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Frontiers in Amphibian and Reptile Science ·

Volume 4 - 2026 | https://doi.org/10.3389/famrs.2026.1758509

Ecophysiology and vulnerability to warming of Whorl-tail Iguanas (Tropidurinae: Stenocercus) from the Tropical Andes of Ecuador

  • Estefany S. Guerra-Correa1,2*corresponding author
  • Juan M. Guayasamin2,3
  • Richard A. Peters1
  1. 1Animal Behaviour Group, La Trobe University, Melbourne, VIC, Australia
  2. 2Laboratorio de Biología Evolutiva, Colegio de Ciencias Biológicas y Ambientales, Universidad San Francisco de Quito, Cumbayá, Quito, Ecuador
  3. 3Galapagos Science Center, Universidad San Francisco de Quito (USFQ) and University of North Carolina at Chapel Hill, Puerto Baquerizo Moreno, Ecuador
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Abstract

Environmental changes can significantly affect the performance of ectotherms, as nearly all aspects of their life history are intricately linked to temperature conditions in their habitats. One approach to quantify ectothermic physiological performance is to assess traits that define their thermal tolerance. Research integrating thermophysiological traits of terrestrial ectotherms with environmental data has shown that tropical ectothermic species face a higher risk of extinction compared to their temperate counterparts because they live near their physiological thermal optimum and exhibit limited plasticity to adapt to changing conditions. In this study we measured the preferred body temperature (T pref), critical thermal minimum (CT min), and critical thermal maximum (CT max) of seven Stenocercus populations inhabiting high-altitude tropical ecosystems in the Ecuadorian Andes, between 2093 and 4046 m asl. Field-based experiments were conducted on adult lizards to determine these thermophysiological traits. We combined these data with environmental records and operative temperature models (OTMs) to characterise the thermal conditions of each population's microhabitat and to evaluate vulnerabilty under current and future warming scenarios. Our findings support the hypothesis that habitats with greater daily temperature variability and structurally complex vegetation allow lizards to exhibit broader thermal tolerance ranges and higher tolerance to warming. For instance, Stenocercus lizards from paramo ecosystems are unlikely to be physiologically constrained by projected temperature increases. In contrast, warming is likely to restrict the activity of Inter-Andean lizards because their microhabitats already reach temperatures close to their physiological optimum. These results highlight the importance of access to suitable thermal microhabitats and the role of behavioural strategies in reducing the risk of overheating.

Keywords

1 Introduction

Climate-driven impacts on species vary widely in both direction and magnitude on a global scale (Williams and Jackson, 2007). For most ectothermic species, environmental changes can adversely affect their performance, as nearly all aspects of their life history are closely influenced by temperature conditions in their habitats (Angilletta et al., 2002; Ibargüengoytía et al., 2010; Kubisch et al., 2016; Zhu et al., 2025). One method for quantifying ectothermic physiological responses is to examine their thermal performance curves, which describe how body temperature affects their performance or fitness (Huey and Stevenson, 1979; Huey and Kingsolver, 1989; Kingsolver et al., 2013). In brief, an organism’s thermal performance increases gradually from a critical thermal minimum (CTmin) to an optimal temperature (Topt) and then declines rapidly as body temperature approaches the critical thermal maximum (CTmax) (Angilletta et al., 2002). These thermal traits are traditionally measured in terrestrial ectotherms, revealing geographic patterns of local adaptation and responses to climate variations (Chown and Terblanche, 2007; Kingsolver et al., 2013). For instance, species from higher latitudes typically exhibit greater thermal breadth (the difference between CTmax and CTmin) and lower CTmin values compared to tropical species (Clusella-Trullas et al., 2011; Kingsolver et al., 2013; Sunday et al., 2011).

Several studies have integrated physiological thermal tolerance metrics with environmental data, using correaltive or mechanistic modelling approaches, to predict population declines and local extinctions of ectotherms across latitudinal and elevational gradients (Chen et al., 2011; García-Robledo et al., 2016; Sinervo et al., 2010). Based on these approaches, tropical ectothermic species are often considered at greater risk of extinction than their temperate counterparts because they tend to operate close to their physiological thermal optima and are assumed to have limited physiological and behavioural plasticity (Deutsch et al., 2008; Huey et al., 2009; Morley et al., 2019; Polato et al., 2018). Despite their widespread use, these approaches can yield inaccurate or incomplete predictions, particularly in tropical systems, for three main reasons. First, they commonly rely on ambient air temperature as a proxy for the organismal habitat temperature, overlooking the fact that ectotherms can experience substantially different thermal conditions within their microhabitats (Pincebourde and Suppo, 2016; Potter et al., 2013). Second, tropical environments, are characterised by strong spatial and temporal thermal heterogeneity at fine scales, which can directly influence the thermal physiology and thermoregulatory opportunities of small ectotherms (Pincebourde and Suppo, 2016). Third, much of the empirical support underlying predictions of tropical ectotherm vulnerability, especially in lizards, comes from low- and mid-altitude tropical ecosystems, such as tropical rainforests, resulting in a strong elevational bias (Brusch et al., 2016; Huey et al., 2009; Muñoz et al., 2014, 2022). Consequently, the thermal responses of high-altitude tropical mountain species remain poorly understood, limiting our ability to accurately predict their vulnerability to climate change.

The rapid uplift of the Andes created complex and diverse ecosystems with distinct climate conditions that vary by altitude (Esquerré et al., 2019). High-elevation tropical Andean ecosystems, for example, exhibit steep altitudinal gradients with marked macroclimate variations, which interact with abiotic and biotic factors to create a mosaic of thermal microclimates (Arroyo and Cavieres, 2013; Woods et al., 2015). When first formed, these heterogeneous and fragmented Andean ecosystems provided new habitats for some groups to explosively diversify (Drummond et al., 2012; Hutter et al., 2013; Losos, 2009). This is true for Stenocercus lizards, which inhabit various South American landscapes, including dry and humid tropical forests, montane forests, and paramo, at elevations between 0 and 4000 m asl (Torres-Carvajal, 2000).

Two studies have examined aspects of the thermal biology of high-altitude tropical montane Stenocercus species. Andrango et al. (2016) conducted the first study to model local extinction risks for the Ecuadorian tropical Andean species S. guentheri. By integrating temperatures recorded with physical models placed in various microhabitats (i.e. operative temperature), the species’ preferred body temperature, and air temperatures from weather stations at georeferenced points within the species’ distribution, they predicted that 26.7% of this species’ populations will be extinct by 2050. In the only other study, Guerra-Correa et al. (2020) reported that tropical Andean Stenocercus lizards exploit diverse thermal microenvironments, allowing them shelter and remain active without experiencing thermal stress or reduced performance. Their findings emphasise the importance of microhabitat structure for these species and highlighted the need to investigate additional thermal adaptations, many of which remain poorly understood.

