Towards a mechanistic understanding of the responses of large terrestrial mammals to heat and aridity associated with climate change

Revisiting concepts of thermal physiology: understanding negative feedback and set-point in mammals, birds, and lizards

The thermoregulatory system of homeothermic endotherms operates to attain thermal equilibrium, that is no net loss or gain of heat, where possible, under a thermal challenge, and not to attain a set-point or any other target body temperature. The concept of a set-point in homeothermic temperature regulation has been widely misinterpreted, resulting in such confusion that some thermoregulation specialists have recommended that it be abandoned. But the set-point concept has enjoyed a resurgence in a different domain, lizard microclimate selection. We review the principles of thermoregulation in homeotherms, endorse a negative feedback system with independent set-points for individual thermo-effectors as its core mechanism, and address the misconceptions about homeothermic set-point. We also explore the concept of set-point range in lizard microclimate selection and conclude that there is substantial convergence between that concept and the set-points of homeothermic thermo-effectors, as thresholds. In neither homeothermic nor lizard thermoregulation is the concept of a unitary set-point appropriate. We review the problems of measuring the set-points for lizard microclimate selection. We do not believe that the set-point concept in thermoregulation should be abandoned just because it has been misinterpreted by some users. It is a valid concept, identifying the threshold body temperatures at which regulatory thermo-effectors will be activated, to aid in attaining thermal equilibrium.

Comparative physiological and biochemical assessment of the heat tolerance of dwarf Vechur, Kasaragod, and standard-size crossbred cattle under humid, hot conditions

Reduced body size is an ecological response to climate change. Differential responses to heat stress in phenotypically diverse bovine lineages may imply a body size-dependent stress response. Heat-tolerant dwarf Vechur, Kasaragod (Bos taurus indicus), and heat-sensitive crossbred (CB, B. t. indicus x B. t. taurus) cattle were tested physiologically, biochemically, and in terms of cellular protein expression. Thirty adult lactating cows (ten Vechur, Kasaragod, and CBs each) were allowed to graze during the summer. The environmental parameters measured included Ta (ambient temperature), RH (humidity), WS (wind speed), and SR (solar radiation intensity). In addition, the temperature humidity index (THI), heat load index (HLI), and accumulated heat load (AHL) were computed. The panting score (PS) was determined using breath characteristics. Numerous physiological (rectal temperature-RT, respiratory rate-RR and pulse rate-PR), haematological, and biochemical (serum cortisol) heat stress markers were identified and validated. RT, RR and PR were evaluated to determine the linear correlation coefficients and predictors. The correlation coefficients in CB were significantly higher than in Vechur and Kasaragod (p < 0.01). Stepwise regressions showed that in CB, Ta alone was the environmental measure that best described the indicator variables PS, the difference between RT recorded at half-hour intervals (RTdiff, R2 = 0.925), and white blood cell count (R2 = 0.984). Differences in cellular protein expression were also evident. Under heat stress conditions, linear discriminants based on RT, RR, and PR separated dwarf (Vechur and Kasaragod) and crossbred cattle into various clusters, and significant breed-wise grouping was identified based on haematological parameters in pre-stress and heat stress. The study established the variable heat stress response of phenotypically divergent Bos lineages and relevant heat stress markers and thermal indices for measuring heat stress.

Solar radiation alters heat balance and thermoregulation in a flying desert bee

Solar radiation is an important environmental variable for terrestrial animals, but its impact on the heat balance of large flying insects has been poorly studied. Desert bees are critical to ecosystem function through their pollination services, and are exposed to high radiant loads. We assessed the role of solar radiation in the heat balance of flying desert Centris pallida bees by calculating heat budgets for individuals in a respirometer in shaded versus sunny conditions from 16 to 37°C air temperatures, comparing the large and small male morphs and females. Solar radiation was responsible for 43 to 54% of mean total heat gain. Bees flying in the sun had thorax temperatures 1.7°C warmer than bees flying in the shade, storing a very small fraction of incident radiation in body tissues. In most cases, flight metabolic rate was not suppressed for bees flying in the sun, but evaporative water loss rates more than doubled. The most dramatic response to solar radiation was an increase in convection, mediated by a more than doubling of convective conductance, allowing thermoregulation while conserving body water. In large morph males and females, the increased convective conductance in the sun was mediated by increased heat transfer from the thorax to abdomen. Because convection is limited as body temperatures approach air temperatures, solar radiation combined with warming air temperatures may cause endothermic flying bees to reach a tipping point at which increases in non-sustainable evaporation are necessary for survival.

