Living in sympatry: The effect of habitat partitioning on the thermoregulation of three Mediterranean lizards

The ability for effective, accurate and precise thermoregulation is of paramount importance for ectotherms. Sympatric lizards often partition their niche and select different microhabitats. These microhabitats, however, usually differ in their thermal conditions and lizards have to adapt their thermoregulation behavior accordingly. Here, we evaluated the impact of habitat partitioning on the thermal biology of three syntopic, congeneric lacertids (Podarcis peloponnesiacus, P. tauricus and P. muralis) from central Peloponnese, Greece. We assessed thermoregulation effectiveness (E) using the three standard thermal parameters: body (T_b), operative (T_e) and preferred (T_pref) temperatures. We hypothesized that the microhabitats used by each species would differ in thermal quality. We also predicted that all species would effectively thermoregulate, as they inhabit a thermally challenging mountain habitat. As expected, the partition of the habitat had an effect on the thermoregulation of lizards since microhabitats had different thermal qualities. All three species were effective and accurate thermoregulators but one of them achieved smaller E values as a result of the lower T_b in the field. This discrepancy could be attributed to the cooler (but more benign) thermal microhabitats that this species occupies.     

Behavioural thermoregulation by the endangered crocodile lizard (Shinisaurus crocodilurus) in captivity

Understanding the factors that may affect behavioural thermoregulation of endangered reptiles is important for their conservation because thermoregulation determines body temperatures and in turn physiological functions of these ectotherms. Here we measured seasonal variation in operative environmental temperature (T_e), body temperature (T_b), and microhabitat use of endangered crocodile lizards (Shinisaurus crocodilurus) from a captive population, within open and shaded enclosures, to understand how they respond to thermally challenging environments. T_e was higher in open enclosures than in shaded enclosures. The T_b of lizards differed between the open and shaded enclosures in summer and autumn, but not in spring. In summer, crocodile lizards stayed in the water to avoid overheating, whereas in autumn, crocodile lizards perched on branches seeking optimal thermal environments. Crocodile lizards showed higher thermoregulatory effectiveness in open enclosures (with low thermal quality) than in shaded enclosures. Our study suggests that the crocodile lizard is capable of behavioural thermoregulation via microhabitat selection, although overall, it is not an effective thermoregulator. Therefore, maintaining diverse thermal environments in natural habitats for behavioural thermoregulation is an essential measure to conserve this endangered species both in the field and captivity.     

Diel and seasonal variations in the thermal biology of San Cristobal Lava Lizards (Microlophus bivittatus)

Thermal biology, and therefore energy acquisition and survival, of ectotherms can be affected by diel and seasonal patterns of environmental temperatures. Galápagos Lava Lizards live in seasonal environments that are characterized by a warm and wet period when reproductive activity is maximal, and cooler and drier period. With the use of radiotelemetric techniques to record lizard surface temperatures (T_s), we studied the thermal ecology of the San Cristóbal Lava Lizard (Microlophus bivittatus) during both the warm and cool seasons over two years. During the diel activity period and when operative temperatures exceeded T_set-min, at least on rock faces without canopy, 52% or less of the T_s observations fell within the laboratory-determined T_set range (36–40 °C). Therefore, lizards may have avoided very warm midday temperatures in shaded microhabitats and the lag times in changes in T_s values occurred as operative temperatures rose rapidly during late morning warming phase. Lizards effectively thermoregulated during a year with moderate warm season temperatures and during a cool season that was unseasonably warm. In contrast, lizards less effectively thermoregulated during the warmest and coolest years of the study. We did not detect intersexual differences in thermoregulation although males may thermoregulate less effectively than do females during the cool season although we were unable to detect significant differences using our nonparametric statistical techniques.     