In this study, we aim to examine how vegetation structure and composition combined with local environmental conditions influence key thermophysiological traits of multiple Stenocercus populations from the Ecuadorian Andes, and how these interactions translate into differences in thermal vulnerability. We hypothesise that the interplay between pronounced daily temperature fluctuations, characteristic of high-altitude tropical montane ecosystems, and local vegetation assemblages plays a central role in shaping these lizards’ thermal preferences and tolerances. Specifically, we predict that lizards inhabiting areas with greater daily temperature variability and more complex vegetation structure will exhibit broader thermal tolerance ranges and more flexible thermal preferences than those in areas with lower temperature variability and less vegetative landscapes. This assumption is grounded in the climatic variability hypothesis and theories of phenotypic plasticity, which states that ectotherms inhabiting environments with large diurnal temperature fluctuations and structurally complex microhabitats promote broader thermal physiological responses, especially when coupled with behavioural thermoregulation (Janzen, 1967; Angilletta, 2009; Muñoz and Bodensteiner, 2019). To test these hypotheses, we assessed three thermophysiological traits including the preferred body temperature (Tpref), critical thermal minimum (CTmin) and maximum (CTmax) across six Stenocercus species inhabiting three high-altitude ecosystems. These physiological data were then integrated with climate records and spatially distributed operative temperature models to quantify thermal vulnerability using established indices, including thermal safety margins (TSM) and warming tolerance (WT) under present and future warming scenarios.

2 Methods

2.1 Focal species and collection

Six closely related Stenocercus species inhabiting high-altitude montane ecosystems in the Ecuadorian Andes were evaluated (Figure 1). Stenocercus angel occurs in southern Colombia and northern Ecuador and primarily inhabits high evergreen montane forests, humid montane shrublands, Espeletia-dominated paramos, and highland grasslands at elevations ranging from 2400 to 3875 m asl. Stenocercus chota is restricted to the inter-Andean valleys of northern Ecuador, where it occupies dry highland shrublands and human-disturbed areas between 1574 and 1940 m asl. Stenocercus guentheri, distributed in southern Colombia and northern Ecuador, inhabits both dry and humid ecosystems, including evergreen montane forests, highland shrublands, paramos, and altered landscapes across an elevational range of 2135 to 3890 m asl. In central Ecuador, S. cadlei occurs in inter-Andean valleys across grasslands, croplands, montane forests, shrublands, and paramos at elevations ranging from 1956 to 4024 m asl. Stenocercus festae is distributed in southern Ecuador, inhabiting undisturbed shrub-dominated areas as well as disturbed habitats such as pine plantations, pastures, and rural gardens between 1050 and 3200 m asl. Finally, S. ornatus occurs in inter-Andean basins of southern Ecuador, occupying humid and dry montane shrublands, evergreen high montane forests, paramos, and disturbed areas at elevations between 1500 to 3000 m asl (Torres-Carvajal, 2000, 2007).

*Stenocercus* species included in this study: **(A)***S. angel*, **(B)***S. chota*, **(C)***S. guentheri*, **(D)***S. cadlei*, **(E)***S. festae*, and **(F)***S. ornatus*. Asterisks (*) indicate endemic species.
Figure 1. Stenocercus species included in this study: (A)S. angel, (B)S. chota, (C)S. guentheri, (D)S. cadlei, (E)S. festae, and (F)S. ornatus. Asterisks (*) indicate endemic species.

These species were sampled across seven tropical montane sites distributed along the Ecuadorian Andes, spanning elevations from 2095 to 4046 m asl. To assess intraspecific differences in thermophysiological traits, two S. guentheri populations inhabiting the range margins of this species distribution were included (Figure 2; Table 1). Based on the local-scale plant community composition, study sites were classified into three ecosystem categories: inter-Andean scrubs, high montane evergreen shrublands, and upper montane paramos (Ministerio del Ambiente del Ecuador, 2013) (Figure 3). Inter-Andean scrubs, henceforth inter-Andean, are vegetation formations adapted to prolonged and severe droughts, characterised by low stature trees and spiny plants resistant to long dry seasons and low annual precipitation (Young et al., 2011) (Figures 3A, B). High montane evergreen shrublands, henceforth evergreen, cover a wide range of vegetation types, from woody plant species less than 5 metres in height to epiphytes such as orchids, ferns, and bryophytes (Ministerio del Ambiente del Ecuador, 2013). This vegetation structure creates a low and open canopy that allows high light penetration, supporting relatively high diversity in the herbaceous layer (Ministerio del Ambiente del Ecuador, 2013) (Figures 3C, D). Upper montane paramos, henceforth paramo, are characterised by average temperatures below 10°C, persistent cloud cover, high precipitation, intense UV radiation, low atmospheric pressure, and strong winds. These harsh environmental conditions result in landscapes dominated by grasslands and shrublands with unique adaptations (Ruiz et al., 2011; Young et al., 2011; CEPF, 2021) (Figures 3E–G).

Geographic location of the seven study sites examined in this study, each representing a different *Stenocercus* population in Ecuador.
Figure 2. Geographic location of the seven study sites examined in this study, each representing a different Stenocercus population in Ecuador.

Table 1. Stenocercus species and sampling sites in the Northern Andes of Ecuador.

SpeciesStudy site (Abbreviation name)GPS coordinatesElevation range (m asl)
S. angelEl Angel Ecological Reserve (El Angel ER)0°42′21.866″ N 77°58′56.661″ W3500 – 3685
S. chotaPisquer (Pisquer)0°30′42.296″ N 78°5′5.827″ W2093 – 2235
S. guentheriJerusalem Recreational Park and Protected Forest (Jerusalem RPPF)0°0′29.47″ S 78°21′31.305″ W2193 – 2289
Cotopaxi National Park (Cotopaxi NP)0°36′35.604″ N 78°28′51.718″ W3700 – 3897
S. cadleiChimborazo Wildlife Production Reserve (Chimborazo WPR)1°31′28.409″ S 78°50′44.199″ W3889 – 4046
S. festaeEl Gullan Scientific Station (El Gullan SS)3°20′17.83″ S 79°10′18.195″ W2918 – 3028
S. ornatusMadrigal of Podocarpus Reserve (Madrigal PR)4°2′48.527″ S 79°10′46.714″ W2295 – 2509

Abbreviation names of study sites and ecosystem types in bold will be used in subsequent sections of this article.

Vegetation structure at each study site. **(A)** Pisquer and **(B)** Jerusalem RPPF are in inter-Andean ecosystems; **(C)** Madrigal PR and **(D)** El Gullan SS are part of evergreen ecosystems; and **(E)** Cotopaxi NP, **(F)** Chimborazo WPR, and **(G)** El Angel ER are situated in paramo ecosystems.
Figure 3. Vegetation structure at each study site. (A) Pisquer and (B) Jerusalem RPPF are in inter-Andean ecosystems; (C) Madrigal PR and (D) El Gullan SS are part of evergreen ecosystems; and (E) Cotopaxi NP, (F) Chimborazo WPR, and (G) El Angel ER are situated in paramo ecosystems.

