.