title: Nowhere to Go but Up: Impacts of Climate Change on Demographics of a Short-Range Endemic (Crotalus willardi obscurus) in the Sky-Islands of Southwestern North America.
abstract: Biodiversity elements with narrow niches and restricted distributions (i.e., 'short range endemics,' SREs) are particularly vulnerable to climate change. The New Mexico Ridge-nosed Rattlesnake (Crotalus willardi obscurus, CWO), an SRE listed under the U.S. Endangered Species Act within three sky islands of southwestern North America, is constrained at low elevation by drought and at high elevation by wildfire. We combined long-term recapture and molecular data with demographic and niche modeling to gauge its climate-driven status, distribution, and projected longevity. The largest population (Animas) is numerically constricted (N = 151), with few breeding adults (Nb = 24) and an elevated inbreeding coefficient (ΔF = 0.77; 100 years). Mean home range (0.07 km2) is significantly smaller compared to other North American rattlesnakes, and movements are within, not among sky islands. Demographic values, when gauged against those displayed by other endangered/Red-Listed reptiles [e.g., Loggerhead Sea Turtle (Caretta caretta)], are either comparable or markedly lower. Survival rate differs significantly between genders (female<male) and life history stages (juvenile<adult) while a steadily declining population trajectory (r = -0.20±0.03) underscores the shallow predicted-time-to-extinction (17.09±2.05 years). Core habitat is receding upwards in elevation and will shift 750 km NW under conservative climate estimates. While survival is significantly impacted by wildfire at upper elevations, the extinction vortex is driven by small population demographics, a situation comparable to that of the European Adder (Vipera berus), a conservation icon in southern Sweden. Genetic rescue, a management approach successfully employed in similar situations, is ill advised in this situation due to climate-driven habitat change in the sky islands. CWO is a rare organism in a unique environment, with a conserved niche and a predisposition towards extinction. It is a bellwether for the eventual climate-driven collapse of the Madrean pine-oak ecosystem, one of Earth's three recognized megadiversity centers.
authors.affiliation: Department of Biology, Colorado State University, Ft. Collins, Colorado, United States of America.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Davis
authors.affiliation: Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, United States of America.
authors.forename: Marlis R
authors.initials: MR
authors.lastname: Douglas
authors.affiliation: Department of Biology, Colorado State University, Ft. Collins, Colorado, United States of America.
authors.forename: Colleen T
authors.initials: CT
authors.lastname: Webb
authors.affiliation: Department of Biology, Western Kentucky University, Bowling Green, Kentucky, United States of America.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Collyer
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Holycross
authors.affiliation: New Mexico Department of Game and Fish, Santa Fe, New Mexico, United States of America.
authors.forename: Charles W
authors.initials: CW
authors.lastname: Painter
authors.affiliation: Department of Biology, University of Texas-El Paso, El Paso, Texas, United States of America.
authors.forename: Larry K
authors.initials: LK
authors.lastname: Kamees
authors.affiliation: Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, United States of America.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Douglas
mesh_terms: D000531:Altitude; D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D044822:Biodiversity; D057231:Climate Change; D017839:Crotalus / Q000235:genetics / Q000502:physiology*; D003710:Demography; D017753:Ecosystem; D005260:Female; D005390:Fires; D008297:Male; D009516:New Mexico; D009656:North America; D013534:Survival