Fieldwork was conducted during eight sampling sessions between June and October in each of the years 2021, 2022, and 2023 (Supplementary Table S1). Sampling took place from 0800 to 1700 hours at each study site, targeting active adult females and males in their habitats using noose-capture techniques. Immediately upon capture, a K-type thermocouple connected to a 51-II Single Input Digital Thermometer (Fluke Corporation) was used to measure the body temperature (Tb) and substrate temperature (Tsub). The thermocouple was inserted into the lizard’s cloaca to measure Tb, while Tsub was measured by placing the thermocouple probe onto the substrate where the lizard was captured. Care was taken to shield individuals from direct sunlight to prevent inaccuracies in Tb measurements. Weather parameters such as air temperature (Tair), wind speed (WS), and relative humidity (RH), were measured immediately upon capture using a Kestrel 3000 meter (Nielsen Kellerman Inc.). Captured lizards were temporarily held in collection bags for transporting to the field base camp for thermophysiological experimentation.

2.2 Thermophysiological experiments

Thermophysiological experiments were conducted at the field base camp at each site to minimise suffering and stress caused by lengthy travel times. Lizards were housed in individual terrariums (28 cm long x 17.5 cm wide x 17 cm high) with ad libitum water for a maximum of three days before being released at each capture site. The experimentation process began with measurements of preferred body temperature (Tpref), followed by assessments of critical thermal minimum (CTmin) and maximum (CTmax), with a 24-hour interval between each experiment to allow the lizard to recover. The sample size for S.festae was smaller than that of the other populations due to unforeseen circumstances encountered during sampling that forced us to stop fieldwork.

For Tpref experiments, a temporary outdoor field enclosure was utilised. Wooden enclosures measuring 1 m long x 0.12 m wide x 0.2 m high were placed on the ground, with a 100-watt light bulb installed at one end to create a thermal gradient (Supplementary Figure S1) (Guerra-Correa et al., 2020; Paranjpe et al., 2012). Body temperatures were recorded in real time using the Omega Logging Recorder program (OMEGA Engineering Inc.) every 30 seconds for 2 hours, with a K-type thermocouple placed anteriorly to the cloacal area and secured with Micropore surgery tape. Lizards were released in the middle of the enclosure at the start of each experiment with a 15-minute period of acclimatation. Tpref was determined by averaging the body temperature recorded for the two hours of experimentation.

For CTmin and CTmax experiments, we built a custom-controlled thermal system capable of increasing or decreasing temperature at a rate of 1.5-2°C per minute. The system consisted of an enclosed experimental chamber in which individual lizards were placed, allowing precise control of ambient temperature while minimising external thermal interference. Temperature within the chamber was continuously monitored using a thermocouple temperature sensor positioned on the thermal system wall, which provided real-time feedback to an Arduino microcontroller. The Arduino board regulated temperature changes by controlling both heating and cooling elements through a solid-state relay (DC 3-32V) and an amplifier transistor mounted on a heatsink to dissipate excess heat and ensure stable power delivery. Cooling was achieved using Peltier cells coupled with cooling fans, which facilitated efficient heat dissipation and prevented thermal accumulation within the system. Heating was provided by a ceramic air heater that delivered uniform warm airflow into the chamber. An adapter converter regulator supplied and stabilised voltage to all electronic components, ensuring consistent system performance. Temperature adjustments were programmed in the Arduino to produce gradual, linear changes at the target rate of 1.5-2°C per minute, reducing thermal shock to the animals. A camera was mounted inside the thermal system to continuously record lizard behaviour during trails, allowing precise identification of loss-of-function endpoints associated with critical thermal minima and maxima (Supplementary Figure S2).

Body temperatures were recorded using the same procedure as in Tpref experiments. CTmin trials concluded when the lizard was unable to right itself after flipping onto its back, while for CTmax, the end of the experiment was determined by the first mouth-opening response exhibited by the lizard. This response, known as panting, is a thermoregulatory mechanism used by lizards to cool their body temperature under heat stress and is typically exhibited before losing their righting response (Clusella-Trullas et al., 2021; Heatwole et al., 1973). All lizards were released at the end of the experimental period.

2.3 Operative temperature models and climate data

Ten operative temperature models (OTMs) were used to measure the available temperatures within the lizards’ microhabitat. These models consisted of 3D-printed lizards connected to a two-channel HOBO Pro V2 U23–003 data logger (Onset Computer Corporation) (Supplementary Figure S3). We followed the 3D digitisation protocol established by Medina et al. (2020) to build 3D lizards from a well-preserved specimen of S. cadlei from the Zoology Museum of Pontificia Universidad Católica del Ecuador (QCAZ). The scanned specimen accurately replicated the shape and the average adult size of the studied Stenocercus species (SVL = 83 mm, body height = 17 mm, body width = 18 mm, tail length = 65 mm) (Behm et al., 2018; Watson and Francis, 2015) (Supplementary Table S2). The 3D lizards were printed using polylactic acid (PLA) in a posture with extended hind and forelimbs and a completely flat ventral surface. PLA is an affordable material for 3D printing and was tested against other materials and shown to have high accuracy in relation to temperature of a live organism in its habitat (Alujević et al., 2024). All models were printed at DLab, Universidad San Francisco de Quito (USFQ), using a MK3S printer (Prusa Research A.S.) with a shell thickness of 1.2 mm, a layer height of 0.16 mm, and an infill density of 10% with a lighting fill pattern (i.e. models were 90% hollow). The 3D-printed lizards were painted with dark brown synthetic paint on the dorsum and pale beige synthetic paint on the belly to match lizards’ colour background. The two external probes of the HOBO Pro V2 U23–003 data logger were inserted 4 cm into the 3D-printed lizards and secure with cloth tape.

The OTMs were placed in randomly selected microhabitats representative of each species and recorded temperature every 5 minutes throughout the sampling period at each study site. Dates of sampling are shown in Supplementary Table S1, which correspond to dry conditions at each study site. Five models were positioned on the ground in shaded refuge sites, while the remaining models were placed in open areas exposed to direct sunlight.

Additionally, air temperature and relative humidity data were recorded every 5 minutes using a HOBO micro–Station Data Logger IC-H21- USB (Onset Computer Corporation) for at least a one-year period at each study site.

2.4 Data analysis

2.4.1 Climate data

Air temperature data recorded from the weather stations installed at each study site for at least a one-year period (Supplementary Table S3) was summarised by computing the mean and 95% CI in one-hour time blocks across a 24-hour time interval.

2.4.2 Thermophysiological traits

The analysis of variation in Tpref, CTmin, and CTmax involved two main steps: (i) testing for sex differences within each population to obtain outcomes comparable with other studies, and (ii) evaluating the effects of snout-vent length (SVL), sex, and ecosystem type to explore the influence of these factors on the variation of thermal traits. All statistical analyses were performed in R (v. 4.4.0, R Core Team, 2024).

Before testing for sex differences within populations, the Levene and Shapiro-Wilk’s tests were used to assess for homogeneity of variances and normality of each thermophysiological trait respectively. If the data met the assumptions of normality and homogeneity, independent t-tests were performed to examine sex-based differences in the variables of interest. The non-parametric Kruskal-Wallis test was employed for data that violated these assumptions.

