Global biodiversity is declining as a direct result of anthropogenic climate change. Ectothermic species have become focal organisms for studying the ecological effects of altered climates due to the clear relationship between environmental temperatures and ectotherms’ basic physiological functions. Historically, examinations of these effects have focused heavily on heliothermic lizards, and most others have tended to focus on single populations or sympatric species within a single community. Addressing the longterm energetic implications of environmental temperature variation will provide valuable insight into the cascading physiological effects that certain populations or species may experience as a result of altered climates. In this study, we used thermal and behavioral data collected between 2010 and 2017 from four distinct populations of Pacific rattlesnakes (Crotalus oreganus) on the Central Coast of California. Two of these populations occupy thermally mild, coastal habitats while the other two occupy more thermally dynamic, inland habitats. Using operative temperature models, surgically implanted temperature loggers, and radiotelemetry, we collected data on the thermal microhabitats available within each of these study sites as well as field active body temperatures for 85 individual snakes. With the addition of a lab-derived preferred body temperature range, we determined the thermal quality of each site and the thermoregulatory accuracy of snakes from each population. Field behavioral observations, gathered from snakes at all four sites simultaneously during the year 2017, revealed how snakes utilize the thermal landscape and adjust thermoregulatory behavior to mitigate the effects of different climates. Although overall thermal quality was best at coastal sites, thermal quality of the microhabitats within each site varied greatly. Consistent with findings in other squamate reptiles, inland snakes thermoregulated more accurately, despite being in more thermally constrained environments. Despite the fact that coastal snakes had lower mean field active body temperatures, the preferred body temperatures of snakes were the same across all four sites. However, field active body temperatures were consistently lower than the preferred range, suggesting there are additional variables that influence thermoregulatory behavior. Using established equations estimating the resting metabolic rates of snakes based on body mass and temperature, we calculated resting metabolic rate and annual baseline maintenance energy expenditure for each population. Coastal snakes, which had lower field active body temperatures, had overall lower metabolic rates than inland snakes, but upon correcting for mass, snakes at neither coastal nor inland sites differed in metabolic rates. Therefore, the majority of the differences observed in metabolic rates are driven by body size and not field-active body temperature. Inland snakes need, on average, approximately 1.6x more food annually than coastal snakes. Due to overall low resting metabolic rates, this translates to snakes at all sites needing less than one ground squirrel (their most common food item on the Central Coast) per year to fuel basic physiological functions. Finally, we used conservative predictive climate change models allowing either 1°C or 2°C increases to predict changes in the thermal quality of each site and ensuing changes in snake metabolic rates and maintenance energy expenditure. Due to the relatively high preferred body temperature of C. oreganus, thermal quality of the environment will actually increase under these climate models; due to an increase in ambient temperature, the proportion of hourly temperatures that fall within the preferred body temperature range will increase. If snake body temperature were to increase as the climate warms, a theoretical increase in body temperature of 1 and 2°C would have a low impact on the overall energetic needs of snakes, still allowing them to meet baseline maintenance energetic needs with only one large meal a year. Furthermore, we expect small increases in ambient temperature to have little impact on rattlesnakes because they are fairly precise thermoregulators, maintaining fairly constant body temperatures regardless of their thermal surroundings. Overall, our results show that studying the thermal ecology of multiple populations of a single species can reveal fine-scale information about the relationship between the thermal landscape and both ectotherm behavior and physiological processes. Additionally, our findings show that some species of large-bodied reptiles may be robust to modest thermal perturbations under conservative climate change predictions.