The peak of thermoregulation effectiveness: Thermal biology of the Pyrenean rock lizard,Iberolacerta bonnali (Squamata,Lacertidae)

We studied, at 2200 m altitude, the thermal biology of the Pyrenean rock lizard, Iberolacerta bonnali, in the glacial cirque of Cotatuero (National Park of Ordesa, Huesca, Spain). The preferred thermal range (PTR) of I. bonnali indicates that it is a cold-adapted ectotherm with a narrow PTR (29.20–32.77 °C). However, its PTR (3.57 °C) is twice as wide as other Iberolacerta lizards, which may be explained by its broader historical distribution. The studied area is formed by a mosaic of microhabitats which offer different operative temperatures, so that lizards have, throughout their entire daily period of activity, the opportunity to choose the most thermally suitable substrates. I. bonnali achieves an effectiveness of thermoregulation of 0.95, which makes it the highest value found to date among the Lacertidae, and one of the highest among lizards. Their relatively wide distribution, their wider PTR, and their excellent ability of thermoregulation, would make I. bonnali lizards less vulnerable to climate change than other species of Iberolacerta. Thanks to its difficult access, the studied area is not visited by a large number of tourists, as are other areas of the National Park. Thus, it is a key area for the conservation of the Pyrenean rock lizard. By shuttling between suitable microhabitats, lizards achieve suitable body temperatures during all day. However, such thermally suitable microhabitats should vary in other traits than thermal quality, such as prey availability or predation risk. Hence, it seems that these not-thermal traits are not constraining habitat selection and thermoregulation in this population. Therefore, future research in this population may study the causes that would lead lizards to prioritize thermoregulation to such extent in this population.     

Thyroxine affects behavioral thermoregulation but not growth rate among populations of the western fence lizard (Sceloporus occidentalis)

We investigated whether thyroxine influences hatchling growth rate of the western fence lizard (Sceloporus occidentalis) throught its effects on thermoregulatory behaviors. We reared control and thyroxine-injected hatchlings from three populations of S. occidentalis that differ in growth rate in a thermal gradient. We also measured the daily changes in body temperature and activity level (proportion of time spent out of retreat sites) of control and thyroxine-injected lizards. Previous studies have shown that within and among population differences in growth rate of the western fence lizard are correlated with the maintenance of high activity levels (proportion of time spent outside of retreat sites) and high body temperatures throughout the day. Growth rate was not influenced by injections of thyroxine. However, injections of thyroxine did elevate average daily body temperature and daily activity. Although administration of thyroxine uniformly increased the probability of activity throughout the day, it did not appear to alter the daily changes in activity. Previous studies have shown that the slower-growing hatchlings from northern populations exhibit a decline in activity during the later part of the thermal cycle, whereas the faster growing southern hatchlings maintain the same level of high activity throughout the thermal cycle. The decline in activity of northern populations was not prevented by thyroxine injection used in our current study. Northern lizards receiving exogenous thyroxine were still less active later in the day compared to early in the day, even though activity level throughout the day was elevated. Thus, the effects of thyroxine on temperature regulation observed in our study (general increase in activity level) appear to be unrelated to those aspects of temperature regulation (e.g., daily changes in behavioral thermoregulation) that are correlated with among population differences in growth rate. We also raised hatchlings in a cycling thermal regime (forced thermal cycle of 34°C:15°C, 12L:12D) where behavioral thermoregulation is not possible. The growth rate of lizards forced to cycle between 34°C:15°C on a daily basis was significantly lower than those lizards allowed to behaviorally thermoregulate, further underscoring the importance of the circadian pattern of thermoregulation for growth.Abbreviations GR growth rate - MR metabolic rate - SMR standard metabolic rate - SVL snout-vent length - T₄ thyroxine - T _b body temperature - T _e environmental temperature     

Habitat use and activity influence thermoregulation in a tropical lizard, Ameiva exsul

We examined the contributions of alterations in daily activity and behavioral selection of microhabitat to thermoregulation in a population of the lizard, Ameiva exsul (Teiidae), by combining data on lizard activity with data on the availability of sun-shade patches and operative temperatures (T_e). By comparing T_e distributions predicted by “no thermoregulation” and “only thermoregulation” hypotheses to those predicted by random use of thermal habitat, we assessed the relative contributions of microhabitat selection and daily activity to regulation of body temperature (T_b). Over the course of a day lizards maintained T_b very close to optimal temperature (T_sel) despite T_es that deviated substantially from T_sel. Data demonstrating a unimodal daily activity pattern reject the hypothesis of uniform activity throughout the day. Also, lizard activity was not positively correlated with the proportion of T_es within T_sel nor negatively correlated with the absolute deviation of available T_e from T_sel (d_e) (“only thermoregulation”). Microsite use by A. exsul deviated significantly from predictions of the “no thermoregulation” hypothesis, but our data could not reject predictions of the “only thermoregulation” hypothesis that lizards would use sun-shade patches relative to the proportion of microsites where T_e is within T_sel. Also, lizards appeared to actively select sunlit and partially shaded microsites at different times of day. Thus, despite thermal constraints imposed by the habitat, A. exsul maintained high and relatively constant T_bs throughout its daily activity period and thermoregulated effectively. This appears to be generally representative of West Indian species of Ameiva.     