Linear models were built using the lm function from the STATS package (R Core Team, 2024), with each thermal trait as the response variable, and SVL, sex, and ecosystem as fixed factors. Ecosystem classification was based on the vegetation structure and composition in each lizard population and included three categories: paramo, evergreen, and inter-Andean. Pairwise post-hoc comparisons between ecosystems were performed using estimated margin means at 95% confidence level, with a p-value adjustment following the Tukey method (Lenth, 2019).

2.4.3 Assessment of vulnerability to changes in temperature

The thermal vulnerability of tropical Andean Stenocercus populations was assessed using three complementary approaches: (1) a graphical and descriptive analysis of lizards’ thermophysiological traits in relation to the maximum and minimum micro-environmental temperatures available in their habitat, along with the calculation of two thermal vulnerability metrics – (2) warming tolerance, and (3) thermal safety margins. The first approach was chosen to contextualise the thermal environments these lizards experience and, when combined with quantitative vulnerability assessments, provide a more comprehensive evaluation of how temperature variation may affect their survival from both micro-environmental and thermophysiological perspectives.

First, we explored graphically the relationship between thermal physiological traits of lizards and the temperature present in their microhabitats (Guerra-Correa et al., 2020). For each population, the temperature of OTMs placed in sun-exposed and shaded areas were averaged within hourly blocks and plotted along with the average critical thermal limits (CTmax and CTmin) and Tpref. In addition, the body temperatures of captured lizards at the corresponding hour of capture were included as a proxy of lizard activity across temperature ranges. Mean and ranges of Tb and Tsub values were calculated for each population, providing further insight into the temperature ranges of their activity.

Next, we examined the warming tolerance and thermal safety margin metrics to further evaluate vulnerability to temperature changes. Warming tolerance (WT) was calculated to estimate the extent of environmental warming that Stenocercus lizards can tolerate before their performance declines to lethal levels (Deutsch et al., 2008). Species with small WT values have limited physiological tolerances to temperature increases, whereas species with large WT values can tolerate warmer condition before their physiological performance declines to critical or fatal levels (Deutsch et al., 2008). In this context, the average CTmax of each population was subtracted from the 95th percentile of the maximum annual air temperature recorded at each site with micro weather stations (WT=CTmax-avg – Tair-P95) and projected under two warming scenarios: an increase of 1.5°C and 2°C (Hoegh-Guldberg et al., 2018). The 95th percentile was used to provide an accurate representation of the maximum air temperatures experienced by the lizards, while excluding recordings that otherwise may be atypical.

The thermal safety margin (TSM), on the other hand, was determined by calculating the difference between the maximum body temperature of active lizards and the 95th percentile of shaded microhabitat temperatures recorded by OTMs, as these values more accurately represent the thermal microenvironment available to lizards for avoiding overheating (Camacho et al., 2015) (TSM=Tb-max – Te-shade-P95). Small TSM values indicate that a species maintains an active body temperature close to the temperature available in its micro-environment to avoid overheating. This narrow margin suggests a reduced capacity to buffer against rising environmental temperatures, making the species potentially more vulnerable to climate warming. In contrast, a species with large TSM values inhabits micro-environments with a wider range of thermal conditions, allowing the organisms to effectively escape extreme heat exposure (Deutsch et al., 2008).

3 Results

3.1 Daily temperature variation

For the inter-Andean ecosystems, Pisquer exhibited more stable air temperatures conditions compared to Jerusalem RPPF, remaining ~10°C during the night and early morning, reaching a maximum of ~25°C around midday, and gradually decreasing to ~15°C by 5-6 PM (Figure 4A). At Jerusalem RPPF, early morning temperatures were colder than nighttime temperatures, reaching under 10°C, and midday temperatures peaked at 30°C and declining to ~20°C by late afternoon (Figure 4B). At Madrigal PR, air temperatures exhibited moderate fluctuations, remaining above 10°C during most of the night and early morning, peaking just over 20°C at midday, and remaining relatively stable throughout the afternoon (Figure 4C). In contrast, El Gullan SS showed greater temperature variability, with air temperatures dropping below 10°C at night and early morning, peaking above 30°C at midday, and decreasing to under 20°C by late afternoon (Figure 4D).

Air temperature across a 24-hour period averaged across a year for our seven tropical montane sites. **(A)** Pisquer, **(B)** Jerusalem RPPF, **(C)** Madrigal PR, **(D)** El Gullan SS, **(E)** El Angel ER, **(F)** Cotopaxi NP, **(G)** Chimborazo WPR.
Figure 4. Air temperature across a 24-hour period averaged across a year for our seven tropical montane sites. (A) Pisquer, (B) Jerusalem RPPF, (C) Madrigal PR, (D) El Gullan SS, (E) El Angel ER, (F) Cotopaxi NP, (G) Chimborazo WPR.

Paramo ecosystems showed the coldest air temperature conditions of all the ecosystem types. In El Angel ER and Chimborazo WPR, daily temperature patterns were similar, peaking at ~15°C around midday (Figures 4E, G). In Cotopaxi NP, however, air temperatures reached ~20°C at noon (Figure 4F). Night and early morning temperatures in Chimborazo WPR dropped to 0°C, while in El Angel ER and Cotopaxi NP, temperatures remained slightly above freezing.

3.2 Thermophysiological traits

A summary of thermophysiological trait measurements is provided in Table 2. Only one of the seven Stenocercus populations produced significant differences between males and females, with a different species exhibiting sex differences for each measure. Significant sex differences in Tpref were observed in S. guentheri from Jerusalem RPPF, with females exhibiting higher Tpref than males (Table 2a). In S. festae, sex differences were found in CTmin values, with males showing greater cold tolerance than females (Table 2b). Finally, S. ornatus yielded sex-specific differences for CTmax, with females being less tolerant of high temperatures than males (Table 2c).

Table 2. Average (Standard deviation) Tpref, CTmin, and CTmax values of Stenocercus species/populations assessed.