Proposing a strategy based on body-thermal status to improve the welfare of heat-stressed and water-deprived goats (Capra hircus)

OBJECTIVE

Despite the considerable body of research on the effects of heat stress coupled with water scarcity (either through restriction or deprivation) on goats, aimed at enhancing their welfare, there remains a notable gap in the literature regarding the subsequent period following water restoration, during which the cumulative impact is fully alleviated. In response to this gap, we propose a strategy grounded in the assessment of body-thermal status to improve the welfare of heat-stressed and water-deprived goats. Specifically, our strategy seeks to determine the minimally required recovery interval necessary to completely mitigate the residual effects of water deprivation endured for a duration of 72 hours.

METHODS

Eight healthy Aardi bucks, aged 10 months and weighing 30 kg, were subjected to three distinct stages: euhydration, dehydration, and rehydration. Each stage spanned for 72 hours except for the rehydration stage, which was left unrestricted. Various meteorological, biophysiological, and thermophysiological measurements were subsequently recorded.

RESULTS

Exposure of heat-stressed goats, as indicated by the temperature-humidity index values, to a 72 hours deprivation period resulted in noticeable (p<0.05) alterations in their biophysiological (daily feed intake, body weight, and feces water content) and thermophysiological responses (core, rectal, skin, and surface temperatures, respiratory and heart rates, internal, external, and total body-thermal gradients, heat tolerance and adaptability coefficients, heterothermial total body-heat storage, and total water conservation). Remarkably, our findings demonstrate that all assessed variables, whether measured or estimated, returned to their baseline euhydration levels within 10 days of commencing the rehydration phase.

CONCLUSION

In order to improve the welfare of heat-stressed and 72 hours water-deprived goats, it is imperative to allow a recovery period of no less than 10 days following the restoration of water access prior to initiating any subsequent experiments involving these animals. Such experiments, addressing these critical aspects, serve to advance our understanding of goat welfare and obviously hold promise for contributing to future food security and economic viability.

Impacts of climate change and human activities on three Glires pests of the Qinghai-Tibet Plateau

BACKGROUND

The range of Glires is influenced by human activities and climate change. However, the extent to which human activities and environmental changes have contributed to this relationship remains unclear. We examined alterations in the distribution changes and driving factors of the Himalayan marmot, plateau pika, and plateau zokor on the Qinghai-Tibet Plateau (QTP) using the maximum entropy (MaxEnt) model and a geographical detector (Geodetector).

RESULTS

The MaxEnt model showed that the contribution rates of the human footprint index (HFI) to the distribution patterns of the three types of Glires were 46.70%, 58.70%, and 59.50%, respectively. The Geodetector results showed that the distribution pattern of the Himalayan marmot on the QTP was influenced by altitude and the normalized difference vegetation index (NDVI). The distribution patterns for plateau pikas and plateau zokors were driven by HFI and NDVI. Climate has played a substantial role in shaping suitable habitats for these three Glires on the QTP. Their suitable area is expected to decrease over the next 30-50 years, along with their niche breadth and overlap. Future suitable habitats for the three Glires tended to shift toward higher latitudes on the QTP.

CONCLUSION

These findings underscore the impacts of environmental and human factors on the distribution of the three Glires on the QTP. They have enhanced our understanding of the intricate relationships between Glires niches and environments. This can aid in identifying necessary interventions for developing effective early warning systems and prevention strategies to mitigate Glires infestations and plague epidemics on the QTP. © 2024 Society of Chemical Industry.