Evaluating thermal resource partitioning

Summary The field thermal biology of sympatric Anolis cooki and A. cristatellus were evaluated in January and in August in desert scrub forest at Playa de Tamarindo near Guanica, Puerto Rico. Data on randomly positioned copper models of lizards, each equipped with a built-in thermocouple, established null hypotheses about basking frequency and operative temperatures (T _e) against which the behavior and body temperatures (T _b) of live lizards were evaluated. Both species exhibited non-random hourly basking rates (more marked in cristatellus than in cooki), and cristatellus was virtually inactive during the warm mid-day hours. The relationship between lizards' T _b and randomly sampled T _e differed between the species: cristatellus's mean T _b was 2° to 3° C lower than randomly sampled mean T _e in both months, whereas cooki's mean T _b was slightly higher than mean T _e in January and slightly lower in August. Although cooki's mean T _b was higher than that of cristatellus in both months, the T _b's of the two species overlapped substantially over an annual cycle. Given the similarities in their field active T _b and the low thermal heterogeneity among microsites at Playa de Tamarindo, these species appear not to partition the thermal environment there in a coarse-grained way. Instead, the relatively small differences in their field active T _b probably result from small differences in their use of similar microhabitats within their mutually exclusive territories. Thermal resource partitioning by territorial animals is unlikely unless thermal heterogeneity is coarse-grained in relation to territory size.     

The effects of thermal biology and refuge availability on the restricted distribution of an alpine lizard

Aim In an effort to disentangle the ecological processes that confine ectotherms to alpine environments, we studied the thermoregulatory and microhabitat selection behaviours of the rock lizard Iberolacerta cyreni, which is endemic to some mountains of central Spain, and of the wall lizard Podarcis muralis, which is a potential competitor of rock lizards. Location We chose three areas in the Sierra de Guadarrama (central Spain) that differed in their thermal quality [mean deviation of environmental operative temperatures from the lizards’ preferred thermal range (PTR)] and refuge availability: a pine forest (1770 m a.s.l.) in which P. muralis was the only species found, and two mixed shrub and rock sites (1770 and 1900 m a.s.l.) where both species were present. Methods In the field we collected data on refuge availability, sun exposure, body temperature (T_b) and operative temperature (T_e). Thus, we estimated the thermal habitat quality of the areas sampled and the thermoregulation accuracy and effectiveness of both species. Results The pine forest had the lowest thermal quality and refuge availability. The lower‐elevation shrub site offered the best thermal quality, but refuges were much scarcer than at the higher‐elevation site. Both species thermoregulated accurately, because mean deviations of body temperature (T_b) from PTR were considerably smaller than those of T_e. Podarcis muralis had higher T_b values than did I. cyreni, which had similar T_b values at both shrub sites, whereas P. muralis had lower T_b values at higher elevation. Overall, the thermoregulatory effectiveness (extent to which T_b values are closer to the PTR than are T_e values) of both species was similar, but whereas I. cyreni thermoregulated more efficiently at higher elevation, the opposite was true for P. muralis. At the lower‐elevation shrub site, I. cyreni remained closer to refuges than did P. muralis. Main conclusions Our results suggest that the pine forest belt might prevent the expansion of rock lizards towards lower elevations as a result of its low thermal quality and scarcity of refuges, that the thermoregulatory effectiveness of rock lizards in alpine environments depends more on refuge availability than on thermal habitat quality, and that competition with wall lizards is unlikely to explain either the distribution or the thermoregulatory effectiveness of rock lizards.     