Made available in DSpace on 2014-12-17T15:36:35Z (GMT). No. of bitstreams: 1 LeonardoBR_TESE_Cap_II_III.pdf: 677404 bytes, checksum: 247b1251f8d1d16cb41bf4f8ec2f3c18 (MD5) Previous issue date: 2010-03-19 / Universidade Federal do Rio Grande do Norte / This study evaluated the spatial, time and alimentary niches of Tropidurus hispidus and Tropidurus semitaeniatus in sympatry in a caatinga of Rio Grande do Norte, Brazil, as well as their foraging and termoregulatory behaviors, the activity body temperature and their reproductive and fat body cycles. Monthly excursions, from October 2006 to May 2008, were conducted at the Ecological Station of the Serid? (ESEC Serid?), Serra Negra do Norte municipality, using specific methodology for investigation of the aforementioned objectives. The two species presented similarities in space niche use, mainly in rocky habitat, however they differed in vertical microhabitat use with T. hispidus using a larger vertical microhabitat range. In the dry season the time of activity of both species was bimodal. In the wet season T. semitaeniatus showed a unimodal activity period, while T. hispidus maintained an bimodal activity period. In terms of importance in the diet, to both species, Hymenoptera/Formicidae and Isoptera predominated during the dry season. In the wet season, although Hymenoptera/Formicidae had larger importance among the prey items, lizards opportunistically predated on Lepidoptera larvae, Coleoptera larvae/adults and Orthoptera nymphs/adults. The foraging intensity revealed differences between the species, mainly in the wet season, when T. semitaeniatus was more active than T. hispidus. The mean activity body temperature of T. semitaeniatus was significantly higher than that of T. hispidus. The thermoregulatory behavior showed that during the dry season T. hispidus and T. semitaeniatus spent more time in shade or under filtered sun. In the wet season, T. hispidus did not show differences in the amount of time spent among the light exposure locations, however T. semitaeniatus spent most of their time exposed to direct sun or filtered sun. The reproductive cicle of T. hispidus and T. semitaeniatus occurred from the middle of the dry season to the beginning of the wet season. In both species, female reproductive activity was influenced by precipitation, whereas males exhibited spermatozoa in their testes throughout the year, and their reproductive activity was not related with any of the climatic variables analysed. In the two species, the fat storage varied inversely with reproductive activity, and there was no difference in fat body mass between females and males. We concluded that the segregation between T. hispidus and T. semitaeniatus in this caatinga area occurs in vertical space use, in the largest vagility of T. hispidus in microhabitat use and larger range size of their alimentary xviii items. Additionally, significant seasonal differences in relation to the activity period, body temperature, and foraging and termoregulatory behaviors between these two Tropidurus species facilitate their coexistence. / Este estudo avaliou o uso dos recursos espacial, temporal e alimentar por Tropidurus hispidus e Tropidurus semitaeniatus em simpatria em uma caatinga do Rio Grande do Norte, Brasil, bem como seus comportamentos de forrageamento e termorregulat?rio, suas temperaturas corp?reas em atividade e seus ciclos reprodutivos e de gordura corp?rea. Excurs?es mensais, de outubro de 2006 a maio de 2008, foram realizadas ? Esta??o Ecol?gica do Serid? (ESEC Serid?), munic?pio de Serra Negra do Norte, com utiliza??o de metodologia espec?fica para a investiga??o dos objetivos acima mencionados. As duas esp?cies apresentaram similaridades no uso do nicho espacial, especialmente no h?bitat rochoso; contudo, elas diferiram no uso vertical do micro-h?bitat com T. hispidus usando uma faixa vertical maior do micro-h?bitat. Na esta??o seca o per?odo de atividade de ambas as esp?cies foi bimodal. Na esta??o chuvosa, a atividade de T. semitaeniatus mostrou um per?odo unimodal, enquanto T. hispidus manteve uma atividade bimodal. Em termos de import?ncia na dieta, para ambas as esp?cies, os Hymenoptera/Formicidae e Isoptera predominaram na esta??o seca. Na esta??o chuvosa ainda que os Hymenoptera/Formicidae continuaram a ter maior import?ncia entre os itens alimentares, os lagartos predaram oportunisticamente larvas de Lepidoptera, larvas/adultos de Coleoptera e ninfas/adultos de Orthoptera. A medida de intensidade de forrageamento revelou diferen?as entre as esp?cies, especialmente na esta??o chuvosa, quando T. semitaeniatus foi mais ativo do que T. hispidus. A temperatura corp?rea m?dia em atividade de T. semitaeniatus foi significativamente superior a de T. hispidus. O comportamento termorregulat?rio mostrou que, durante a esta??o seca, T. hispidus e T. semitaeniatus gastaram mais tempo expostos ? sombra ou sob sol filtrado. Na esta??o chuvosa, T. hispidus n?o mostrou diferen?as no tempo gasto entre os locais de exposi??o ? luz, contudo T. semitaeniatus esteve a maior parte de seu tempo exposto ao sol ou sob sol filtrado. A reprodu??o de T. hispidus e T. semitaeniatus ocorreu entre a metade da esta??o seca e o in?cio da esta??o chuvosa. Em ambas as esp?cies, a atividade reprodutiva das f?meas foi influenciada pela precipita??o, enquanto os machos apresentaram espermatoz?ides nos test?culos ao longo de todo o ano, e sua atividade reprodutiva n?o foi relacionada com nenhuma das vari?veis clim?ticas analisadas. O estoque de gordura corp?rea variou inversamente com a atividade reprodutiva nas duas esp?cies, e n?o houve diferen?a entre f?meas e machos quanto a massa dos corpos adiposos. Conclu?mos que xvi a segrega??o entre T. hispidus e T. semitaeniatus nesta ?rea de caatinga ocorre no uso vertical do espa?o, na maior vagilidade de T. hispidus na utiliza??o de micro-h?bitats e maior amplitude de tamanho de seus itens alimentares. Adicionalmente, diferen?as sazonais significativas em rela??o ao per?odo de atividade, temperatura corp?rea, e comportamentos de forrageamento e termorregulat?rio entre essas duas esp?cies de Tropidurus, possibilitam a coexist?ncia.