A role of epigenetic mechanisms in regulating female reproductive responses to temperature in a pest beetle

Many species are threatened by climate change and must rapidly respond to survive in changing environments. Epigenetic modifications, such as DNA methylation, can facilitate plastic responses by regulating gene expression in response to environmental cues. Understanding epigenetic responses is therefore essential for predicting species' ability to rapidly adapt in the context of global environmental change. Here, we investigated the functional significance of different methylation-associated cellular processes on temperature-dependent life history in seed beetles, Callosobruchus maculatus Fabricius 1775 (Coleoptera: Bruchidae). We assessed changes under thermal stress in (1) DNA methyltransferase (Dnmt1 and Dnmt2) expression levels, (2) genome-wide methylation and (3) reproductive performance, with (2) and (3) following treatment with 3-aminobenzamide (3AB) and zebularine (Zeb) over two generations. These drugs are well-documented to alter DNA methylation across the tree of life. We found that Dnmt1 and Dnmt2 were expressed throughout the body in males and females, but were highly expressed in females compared with males and exhibited temperature dependence. However, whole-genome methylation did not significantly vary with temperature, and only marginally or inconclusively with drug treatment. Both 3AB and Zeb led to profound temperature-dependent shifts in female reproductive life history trade-off allocation, often increasing fitness compared with control beetles. Mismatch between magnitude of treatment effects on DNA methylation versus life history effects suggest potential of 3AB and Zeb to alter reproductive trade-offs via changes in DNA repair and recycling processes, rather than or in addition to (subtle) changes in DNA methylation. Together, our results suggest that epigenetic mechanisms relating to Dnmt expression, DNA repair and recycling pathways, and possibly DNA methylation, are strongly implicated in modulating insect life history trade-offs in response to temperature change.

Sloth metabolism may make survival untenable under climate change scenarios

Although climate change is predicted to have a substantial effect on the energetic requirements of organisms, the longer-term implications are often unclear. Sloths are limited by the rate at which they can acquire energy and are unable to regulate core body temperature (Tb) to the extent seen in most mammals. Therefore, the metabolic impacts of climate change on sloths are expected to be profound. Here we use indirect calorimetry to measure the oxygen consumption (VO2) and Tb of highland and lowland two-fingered sloths (Choloepus hoffmanni) when exposed to a range of different ambient temperatures (Ta) (18 °C -34 °C), and additionally record changes in Tb and posture over several days in response to natural fluctuations in Ta. We use the resultant data to predict the impact of future climate change on the metabolic rate and Tb of the different sloth populations. The metabolic responses of sloths originating from the two sites differed at high Ta's, with lowland sloths invoking metabolic depression as temperatures rose above their apparent 'thermally-active zone' (TAZ), whereas highland sloths showed increased RMR. Based on climate change estimates for the year 2100, we predict that high-altitude sloths are likely to experience a substantial increase in metabolic rate which, due to their intrinsic energy processing limitations and restricted geographical plasticity, may make their survival untenable in a warming climate.

Can large-scale tree planting in China compensate for the loss of climate connectivity due to deforestation?

Extensive deforestation has been a major reason for the loss of forest connectivity, impeding species range shifts under current climate change. Over the past decades, the Chinese government launched a series of afforestation and reforestation projects to increase forest cover, yet whether the new forests can compensate for the loss of connectivity due to deforestation-and where future tree planting would be most effective-remains largely unknown. Here, we evaluate changes in climate connectivity across China's forests between 2015 and 2019. We find that China's large-scale tree planting alleviated the negative impacts of forest loss on climate connectivity, improving the extent and probability of climate connectivity by 0-0.2 °C and 0-0.03, respectively. The improvements were particularly obvious for species with short dispersal distances (i.e., 3 km and 10 km). Nevertheless, only ~55 % of the trees planted in this period could serve as stepping stones for species movement. This indicates that focusing solely on the quantitative target of forest coverage without considering the connectivity of forests may miss opportunities in tree planting to facilitate climate-induced range shifts. More attention should be paid to the spatial arrangement of tree plantations and their potential as stepping stones. We then identify priority areas for future tree planting to create effective stepping stones. Our study highlights the potential of large-scale tree planting to facilitate range shifts. Future tree-planting efforts should incorporate the need for species range shifts to achieve more biodiversity conservation benefits under climate change.