Daily and annual patterns of thermoregulation in painted turtles (Chrysemys picta marginata) living in a thermally variable marsh in Northern Michigan

The capacity for an ectothermic reptile to thermoregulate has implications for many components of its life history. Over two years, we studied thermoregulation in a population of Midland painted turtles (Chrysemys picta marginata) in a shallow, thermally variable wetland during summer in Northern Michigan. Mean body temperature (T_b) of free-ranging turtles was greater in 2008 (25.8 °C) than in 2010 (19.7 °C). Laboratory determined thermoregulatory set point (T_set) ranged from 25 °C (T_set-min) to 31 °C (T_set-max) and was lower during the fall (17–26 °C). Deviations of T_b distributions from field measured operative temperatures (T_e) and indices of thermoregulation indicated that C. picta marginata were capable of a limited degree of thermoregulation. Operative temperatures and thermal quality (d_e=|T_set-min−T_e| and |T_e−T_set-max|) cycled daily with maximal thermal quality occurring during late morning and late afternoon. The accuracy of thermoregulation (d_b=|T_set-min−T_b| and |T_b−T_set-max|) was maximal (d_b values were minimal) as T_b declined and traversed T_set during the late afternoon–early evening hours and was higher on cloudy days than on sunny days because relatively low T_e values decreased the number of T_b values that were above T_set. Our index of thermal exploitation (E_x=frequency of T_b observations within T_set) was 36%, slightly lower than that reported for an Ontario population of C. picta marginata. Regression of d_b (thermal accuracy) on d_e (thermal quality) indicated that turtles invested more in thermoregulation when thermal quality was low and when water levels were high than when they were low. There were no intersexual differences in mean T_b throughout the year but females had relatively high laboratory determined T_b values in the fall, perhaps reflecting the importance of maintaining ovarian development prior to winter.     

Influences of sex,ontogeny and body size on the thermal ecology of Liolaemus lutzae (Squamata,Liolaemidae) in a restinga remnant in southeastern Brazil

Variations in body temperature (T_b) of lizards can be partially explained by intrinsic factors such as sex, ontogeny and body size. Liolaemus lutzae is a lizard species restricted to restingas in the Brazilian coast in the state of Rio de Janeiro. Herein, we studied sexual dimorphism and influences of sex, ontogeny, and body size to the T_b of L. lutzae. Adult males were larger than adult females, probably due to both intersexual selection and intra-sexual selection. There was intersexual difference in lizards' T_b (males hotter than females), but T_b did not differ after factored out for the effects of body size. The mean T_b of juvenile lizards was higher than that of adults after factored out for the effect of body mass. It is possible that adults may have excluded juveniles from microhabitats with better thermal regimes. Also, this might have occurred due to requirements of juveniles to maintain high growth rates. Forage searching for prey by juveniles also exposes them to high environmental temperatures. Juveniles also may have higher T_b than co-specific adults (relative to body mass) to favor prey capture. In absolute values, adult lizards tended to use microhabitats with lower temperatures than that used by juveniles, possibly to avoid risks of overheating and death. Body temperature and snout–vent length were positively related, as well as body temperature and body mass, presumably caused by the thermal inertia of the bodies (trend of a body to resist to changes in its temperature). Intrinsic factors such as sex, ontogeny and body size can affect the thermal ecology of L. lutzae, despite coastal habitat features to which they are exposed also influences the body temperature of active lizards in restinga habitats.     

Lizards on ice: Comparative thermal tolerances of the world's southernmost gecko

(1) We measured thermal tolerances (critical thermal minimum, CT_min and panting threshold, T_pant) for four populations of Homonota darwinii spanning most of the latitudinal range of the species. (2) CT_min differed across populations, but not latitudinally as predicted, likely because latitude was not as good a proxy for operative temperatures (T_e). (3) Some populations had subzero CT_min indicating supercooling or freeze tolerance—the first time either phenomenon has been reported for a gecko. (4) T_pant did not differ significantly among populations. (5) The thermal tolerance breadth appears to be correlated with thermal variability in the environment. (6) Annual T_e data indicate gecko retreats play a crucial role in surviving extreme surface temperatures (<0 or >50 °C).     