MeasureS. angelS. guentheri (Cotopaxi NP)S. cadleiS. festaeS. ornatusS. chotaS. guentheri (Jerusalem RPPF)
a. Tpref (°C)
N 124 (12)24 (12)26 (12)16 (8)26 (13)24 (12)24 (12)
All28.13 (1.52)27.70 (2.03)26.60 (3.50)25.77 (2.48)30.12 (1.89)29.77 (1.95)30.71 (2.05)
Males228.16 (1.61)27.31 (2.26)26.13 (4.45)25.57 (2.02)30.48 (1.79)30.38 (1.70)29.68 (1.67)
Females228.10 (1.50)28.09 (1.79)27.14 (1.97)25.97 (2.99)29.76 (2.00)29.15 (2.06)31.73 (1.92)
Sex difference 3t = -0.09t = 0.94t = 0.76t = 0.31t = 0.98t = -1.61t = 2.79
p = 0.93p = 0.36p = 0.46p = 0.76p = 0.34p = 0.12p = 0.01
b. CTmin (°C)
N 124(12)24(12)26(12)12 (7)26 (13)25 (12)24 (12)
All5.89 (0.83)7.05 (1.03)6.38 (0.94)6.80 (0.87)7.32 (0.61)7.14 (0.63)7.47 (0.61)
Males25.97 (0.68)6.82 (1.16)6.36 (0.88)6.12 (0.32)7.46 (0.71)7.06 (0.63)7.54 (0.64)
Females25.81 (0.99)7.19 (0.86)6.41 (1.05)7.28 (0.81)7.16 (0.45)7.22 (0.64)7.40 (0.60)
Sex difference 3t = -0.475t = 1.16chi-sq = 0.003t = 3.422t = -1.32chi-sq = 0.758t = -0.57
p = 0.64p = 0.26p = 0.96p = 0.009p = 0.20p = 0.38p = 0.571
c. CTmax (°C)
N 124 (12)24 (12)26 (12)16 (8)27 (13)25 (12)24 (12)
All39.45 (1.34)39.93 (2.07)38.74 (2.33)38.94 (1.31)39.33 (1.52)41.61 (1.62)39.94 (1.15)
Males239.53 (1.40)40.71 (1.92)38.88 (2.73)38.71 (1.62)39.92 (1.16)41.80 (1.60)39.80 (0.92)
Females239.37 (1.32)39.16 (1.99)38.58 (1.86)39.16 (0.96)38.70 (1.65)41.40 (1.69)40.08 (1.38)
Sex difference 3t = -0.30t = -1.95t = -0.33t = 0.68t = -2.20t = -0.62t = 0.57
p = 0.76p = 0.06p = 0.74p = 0.51p = 0.04p = 0.543p = 0.57

1Number of lizards with number of females in parentheses. 2Values shown for each sex when sex differences reported. 3T-test or Kruskal Wallis test (see methods). The sample size for S.festae was smaller than that of the other populations due to unforeseen circumstances encountered during sampling that forced us to stop fieldwork. Significant differences are in bold.

The linear model examining Tpref as a function of SVL, sex, and ecosystem was highly significant (F = 8.861, df=4,159, p = 0.001), explaining 16.2% of the variation in Tpref (Table 3a). The model indicated that neither SVL nor sex had a significant effect on Tpref. However, significant differences were observed between ecosystems (Figure 5A). Pairwise comparisons indicated that lizards inhabiting the evergreen ecosystems had significantly lower Tpref compared to those from inter-Andean ecosystems. No significant difference was found between evergreen and paramo ecosystems, but there was a marked difference between inter-Andean and paramo, where lizards from inter-Andean ecosystems had significantly higher Tpref.

Table 3. Linear model outcomes for three thermal traits (Tpref, CTmin, CTmax) with SVL, sex, and ecosystem as fixed variables.

Thermal traitRm2Rc> 2Estimate (°C)Std. Errort-valuep-value
a. Tpref0.180.160.001
SVL0.020.030.620.54
Sex-0.590.58-1.010.31
Evergreen – Inter-Andean-1.870.56-3.320.003
Evergreen – Paramo1.060.502.110.09
Inter-Andean – Paramo2.930.545.47<0.0001
b. CTmin0.190.170.001
SVL-0.020.01-1.430.15
Sex0.130.200.650.52
Evergreen – Inter-Andean-0.050.19-0.250.97
Evergreen – Paramo0.680.173.920.0004
Inter-Andean – Paramo0.730.184.020.0003
c. CTmax0.150.130.003
SVL0.0040.0230.190.85
Sex0.410.3961.040.30
Evergreen – Inter-Andean-1.630.38-4.240.0001
Evergreen – Paramo-0.160.34-0.470.89
Inter-Andean – Paramo1.470.373.990.0003

Significant differences are in bold.

Pairwise comparisons between ecosystem types for each thermophysiological trait evaluated. **(A)** Preferred body temperature (*T*<sub>pref</sub>), **(B)** critical thermal minimum (CT<sub>min</sub>), **(C)** critical thermal maximum (CT<sub>max</sub>). Ev, Evergreen; IA, Inter-Andean; Pa, Paramo. a- no significant differences, b - significant differences.
Figure 5. Pairwise comparisons between ecosystem types for each thermophysiological trait evaluated. (A) Preferred body temperature (Tpref), (B) critical thermal minimum (CTmin), (C) critical thermal maximum (CTmax). Ev, Evergreen; IA, Inter-Andean; Pa, Paramo. a- no significant differences, b - significant differences.

The linear model for CTmin, was also significant (F = 9.228, df=4,156, p = 0.001), explaining 17.1% of the variance (Table 3b). As above, neither SVL nor sex significantly affected CTmin of Stenocercus lizards, but significant variation was found among ecosystems (Figure 5B). Pairwise comparisons between ecosystem categories revealed that CTmin of lizards from the evergreen and inter-Andean ecosystems was not significantly different. However, paramo lizards had significantly lower CTmin than those from the evergreen and inter-Andean ecosystems.

As with the other two measures, the linear model for CTmax was significant (F = 7.035, df=4,161, p = 0.03), explaining 12.8% of the variance, with only ecosystems significantly impacting CTmax (Table 3c). Pairwise comparisons showed no significant difference between lizards from evergreen and paramo ecosystems. In contrast, lizards from inter-Andean ecosystems had significantly higher CTmax than to those from the other two ecosystems (Figure 5C).

Despite the statistical differences observed between sexes within some populations, the linear models did not show a significant effect of sex on Tpref, CTmin, or CTmax. Therefore, the average values of each thermophysiological traits were used for downstream analysis (Table 2).

3.3 Thermal vulnerability

3.3.1 Thermophysiological traits in relation to micro-environmental temperatures

Average and ranges of Tb, Tair, and Tsub for each population are summarised in Table 4. Graphical depiction of the relationship between thermal physiological traits and environmental temperatures are presented in Figure 6, separately for each species/population and organised by ecosystem type: inter-Andean (Figures 6A, B), evergreen (Figures 6C, D) and paramo (Figures 6E–G).

Table 4. Average and range Tb, Tsub, and Tair recorded for Stenocercus species/populations from high-altitude tropical montane ecosystems.

