A Historical Resurvey of Flatland Lizards in the Mojave Desert
Historical resurveys are uniquely valuable for the information that they provide regarding population responses to environmental changes. As anthropogenic impacts on the environment proceed, such efforts are becoming increasingly important for developing a historical baseline and for understanding how contemporary populations respond. We undertook a >50-year historical resurvey of the Mojave Desert flatland lizard community by pairing data from the 1960s and today, which provided a repeatable benchmark for future monitoring. We found few changes in distribution, with at least 9 of 11 species continuing to occur where they were previously detected. However, we found marked declines in abundance for the widespread and highly detectable Side-blotched Lizard (Uta stansburiana), one of three species where data were sufficient to robustly estimate abundance. Both our work and other recent works highlight the difficulty of estimating abundance for wild lizard populations and, should we wish to understand declines before they turn into extirpations, call for the continued development of methods for efficient and robust tracking of desert reptile populations.ABSTRACT
Observed climate changes in the Mojave Desert.
Top panels (A-B) show differences in (A) Annual Precipitation and (B) Mean Annual Temperature between mean current conditions (2015-2017, 2022) and mean 1960s conditions (i.e., “past”, 1963-1964). Positive values indicate increases over time (i.e., wetter or hotter); negative values indicate decreases over time (i.e., drier or cooler). Circles are study sites; clockwise from northernmost site and labeled in (A): Grapevine (V), Pahrump (P), Kingston West (KW), Kingston East (KE), Searchlight (S), Twentynine Palms (T), Pisgah Crater (PC), Mojave (M). Axes are latitude and longitude, and thin borders are state boundaries. Bottom panels (C-D) show annual values from the 1960s and current time periods in color for each site, with the mean ± SD in black and white. Means were calculated by averaging across years within sites for the 1960s and current time periods, then averaging across sites within time periods.
Side-blotched Lizard (Uta stansburiana; A, C) and Whiptail (Aspidoscelis tigris; B, D) abundance over time.
Panels A and B: 1963-1964 data are replotted from Figure 11 and Table 18 in Pianka (1965), and 2015-2022 data are from distance model estimates (± SE). Panels C and D: Model-estimated mean values (± SE) during 1960s (i.e., “past”, 1963-1964) and current (2015-2022) time periods. Colors and letter codes are sites: V = Grapevine, M = Mojave, P = Pahrump, S = Searchlight, T = Twentynine Palms. Note that the y-axis scale varies across panels. Past data were unavailable for Side-blotched Lizards at the Pahrump site.
Density estimates over time for current sampling from distance models for all study sites.
Units for density on the y-axis are lizards per hectare, and error bars are SE. Note that the y-axis scale varies across panels. Colors and letter codes are sites: V = Grapevine, M = Mojave, P = Pahrump, S = Searchlight, T = Twentynine Palms, KE = Kingston East, KW = Kingston West, PC = Pisgah Crater.
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