Latitudinal comparison of the thermal biology in the endemic lizard Liolaemus multimaculatus

Thermoregulation in ectotherms may be modulated by climatic variability across geographic gradients. Environmental temperature varies along latitudinal clines resulting in heterogeneous thermal resource availability, which generally induces ectotherms to use compensatory mechanisms to thermoregulate. Lizards can accommodate to ambient temperature changes through a combination of adaptive evolution and behavioral and physiological plasticity. We studied the thermal ecology of the endangered endemic lizard Liolaemus multimaculatus at six different sites distributed from the northern to southern areas of the distribution (700 km) in the Atlantic dune barriers of Argentina, and even including the borders areas of the distribution range. Environmental temperatures and relative humidity showed a strong contrast between northern and southern limits of the distribution range. The northern localities had operative temperatures (Te) above the range of preferred temperatures (Tset), instead, the southern localities had large proportion of Tes within the Tset. Although these different climatic conditions may constrain the thermal biology of L. multimaculatus, individuals from all localities maintained relatively similar field body temperatures (XTb = 34.07 ± 3.02 °C), suggesting that this parameter is conservative. Thermal preference partially reflected latitudinal temperature gradient, since lizards from the two southernmost localities showed the lowest Tsel and Tset. Thermoregulatory efficiency differed among localities, since E values in the northern localities (E = 0.53–0.69) showed less variability than those of southern localities (E = 0.14–0.67). Although L. multimaculatus employed a strategy of having a conservative Tb and being able to acclimatize the thermal preference to copes with latitudinal changes in the thermal environment, other local factors, such as ecological interactions, may also impose limitations to thermoregulation and this may interfered in the interpretation of results at wider spatial scale.     

Facing the Heat: Thermoregulation and Behaviour of Lowland Species of a Cold-Dwelling Butterfly Genus,Erebia

Understanding the potential of animals to immediately respond to changing temperatures is imperative for predicting the effects of climate change on biodiversity. Ectothermic animals, such as insects, use behavioural thermoregulation to keep their body temperature within suitable limits. It may be particularly important at warm margins of species occurrence, where populations are sensitive to increasing air temperatures. In the field, we studied thermal requirements and behavioural thermoregulation in low-altitude populations of the Satyrinae butterflies Erebia aethiops, E. euryale and E. medusa. We compared the relationship of individual body temperature with air and microhabitat temperatures for the low-altitude Erebia species to our data on seven mountain species, including a high-altitude population of E. euryale, studied in the Alps. We found that the grassland butterfly E. medusa was well adapted to the warm lowland climate and it was active under the highest air temperatures and kept the highest body temperature of all species. Contrarily, the woodland species, E. aethiops and a low-altitude population of E. euryale, kept lower body temperatures and did not search for warm microclimates as much as other species. Furthermore, temperature-dependence of daily activities also differed between the three low-altitude and the mountain species. Lastly, the different responses to ambient temperature between the low- and high-altitude populations of E. euryale suggest possible local adaptations to different climates. We highlight the importance of habitat heterogeneity for long-term species survival, because it is expected to buffer climate change consequences by providing a variety of microclimates, which can be actively explored by adults. Alpine species can take advantage of warm microclimates, while low-altitude grassland species may retreat to colder microhabitats to escape heat, if needed. However, we conclude that lowland populations of woodland species may be more severely threatened by climate warming because of the unavailability of relatively colder microclimates.     

Thermal Preference of the Bush Cricket <Emphasis Type="Italic">Isophya rizeensis</Emphasis>; Testing the Effect of Countergradient Selection

Thermal preference is one of the most crucial components of behavioral thermoregulation in ectotherms, and documenting the adaptation of thermal preference carries great importance for studying the evolution of thermal biology. However there are not many studies focusing on the adaptation of thermal preference in elevational and latitudinal gradients. Isophya rizeensis is a color polymorphic bush cricket species endemic to the mountainous region of northeastern Turkey. Populations of this species are distributed in a wide elevational range between 350 and 2300 m. In this study, we hypothesized that the thermal preference of Isophya rizeensis might follow a countergradient variation where crickets from higher altitudes have higher temperature preferences compared to crickets from lower altitudes. To test this hypothesis, thermal preference values (T _pref ) of crickets from three altitudes groups (low, middle and high) were measured with a thermal gradient experiment. Additionally, body temperatures (T _b ) and environmental temperatures (T _a ) were measured in field. Deviation values of T _b and T _a from T _pref were calculated to investigate the extent of thermoregulation. As Isophya rizeensis is color polymorphic species where morphology pattern changes from lighter to darker types with increasing altitude we also tested whether coloration has any effect on temperature excess (T _ex ) and thermoregulation. Thermal preference values did not differ significantly between three groups and also colouration does not influence the extent of thermoregulation in this species. These results indicate that there is not sufficient evidence for the existence of a countergradient selection related with thermal behavior. However, the deviation of body (D _b ) and environmental (D _a ) temperatures suggest that at higher altitudes thermoregulation might be more efficient than lower altitudes.     