Species/PopulationsTb (°C)Tsub (°C)Tair (°C)
a. S. guentheri (Jerusalem RPPF) (N = 24)29.7(20.5 – 35.1)29.11(20.8 – 38.4)27.74(20.7 – 31.6)
b. S. chota(N = 24)28.45(21.7 – 34.8)26.52(18.2 – 43.5)24.29(18.9 – 30.3)
c. S. ornatus(N = 26)27.51(18.5 – 34.9)24.56(18.9 – 31.2)25.38(19.4 – 29.9)
d. S. festae(N = 16)26.94(18.2 – 34.8)25(16.8 – 46.5)22.71(15.7 – 27)
e. S. angel(N = 24)26.75(20.1 – 32.3)25.38(13.5 – 38.2)17.39(12.5 – 21.7)
f. S. guentheri (Cotopaxi)(N = 24)25.79(16.5 – 31.8)23.86(14.4 – 32.4)19.14(15.2 – 22.5)
g. S. cadlei(N = 24)22.81(10.3 – 33.7)23.01(10.8 – 49.3)15.45(7.4 – 21.3)
Relationship between thermal physiological traits and operative temperature for each assessed population. The red curves represent the hourly average of OTMs placed in sun-exposed microhabitats, while blue curves show the hourly average of OTMs in shaded microhabitats. Black dots represent the body temperature of active individuals plotted against the corresponding hour of capture. The dashed lines show the average *T*<sub>pref</sub>, CT<sub>min</sub>, and CT<sub>max</sub> for each population. **(A)***S. guentheri* from Jerusalem RPPF, **(B)***S. chota* from Pisquer, **(C)***S. ornatus* from Madrigal PR, **(D)***S. festae* from El Gullan SS, **(E)***S. angel* from El Angel ER, **(F)***S. guentheri* Cotopaxi NP, **(G)***S. cadlei* from Chimborazo WPR.
Figure 6. Relationship between thermal physiological traits and operative temperature for each assessed population. The red curves represent the hourly average of OTMs placed in sun-exposed microhabitats, while blue curves show the hourly average of OTMs in shaded microhabitats. Black dots represent the body temperature of active individuals plotted against the corresponding hour of capture. The dashed lines show the average Tpref, CTmin, and CTmax for each population. (A)S. guentheri from Jerusalem RPPF, (B)S. chota from Pisquer, (C)S. ornatus from Madrigal PR, (D)S. festae from El Gullan SS, (E)S. angel from El Angel ER, (F)S. guentheri Cotopaxi NP, (G)S. cadlei from Chimborazo WPR.

Inter-Andean sites revealed similar patterns. At Jerusalem RPPF, and between 0900 and 1500 hours, sun exposed microhabitats reached temperatures exceeding the average CTmax of S. guentheri (Figure 6A). Moreover, around midday, shaded areas warmed to values close to the population’s average Tpref, which also aligned closely with the average Tb (Table 4a). In contrast, early morning temperatures were below the average CTmin (Figure 6A). At Pisquer, midday temperatures in sun-exposed microhabitats peaked above the average CTmax of S. chota, while shaded areas approached the average Tpref (Figure 6B). Tb of this population ranged between 21.7°C and 34.8°C (Table 4b), with an average lower than the species’ average Tpref. Additionally, shaded microhabitats also remained above the average CTmin (Figure 6B).

Evergreen sites showed broadly similar patterns, but with some key differences between them. Between 1000 and 1200 hours at El Madrigal PR, sun-exposed microhabitats exceeded the average CTmax of S. ornatus (Figure 6C). During the same period, shaded areas were about 10°C cooler than the average Tpref. This thermal contrast enabled lizards to maintain Tb values between 18.5°C and 34.9°C (Table 4c). The average CTmin was also lower than the minimum recorded micro-environmental temperature. At El Gullan SS, sun-exposed areas reached peak temperatures before midday, matching the average CTmax of S. festae (Figure 6D). In early morning, the coolest shaded temperatures were near the average CTmin. Lizards here exhibited Tb values ranging from 18.2°C to 34.8°C (Table 4d), with a mean close to their average Tpref.

Nighttime temperatures were a challenge in paramos ecosystems. At El Angel ER, sun-exposed microhabitats peaked at 1200 hours, reaching temperatures close to the population’s average Tpref and approximately 10°C below the average CTmax of S. angel (Figure 6E). Shaded areas were often cooler than the average CTmin, especially at night. Despite this, average Tb remained above 26°C (Table 4e). At Cotopaxi NP, maximum temperatures in sun-exposed areas never reached the average CTmax of S. guentheri (Figure 6F). From 1800 to 0800 hours, microhabitat temperatures fell below the average CTmin. Lizards showed Tb values ranging from 16.5°C to 31.8°C (Table 4f), reflecting the highly variable thermal environment. Finally, at Chimborazo WPR, sun-exposed microhabitats reached the average CTmax of S. cadlei around midday (Figure 6G). At night, temperatures dropped below the average CTmin. The consistently cold conditions resulted in Tb values ranging from 10.3°C to 33.7°C, with an average lower than the species’ Tpref (Table 4g).

3.3.2 Thermal safety margins and warming tolerance

Thermal safety margins (TSM) and warming tolerance (WT) under three scenarios (present, +1.5°C, and +2°C) for each species/population are presented in Table 5.

Table 5. Thermal safety margins (TSM) and warming tolerance (WT) under three scenarios for Stenocercus species/populations assessed.

Species/populationsTSM (°C)WT (present)WT (+1.5 °C)WT (+2°C)
a. S. guentheri (Jerusalem RPPF)-1.435.634.133.63
b. S. chota0.7315.6914.1913.69
c. S. ornatus6.7312.7811.2810.78
d. S. festae8.67-3.68-5.18-5.68
e. S. angel17.7522.7521.2520.75
f. S. guentheri (Cotopaxi)18.317.0215.5215.02
g. S. cadlei22.0920.51918.5

Species inhabiting inter-Andean ecosystems appear to be the most vulnerable to rising temperatures in their habitats. The negative TSM values and small WT scores of S. guentheri from Jerusalem RPPF place this population at the highest risk among all focal populations. Meanwhile, S. chota is close to the limit of its physiological capacity to buffer high temperatures in its microhabitats but can still tolerate current and projected warming scenarios.

Lizards from evergreen ecosystems show that their microhabitats remain more than 6°C below the point at which activity becomes restricted. However, the negative WT values of S. festae indicate that these lizards may still be at risk. A completely different pattern emerges for species inhabiting paramo ecosystems. The three populations evaluated in this ecosystem type (S. angel from El Angel ER, S. guentheri from Cotopaxi NP, and S. cadlei from Chimborazo WPR) show positive TSM and WT values, implying sufficient physiological resilience to avoid overheating.

4 Discussion

Across the studied tropical Andean ecosystems, pronounced differences in daily temperature variability and microhabitat thermal conditions were closely associated with variation in lizard thermal preferences, tolerances, and vulnerability, supporting our hypothesis that local climate and vegetation interactions shape thermophysiological traits of high-altitude Stenocercus populations. For instance, lizards inhabiting ecosystems characterised by high diurnal temperature conditions, such as Inter-Andean ecosystems, exhibit the highest CTmax and Tpref values. In contrast, paramo lizards show the lowest CTmin values due to the cold conditions they are exposed in their microenvironments. Furthermore, microhabitat analyses revealed that structurally complex vegetation in tropical montane ecosystems created diverse thermal mosaics, allowing lizards to behaviourally thermoregulate by exploiting sun-exposed or shaded areas. Despite this buffering capacity, thermal safety margins and warming tolerance varied markedly among populations. Inter-Andean populations were the most vulnerable to warming due to frequent exposure to temperatures near or above their critical thermal maximum, whereas paramo populations maintained positive safety margins and warming tolerance, indicating greater resilience to overheating. Overall, these results demonstrate that daily temperature variability and vegetation-driven microclimatic heterogeneity jointly influence thermal flexibility and vulnerability in high-altitude tropical montane lizards.