Weather influences survival probability in two coexisting mammals directly and indirectly via competitive asymmetry

Ecologists have studied the role of interspecific competition in structuring ecological communities for decades. Differential weather effects on animal competitors may be a particularly important factor contributing to the outcome of competitive interactions, though few studies have tested this hypothesis in free-ranging animals. Specifically, weather might influence competitive dynamics by altering competitor densities and/or per-capita competitive effects on demographic vital rates. We used a 9-year data set of marked individuals to test for direct and interactive effects of weather and competitor density on survival probability in two coexisting mammalian congeners: Columbian ground squirrels (Urocitellus columbianus) and northern Idaho ground squirrels (Urocitellus brunneus). Ambient temperature and precipitation influenced survival probability in both species, but the effects of weather differed between the two species. Moreover, density of the larger Columbian ground squirrel negatively impacted survival probability in the smaller northern Idaho ground squirrel (but not vice versa), and the strength of the negative effect was exacerbated by precipitation. That is, cooler, wetter conditions benefited the larger competitor to the detriment of the smaller species. Our results suggest weather-driven environmental variation influences the competitive equilibrium between ecologically similar mammals of differential body size. Whether future climate change leads to the competitive exclusion of either species will likely depend on the mechanism(s) explaining the coexistence of these competing species. Divergent body size and, hence, differences in thermal tolerance and giving up densities offer potential explanations for the weather-dependent competitive asymmetry we documented, especially if the larger species competitively excludes the smaller species from habitat patches of shared preference via interference.

Weather-dependent changes in habitat use by Alpine chamois

BACKGROUND

Alterations in weather patterns due to climate change are accelerated in alpine environments, but mountains also provide a wide range of niches and potential refuge areas. In order to identify future critical habitat for mountain ungulates for effective protection, it is important to understand their spatial responses to changing weather conditions without movement constraints by human disturbance.

METHODS

Using integrated step selection functions, we investigated fine-scale changes in seasonal habitat use in response to weather and time of day for 55 GPS-collared adult Alpine chamois in summer and 42 individuals in winter in a strictly protected area.

RESULTS

Chamois reacted to increasing precipitation and wind speeds primarily by moving to lower elevations in summer and winter. However, reactions to high summer temperatures predominantly involved preferences for increasing tree cover density and northerly slopes. Snow depth had little effect on habitat choice, and southerly slopes were preferred in winter regardless of temperature. At night, chamois moved to steeper slopes and lower elevations than during daytime in both seasons, and to more open areas in summer. Steeper slopes were also preferred with increasing tree cover density.

CONCLUSIONS

Chamois employ adaptive fine-scale adjustments in their habitat choice consistent with respect to efficient thermoregulation and protection from both weather extremes and predation risk in summer and winter. Movement responses to climate change are therefore expected to be far more complex than simple altitudinal changes in distribution. Particularly the role of forest cover must not be underestimated, as it appears to provide important thermal refuge habitat from high summer temperatures.

Insect communities under skyglow: diffuse night-time illuminance induces spatio-temporal shifts in movement and predation

Artificial light at night (ALAN) is predicted to have far-reaching consequences for natural ecosystems given its influence on organismal physiology and behaviour, species interactions and community composition. Movement and predation are fundamental ecological processes that are of critical importance to ecosystem functioning. The natural movements and foraging behaviours of nocturnal invertebrates may be particularly sensitive to the presence of ALAN. However, we still lack evidence of how these processes respond to ALAN within a community context. We assembled insect communities to quantify their movement activity and predation rates during simulated Moon cycles across a gradient of diffuse night-time illuminance including the full range of observed skyglow intensities. Using radio frequency identification, we tracked the movements of insects within a fragmented grassland Ecotron experiment. We additionally quantified predation rates using prey dummies. Our results reveal that even low-intensity skyglow causes a temporal shift in movement activity from day to night, and a spatial shift towards open habitats at night. Changes in movement activity are associated with indirect shifts in predation rates. Spatio-temporal shifts in movement and predation have important implications for ecological networks and ecosystem functioning, highlighting the disruptive potential of ALAN for global biodiversity and the provision of ecosystem services. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Biophysical models accurately characterize the thermal energetics of a small invasive passerine bird