EVOLUTIONARY PATTERNS OF THE THERMAL SENSITIVITY OF SPRINT SPEED IN ANOLIS LIZARDS

I present evidence that the thermal sensitivity of sprint speed of Anolis lizards has evolved to match the activity body temperatures (T_b) experienced by local populations in nature. Anolis lizards from a range of altitudes in Costa Rica have limited thermoregulatory abilities and consequently have field T_b that differ substantially in median and interquartile distance (a measure of variability). Experimentally determined maximal sprint temperatures (T_b at which lizards run fastest) were positively correlated with median field T_b, and performance breadths (ranges of T_b over which lizards run well) were correlated with the variability (interquartile distance) of field T_b in the species I examined. Such correlations would be expected if the thermal sensitivity of sprint speed and field T_b had evolved together to improve the sprint performance of lizards in nature. Integration of laboratory and field studies indicates that several species of Anolis regularly experience impaired sprint speeds in the field, despite apparent evolutionary modification of their thermal physiologies. However, this impairment would have been more severe if the thermal sensitivities of sprint speed had not evolved. Data from other groups of lizards indicate that the thermal sensitivity of sprint speed has not evolved to match T_b of local populations (Hertz et al., 1983; Crowley, 1985). These lizards experience less variable T_b and less impairment of sprint speeds in the field than do the anoles. Thus, selection for modification of the thermal sensitivity of sprint speed might have been stronger for anoles than for other groups of lizards.     

Effects on the thermoregulatory efficiency of two native lizards as a consequence of the habitat modification by the introduction of the exotic tree Acacia longifolia

Habitat modification alters several aspects of the original fauna, among them the opportunity for thermoregulation. Here, we studied the thermal biology of sympatric populations of two lizard species (Liolaemus multimaculatus and Liolaemus wiegmannii) in two different situations; a grassland without trees (natural habitat) and in a grassland plus the exotic tree Acacia longifolia (modified habitat), aiming to assess whether the structural alteration of native Pampean coastal grasslands of Argentina affects the thermal biology of these lizards. Field body temperatures, laboratory preferred temperatures, micro-environmental temperatures, operative temperatures, thermoregulatory efficiency and spatial distribution of each species were analyzed in both habitats. Environmental operative temperature was 0.64 °C lower in the modified habitat (Te=38.39 °C) than in the natural (Te=39.03 °C). Thermoregulatory efficiency (E) of L. wiegmannii was lower in modified sites (E=0.58) than in natural sites (E=0.70). This difference may be because this lizard occupied shaded microhabitats under acacias, with suboptimal thermal features. In contrast, L. multimaculatus in the modified habitat restricted its activity to open microenvironments that retained a similar structure to that of the native habitat, while maintaining high thermoregulatory efficiency in both habitat types (E_modified=0.92; E_natural=0.96). Although these two lizard species are phylogenetically close, they respond differently to human-induced changes in their thermal environments. The introduction of A. longifolia into coastal grasslands for L. wiegmannii in particular, this introduction converts its native habitat into a suboptimal thermal environment.     

Miami heat: Urban heat islands influence the thermal suitability of habitats for ectotherms

The urban heat island effect, where urban areas exhibit higher temperatures than less‐developed suburban and natural habitats, occurs in cities across the globe and is well understood from a physical perspective and at broad spatial scales. However, very little is known about how thermal variation caused by urbanization influences the ability of organisms to live in cities. Ectotherms are sensitive to environmental changes that affect thermal conditions, and therefore, increased urban temperatures may pose significant challenges to thermoregulation and alter temperature‐dependent activity. To evaluate whether these changes to the thermal environment affect the persistence and dispersal of ectothermic species in urban areas, we studied two species of Anolis lizards (Anolis cristatellus and Anolis sagrei) introduced to Miami‐Dade County, FL, USA, where they occur in both urban and natural habitats. We calculated canopy openness and measured operative temperature (T_e), which estimates the distribution of body temperatures in a non‐thermoregulating population, in four urban and four natural sites. We also captured lizards throughout the day and recorded their internal body temperature (T_b). We found that urban areas had more open canopies and higher T_e compared to natural habitats. Laboratory trials showed that A. cristatellus preferred lower temperatures than A. sagrei. Urban sites currently occupied by each species appear to lower thermoregulatory costs for both species, but only A. sagreihad field T_b that were more often within their preferred temperature range in urban habitats compared to natural areas. Furthermore, based on available T_e within each species' preferred temperature range, urban sites with only A. sagrei appear less suitable for A. cristatellus, whereas natural sites with only A. cristatellus are less suitable for A. sagrei. These results highlight how the thermal properties of urban areas contribute to patterns of persistence and dispersal, particularly relevant for studying species invasions worldwide.     

