Thermoregulatory behavior and high thermal preference buffer impact of climate change in a Namib Desert lizard 1,2, 3,4 3,5 6 3,7 SEBASTIAN KIRCHHOF, ROBYN S. HETEM, HILARY M. LEASE, DONALD B. MILES, DUNCAN MITCHELL, € 1,2 € 1,2 8 9 3,10 JOHANNES MULLER, MARK-OLIVER RODEL, BARRY SINERVO, THEO WASSENAAR, AND IAN W. MURRAY 1Museum fur€ Naturkunde, Leibniz-Institute for Evolution and Biodiversity Science, Invalidenstr. 43, 10115 Berlin, Germany 2Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Altensteinstr. 34, 14195 Berlin, Germany 3Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193 Johannesburg, Gauteng, South Africa 4School of Animal, Plant and Environmental Sciences, Faculty of Sciences, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, 2000 Johannesburg, Gauteng, South Africa 5School of Physiology, University of Arizona, Tucson, Arizona 85721 USA 6Department of Biological Sciences, Ohio University, Athens, Ohio 45701 USA 7School of Human Sciences, University of Western Australia, 35 Stirling Highway, Crawley, Perth, Western Australia 6009 Australia 8Department of Ecology and Evolutionary Biology, and Institute for the Study of the Ecological and Evolutionary Climate Impacts, University of California, 130 McAllister Way, Coastal Biology Building, Santa Cruz, California 95064 USA 9Gobabeb Research and Training Centre, P.O. Box 953, Walvis Bay, Namibia 10Pima County Office of Sustainability and Conservation, Tucson, Arizona 85701 USA Citation: Kirchhof, S., R. S. Hetem, H. M. Lease, D. B. Miles, D. Mitchell, J. Muller,€ M.-O. Rodel,€ B. Sinervo, T. Wassenaar, and I. W. Murray. 2017. Thermoregulatory behavior and high thermal preference buffer impact of climate change in a Namib Desert lizard. Ecosphere 8(12):e02033. 10.1002/ecs2.2033 Abstract. Knowledge of the thermal ecology of a species can improve model predictions for temperature- induced population collapse, which in light of climate change is increasingly important for species with limited distributions. Here, we use a multi-faceted approach to quantify and integrate the thermal ecology, properties of the thermal habitat, and past and present distribution of the diurnal, xeric-adapted, and active-foraging Namibian lizard Pedioplanis husabensis (Sauria: Lacertidae) to model its local extinction risk under future cli- mate change scenarios. We asked whether climatic conditions in various regions of its range are already so extreme that local extirpations of P. husabensis have already occurred, or whether this micro-endemic species is adapted to these extreme conditions and uses behavior to mitigate the environmental challenges. To address this, we collected thermoregulation and climate data at a micro-scale level and combined it with micro- and macroclimate data across the species’ range to model extinction risk. We found that P. husabensis inhabits a thermally harsh environment, but also has high thermal preference. In cooler parts of its range, individuals are capable of leaving thermally favorable conditions—based on the species’ thermal preference—unused during the day, probably to maintain low metabolic rates. Furthermore, during the summer, we observed that individ- uals regulate at body temperatures below the species’ high thermal preference to avoid body temperatures approaching the critical thermal maximum. We find that populations of this species are currently persisting even at the hottest localities within the species’ geographic distribution. We found no evidence of range shifts since the 1960s despite a documented increase in air temperatures. Nevertheless, P. husabe nsis only has a small safety margin between the upper limit of its thermal preference and the critical thermal maximum and might undergo range reductions in the near future under even the most moderate climate change scenarios. Key words: climate change; cost–benefit model; desert; ectotherm; Lacertidae; modeling; Namib Desert; reptile; thermoregulation. Received 4 October 2017; accepted 12 October 2017. Corresponding Editor: Debra P. C. Peters. Copyright: © 2017 Kirchhof et al. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. E-mail: [email protected] ❖ www.esajournals.org 1 December 2017 ❖ Volume 8(12) ❖ Article e02033 KIRCHHOF ET AL. INTRODUCTION thermal tolerances and to estimate the thermal quality of the current environment. These data Globally, some lizard populations may be at are then combined with climate change models risk of extinction due to a rapidly warming cli- to estimate restrictions in lizard activity in the mate, because ambient temperatures increasingly past (before observed temperature increases exceed the lizards’ thermal tolerances (Huey beginning in the mid-1970s), present, and future. et al. 2009, Sinervo et al. 2010). One possible Not all lizard species are at equal risk of extir- mechanism is reduction in time active outside pation from rising ambient temperatures. Several retreats, which translates ecologically into a con- factors may interact to influence a lizard species’ straint on available foraging time, particularly susceptibility to altered thermal niches arising threatening during the reproductive season from climate change, including the habitat when energy demands are at their peak. Abnor- requirements and characteristics, daily activity mally warm ambient temperatures have already patterns, and foraging behavior (e.g., Anderson been demonstrated to be associated with extinc- and Karasov 1981, Huey and Pianka 1981, Kear- tions of local lizard populations due to what has ney 2013, Tingley et al. 2013, Bohm€ et al. 2016). It been proposed to be an inability to balance the has been criticized that the model of Sinervo et al. energetic demands of reproduction in an abbre- (2010) did not explicitly include species-specific viated period of daily activity (Sinervo et al. habitat affinities, their microclimatic diversity, 2010, 2011). Despite the availability of strong cir- behavior (thermoregulation, foraging strategy), or cumstantial evidence, further examination of this life history (Kearney 2013). These factors are hypothesis is warranted. In addition, expanding potentially necessary to accurately assess climate- its application to a wider range of environments mediated lizard extinction risk, as has been found and lizard species is necessary. A combination of for the risk associated with viviparity in Mexican species-specific ecological data at a micro-scale, lizards (Sinervo et al. 2010). experimental approaches, and mechanistic spe- Deserts are among the most extreme habitats cies distribution modeling approaches is appro- that are occupied by lizards, due to the chal- priate for such hypothesis tests. lenges imposed by thermal and hydric con- Mechanistic species distribution models are straints. Namibia includes some of the warmest valuable tools for testing potential threats using and driest regions in Africa south of the Sahara real ecological data (e.g., Kearney and Porter Desert, yet these arid Namibian ecosystems sup- 2009, Sinervo et al. 2010, Kearney 2013). The Sin- port a high diversity of lizard species (Thuiller ervo et al. (2010) model is based on the hypothe- et al. 2006, Herrmann and Branch 2013). In the sis that species’ range edges were originally hyper-arid Namib Desert, which stretches nearly defined by the maximum operative temperatures 2000 km along the coast from southern Angola at the outermost localities of their distribution through Namibia to northern South Africa, sur- (i.e., hottest localities for the high temperature face temperatures often exceed 60°C (Edney physiological limit) before the onset of anthro- 1971, Lancaster et al. 1984, Seely et al. 1990, Viles pogenic climate change (considered as beginning 2005, Murray et al. 2014). Terrestrial lizard spe- during the mid-1970s following the Intergovern- cies that occur here are active in extreme environ- mental Panel on Climate Change [IPCC]; Bindoff mental conditions. Furthermore, the Namib et al. 2013). The Sinervo et al. (2010) model Desert is home to a rich array of endemic lizard integrates lizard thermophysiology and in situ species that have specific habitat requirements operative temperatures (Te) to elucidate the inter- and may be particularly vulnerable to changes in relationships between ambient temperature and their environment (Sinervo et al. 2010). population distribution. This model relies on the Regarding foraging strategies, lizard species premise that ambient temperatures constrain the may be broadly characterized by using either an amount of time that lizards may be active out- active or a sit-and-wait (or ambush) foraging side of their retreats (during which time lizards mode (Pianka 1966). Daily foraging time and for- complete life activities such as foraging and aging strategy are strongly correlated. For exam- breeding). In this model, site- and taxon-specific ple, sit-and-wait foragers usually have lower empirical data are used to determine species’ prey encounter rates and are therefore surface ❖ www.esajournals.org 2 December 2017 ❖ Volume 8(12) ❖ Article e02033 KIRCHHOF ET AL. active for longer periods of time than actively snout-to-vent length of 45–61 mm and a mass of foraging lizard species, and have lower field 1.8–4.2 g (Branch 1998). The species occurs in