Various physical mechanisms in the Tropical Andes, such as the El Niño-Southern Oscillation and the presence of trade winds to the north, drive temporal variability that shapes the region’s climate (Martínez et al., 2011; Young et al., 2007). This climatic variability, combined with the complex topography of the Andes, has created a diverse array of climatic niches, promoting physiological specialisation in response to differing thermal and rainfall regimes (Salazar et al., 2024; Sheldon, 2019). For example, macroclimate conditions in high-altitude tropical Andean ecosystems show marked daily temperature fluctuations (Figure 4), which we propose directly influence the thermal exposure of Stenocercus lizards at the microhabitat scale. Additionally, the uplift of the Andes led to the formation of isolated land areas, each hosting distinct ecosystems with representative vegetation assemblages.

One such ecosystem is the inter-Andean valleys, where precipitation is limited due to the rain shadow effect caused by the surrounding high cordilleras (Neill, 1999). These arid valleys are dominated by xerophytic plant species from the families Cactaceae and Agavaceae, along with small shrubs and trees from the Euphorbiaceae and Fabaceae families (Neill, 1999; Werner, 2009). This distinctive vegetation composition results in open microhabitats with reduce shaded areas, thereby exposing lizards to intense solar radiation and elevated temperatures, especially during midday hours. Consequently, S. guentheri and S. chota populations inhabiting inter-Andean ecosystems exhibit higher Tpref and CTmax values compared to those living in evergreen and paramo ecosystems.

In contrast, evergreen ecosystems, now reduced to highly localised and increasingly fragmented remnants, are under severe threat from burning, grazing, and the relentless expansion of the agricultural frontier (Ministerio del Ambiente del Ecuador, 2013). Despite their vulnerability, these ecosystems provide a markedly different thermal environment for lizards. Characterised by a low and open canopy, evergreen ecosystems support a rich assemblage of epiphytes, particularly from the Orchidaceae and Bromeliaceae families (Ministerio del Ambiente del Ecuador, 2013). This complex vertical structure contributes to a cooler and more thermally buffered microclimate, offering lizards access to shaded refuges and reduced exposure to extreme heat. As a result, lizard populations in these ecosystems (S. ornatus and S. festae) tended to exhibit lower thermal preferences and heat tolerances than those in the more exposed inter-Andean valleys.

Finally, paramo ecosystems, situated at even higher elevations, present a unique suite of environmental conditions. These ecosystems are shaped by intense daily temperature fluctuations, strong winds, high ultraviolet radiation, frequent precipitation, and low atmospheric pressure (Ruiz et al., 2011; Young et al., 2011; Cuesta et al., 2012; CEPF, 2021). The vegetation in these landscapes consists of dense shrub-herbaceous assemblages dominated by sclerophyllous shrubs such as Chuquiraga and Diplostephium, cushion-forming plants like Xenophyllum and Azorella, and low-growing grasses of the genus Calamagrostis (Cuesta et al., 2012; Romoleroux et al., 2023). These plant forms create microhabitats that are both thermally challenging and spatially heterogeneous. Lizards inhabiting paramo ecosystems (S. guentheri, S. angel, and S. cadlei) are therefore adapted to withstand cold temperatures and tend to prefer lower body temperatures than their counterparts in drier, sun-exposed inter-Andean environments. Additionally, the unique structural and climatic features of paramo ecosystems contribute to shaping distinct physiological tolerances, highlighting the critical role of habitat-specific environmental pressures in driving thermal adaptation in high-altitude tropical Andean Stenocercus lizards.

According to the thermal adaptation hypothesis, the minimum and maximum temperatures of an organism’s microenvironment should align with its thermal limits, thereby minimising the physiological costs associated with maintaining thermal tolerances (Angilleta, 2009; Janzen, 1967; Kaspari et al., 2015). This framework may help explain the observed variation in thermophysiological traits among high-altitude tropical montane Stenocercus populations, which differ according to the ecosystem types they inhabit. However, considering the relatively recent diversification of this lizard group in the northern Andes (Torres-Carvajal, 2007b), further research is needed to determine whether their physiological traits result from short-term phenotypic plasticity, longer-term thermal acclimation, or genetic adaptation, as documented in other taxa (Bujan et al., 2020; Martin et al., 2019; Sørensen et al., 2016). The isolated land formations created by the uplift of the Andes may have further promoted the divergence of thermophysiological traits within this lizard clade by facilitating climate niche specialisation at the microhabitat scale (Dangles, 2023; Flantua and Hooghiemstra, 2018; Hazzi et al., 2018). Yet, this degree of specialisation may come at a cost, increasing these lizards’ vulnerability to ongoing climate warming. The extent to which Stenocercus lizards can buffer against this threat likely depends on the availability of suitable microhabitats that reduce overheating risk, as well as behavioural strategies that allow them to effectively regulate their body temperature.

Daylight ambient temperatures in tropical montane microhabitats begin to rise around 0800 hours and decreased by 1700 hours, defining the activity period of Stenocercus lizards. However, microenvironmental temperature conditions within and beyond this activity window vary across tropical Andean ecosystems, exposing each lizard population to differing levels of vulnerability (Pincebourde and Suppo, 2016). Simple vulnerability indices, such as thermal safety margins (TSM) and warming tolerance (WT), are widely used to evaluate species vulnerability to rising temperatures (Deutsch et al., 2008). These indices quantify how close a species’ thermal limits and optimal body temperatures are to projected warming scenarios, offering insights into their capacity to cope with rising temperatures (Clusella-Trullas et al., 2021). This framework is based on the premise that temperature sensitivity of physiological performance plays a critical role in determining species distributions and survival (Sunday et al., 2012). Consequently, these indices serve as valuable tools for comparing vulnerability across different species or populations.

Although S. chota and S. guentheri inhabit inter-Andean ecosystems, their microhabitats presented contrasting thermal characteristics, leading to opposing thermal vulnerability outcomes. The S. guentheri population from Jerusalem RPPF experienced the most severe thermal stress of all evaluated populations. On the one hand, they suffered from cold physiological stress during some hours of nighttime, as their CTmin is higher than the lowest temperatures available in their microhabitats. On the other hand, daytime temperatures in their microhabitats exceeded their average CTmax, being greater at midday when temperatures are more than 10°C higher compared to the average CTmax. As a result, they exhibited negative thermal safety margins and minimal warming tolerance, which may increase mortality rates and decrease population growth (Kearney, 2013; Munch and Salinas, 2009). Conversely, S. chota showed no evidence of thermal stress from either cold or heat based on the thermal conditions in their microhabitats. However, their narrow thermal safety margin indicates that they inhabit environments near their physiological optimum (Deutsch et al., 2008). Therefore, warming is likely to cause these lizards to retreat to cool refuges limiting their activity and constraining other functions such as foraging and reproduction (Sinervo et al., 2010).