Effect of altitude on thermal responses of Liolaemus pictus argentinus in Argentina

Reptiles that live in cooler environments hibernate longer and, when active, limit daily activity times, allocate more time and energy toward thermoregulation, and consequently experience life-history constraints such as reduced fecundity and supra-annual reproductive cycles. This pattern becomes more extreme with increasing latitude and altitude. We compared the thermal biology of two populations of Liolaemus pictus argentinus living at two altitudes (771 and ∼1700 m asl). Environmental, microenvironmental, and operative temperatures were studied in order to describe the capture sites, sources of heat, and availability of microenvironments appropriate for thermoregulation. The body temperatures of L. p. argentinus at capture (T_b) and the preferred temperatures in the laboratory (T_p) were recorded and integrated with operative temperatures to calculate the effectiveness of thermoregulation. The high-altitude population was found to have a lower mean T_b (29 °C compared to 33 °C), while the T_p values for both populations were similar (36.7 °C). The analysis of operative temperatures and T_b in relation to T_p showed that L. p. argentinus behaves as a moderate thermoregulator at high altitude and as a poor thermoregulator at the low-altitude site probably due in part to the avoidance of predation risk.     

Effects of hypoxia on the thermal physiology of a high-elevation lizard: implications for upslope-shifting species

Montane reptiles are predicted to move to higher elevations in response to climate warming. However, whether upwards-shifting reptiles will be physiologically constrained by hypoxia at higher elevations remains unknown. We investigated the effects of hypoxic conditions on preferred body temperatures (T_pref) and thermal tolerance capacity of a montane lizard (Phrynocephalus vlangalii) from two populations on the Qinghai–Tibet Plateau. Lizards from 2600 m a.s.l. were exposed to O₂ levels mimicking those at 2600 m (control) and 3600 m (hypoxia treatment). Lizards from 3600 m a.s.l. were exposed to O₂ levels mimicking those at 3600 m (control) and 4600 m (hypoxia treatment). The T_pref did not differ between the control and hypoxia treatments in lizards from 2600 m. However, lizards from 3600 m selected lower body temperatures when exposed to the hypoxia treatment mimicking the O₂ level at 4600 m. Additionally, the hypoxia treatment induced lower critical thermal minimum (CT_min) in lizards from both populations, but did not affect the critical thermal maximum (CT_max) in either population. Our results imply that upwards-shifting reptiles may be constrained by hypoxia if a decrease in T_pref reduces thermally dependent fitness traits, despite no observed effect on their heat tolerance.     

Effects of temperature and elevation on habitat use by a rare mountain butterfly: implications for species responses to climate change

Abstract 1. The present study used the mountain specialist butterfly Parnassius apollo as a model system to investigate how climate change may alter habitat requirements for species at their warm range margins. 2. Larval habitat use was recorded in six P. apollo populations over a 700 m elevation gradient in the Sierra de Guadarrama (central Spain). Larvae used four potential host species (Sedum spp.) growing in open areas amongst shrubs. 3. Parnassius apollo host‐plant and habitat use changed as elevation increased: the primary host shifted from Sedum amplexicaule to Sedum brevifolium, and larvae selected more open microhabitats (increased bare ground and dead vegetation, reduced vegetation height and shrub cover), suggesting that hotter microhabitats are used in cooler environments. 4. Larval microhabitat selection was significantly related to ambient temperature. At temperatures lower than 27 °C, larvae occupied open microhabitats that were warmer than ambient temperature, versus more shaded microhabitats that were cooler than ambient conditions when temperature was higher than 27 °C. 5. Elevational changes in phenology influenced the temperatures experienced by larvae, and could affect local host‐plant favourability. 6. Habitat heterogeneity appears to play an important role in P. apollo larval thermoregulation, and may become increasingly important in buffering populations of this and other insect species against climatic variation.