Lizard species inhabiting evergreen ecosystems, such as S. festae and S. ornatus, exhibited average CTmin values below the minimum temperatures of their microhabitats. However, midday temperatures in their micro-environments approached or exceeded their average CTmax. Despite this, these populations maintained favourable thermal safety margins, suggesting positive physiological responses to cope with high temperatures in their microhabitats. Interestingly, S. festae exhibited negative warming tolerance under current temperature conditions and across the two projected warming scenarios, suggesting an inability to tolerate even slightly higher temperatures than those currently experienced (Anderson et al., 2022). Conversely, S. ornatus showed no physiological limitations under any of the three assessed warming scenarios, indicating a greater capacity to cope with rising temperatures. Although evergreen ecosystems typically offer suitable thermal microhabitats that lizards to avoid overheating, ongoing habitat fragmentation is diminishing these refuges and increasing exposure to high temperatures. This phenomenon is evident at El Gullan SS, where large portions of the surrounding landscape have been converted into pine plantations, grazing areas, and agricultural lands. Such extensive alteration is suggested to intensify thermal stress for S. festae populations. Therefore, urgent action is needed to halt the continued degradation of these ecosystems and to preserve the thermal habitats essential for the survival of this species.

Stenocercus species from paramo ecosystems, including S. angel, S. guentheri, and S. cadlei, inhabit the coldest environments among all analysed populations. The extremely low nighttime temperature in their microhabitats fall below their average CTmin for substantial periods, increasing their dependence on thermal refuges to avoid extreme cold and enhancing their cold tolerance (Pintanel et al., 2019; Salazar et al., 2024). In contrast, the maximum temperatures in their microhabitats remained below their average CTmax, suggesting they are unlikely to experience physiological stress from heat exposure. Additionally, thermal safety margins indicate that these lizards possess sufficient physiological resilience to avoid overheating. This is further supported by warming tolerance calculations, showing that even under the highest projected warming scenario of +2°C, paramo lizards will not be physiologically constrained. These findings align with other studies, which suggest that lizards inhabiting thermally variable environments exhibit greater physiological tolerance to warming, making them less vulnerable to rising temperatures compared to populations in more thermally stable conditions (Lara-Resendiz et al., 2019; Yuan et al., 2018).

In the context of climate change, terrestrial ectotherms must rapidly respond to novel thermal environments without prolonged exposure to suboptimal temperatures that could impair their performance. By either adapting physiologically, adjusting their behaviour or employing both strategies, organisms can mitigate potential impacts of climate change on their populations (Angilletta et al., 2002; Muñoz et al., 2014). Behavioural thermoregulation is an effective short-term strategy to minimise exposure to extreme climate conditions (Angilletta et al., 2002). Additionally, studies on tropical anole species suggest that behavioural thermoregulation can shield organisms from selective pressures on upper physiological thermal limits, while cold tolerance remains under stronger selection (Muñoz et al., 2014). Thus, examining how organisms interact with the available microthermal habitats can help elucidate patterns of physiological divergence in tropical montane species as well as support predictions of vulnerability to climate change (Angilleta, 2009; Huey et al., 2003).

In conclusion, the microscale environmental conditions experienced by high-altitude tropical Andean Stenocercus populations have shaped specialised thermophysiological profiles tailored to the thermal variability in their habitats. However, thermophysiological responses vary among populations depending on their exposure to environmental changes. Particular attention should be given to populations such as S. guentheri (inter-Andean) and S. festae, which face challenges due to either reduced performance under high temperature conditions in their habitats or limited physiological tolerances to warming. For these populations, thermoregulatory behaviours may be the primary mechanism to cope with rising temperatures, given the constraints ectotherm tropical Andean species face in shifting their elevational ranges (Forero-Medina et al., 2010). Long-term monitoring of these populations is important for understanding their adaptative strategies in behaviour and physiology, as well as the implications for their ecological niches. Moreover, such monitoring could inform conservation policies that advocate for the protection of high-elevation climate refugia. While it is evident that global warming poses significant risks to populations like S. festae and S. guentheri, other Stenocercus populations, such as those inhabiting paramo ecosystems may not be as adversely affected by rising temperatures as reported for other cold-adapted lizard species (Doan et al., 2022). However, further research into the mechanisms of cold tolerance in these lizards is essential to better understand how these traits might evolve or constraint adaptation to warming scenarios. Finally, exploring the adaptive significance of thermal developmental phenotypic plasticity (an area currently unexplored in Stenocercus lizards) could enhance predictions of vulnerability in the face of climate change. This mechanism, which has been suggested to have organisational effects that potentially constrain phenotypic development later in life (While et al., 2018), may hold key insights into the resilience of tropical Andean species in a warming world.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/famrs.2026.1758509/full#supplementary-material

Supplementary material Supplementary material at the source

Supplementary material Supplementary material at the source

Footnotes

Edited by: Luisa Maria Diele Viegas, Federal University of Bahia (UFBA), Brazil

Reviewed by: Zhensheng Liu, Northeast Forestry University, China

Hugo Andrade, Federal University of Sergipe, Brazil

Statements

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

The author(s) declared that financial support was received for this work and/or its publication. This work received financial support from two funding sources: internal funds provided by the School of Agriculture, Biomedicine & Environment, of La Trobe University, Melbourne, Australia, and the Australian Research Council Discovery Project (grant number: DP170102370).

Data availability

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics approval

The animal study was approved by La Trobe University Animal Ethics Committee. Project No.: AEC-21-028. Fieldwork permits were issued by the Ministry of Environment, Water, and Ecological Transition (MAAE-ARSFC-2021-1463, MAATE-ARSFC-2022-2330, MAATE-ARSFC-2023-3250, MAAE-DBI-CM-2022-0229). The study was conducted in accordance with the local legislation and institutional requirements.

Author contributions

EG-C: Formal analysis, Project administration, Data curation, Investigation, Writing – review & editing, Methodology, Conceptualization, Writing – original draft. JG: Writing – review & editing, Supervision, Resources. RP: Resources, Funding acquisition, Formal analysis, Writing – review & editing, Methodology, Supervision.

Acknowledgements

Thanks to all fieldwork assistants for their dedication and hard work: Sebastián Mena, Marek Castel, Salomé Pillajo, Erick Troncoso, Sofía González, Malki Bustos, Jefferson Mora, Michelle Estévez, and Kerly Trávez. To the park rangers for welcoming us with respect and generously shared their facilities: Óscar Muñoz, Edwin Taipe, Eduardo Quinga, Giovanni Tocto, and Miguel Paguay. To the National Parks authorities: Damián Ponce, Mario Jarrín, and Paúl Tito, as well as the community members of Pulinguí San Pablo and Patricia Vizuete, for granting us the space and authorisation to conduct this research. To Andrés Mármol and Esteban Ponguillo, for dedicating time to build the 3D models as well as to Omar Torres-Carvajal and Andrés Merino Viteri for granting access to preserve specimens and providing necessary workspace. Special thanks to Lily Leahy and Vanessa Kellermann for their guidance and expertise on data analysis. We are also grateful to Maria Thaker and Geoff While for their comments on an early version of this manuscript.

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Citation

Guerra-Correa, E. S., et al. (2026). Ecophysiology and vulnerability to warming of Whorl-tail Iguanas (Tropidurinae: Stenocercus) from the Tropical Andes of Ecuador. Frontiers in Amphibian and Reptile Science, Volume 4. https://doi.org/
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Copyright © 2026 Guerra-Correa, Guayasamin and Peters.

License: https://creativecommons.org/licenses/by/4.0/

*Correspondence: Estefany S. Guerra-Correa

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