Effective management of invasive species requires accurate predictions of their invasion potential in different environments. By considering species' physiological tolerances and requirements, biophysical mechanistic models can potentially deliver accurate predictions of where introduced species are likely to establish. Here, we evaluate biophysical model predictions of energy use by comparing them to experimentally obtained energy expenditure (EE) and thermoneutral zones (TNZs) for the common waxbill Estrilda astrild, a small-bodied avian invader. We show that biophysical models accurately predict TNZ and EE and that they perform better than traditional time-energy budget methods. Sensitivity analyses indicate that body temperature, metabolic rate, and feather characteristics were the most influential traits affecting model accuracy. This evaluation of common waxbill energetics represents a crucial step toward improved parameterization of biophysical models, eventually enabling accurate predictions of invasion risk for small (sub)tropical passerines.

Areas of spatial overlap between common bottlenose dolphin, recreational boating, and small-scale fishery: management insights from modelling exercises

Background

Sustainable management requires spatial mapping of both species distribution and human activities to identify potential risk of conflict. The common bottlenose dolphin (Tursiops truncatus) is a priority species of the European Union Habitat Directive, thus, to promote its conservation, the understanding of habitat use and distribution, as well as the identification and spatial trend of the human activities which may directly affect populations traits, is pivotal.

Methods

A MaxEnt modeling approach was applied to predict the seasonal (from April to September) habitat use of a small population of bottlenose dolphins in the north-western Sardinia (Mediterranean Sea) in relation to environmental variables and the likelihoods of boat and fishing net presence. Then, the overlapping areas between dolphin, fishing net and boat presence were identified to provide insights for the marine spatial management of this area.

Results

Three of the main factors influencing the seasonal distribution of bottlenose dolphins in the area are directly (boating and fishing) or indirectly (ocean warming) related to human activities. Furthermore, almost half of the most suitable area for dolphins overlapped with areas used by fishing and boating. Finally, relying on fishing distribution models, we also shed light on the potential impact of fishing on the Posidonia oceanica beds, a protected habitat, which received higher fishing efforts than other habitat types.

Discussion

Modelling the spatial patterns of anthropogenic activities was fundamental to understand the ecological impacts both on cetacean habitat use and protected habitats. A greater research effort is suggested to detect potential changes in dolphin habitat suitability, also in relation to ocean warming, to assess dolphin bycatch and the status of target fish species, and to evaluate sensitive habitats conditions, such as the Posidonia oceanica meadow.

Thermoregulation, Not Just Camouflage: The Unique Vasculature of Giraffe Patches. A Cadaver Study with Clinical Implications

BACKGROUND

Serendipitously, a dead giraffe provided opportunity to study its vascular anatomy. Comparative animal studies have revealed important information for designing new flaps and new microsurgical techniques. So, do giraffe's patches support a thermal window concept, do animals with similar markings and habitat have a similar thermoregulatory role, and could results offer new insight into human thermoregulation and free tissue transfer?

METHODS

Previously described lead-oxide arterial-only injection studies, of a single giraffe, zebra, Africa wild dog, and spotted jaguar, all with wire-encircled pigmented patches; and archival human, pig, dog, cat, and rabbit studies, were compared.

RESULTS

Each giraffe patch was supplied by just a single artery (angiosome) averaging 0.9 mm diameter, that divided near its center and sent dense, long, parallel, radiating spoke-wheel branches averaging 0.62 mm diameter to the patch margin, continuing as reduced-caliber choke anastomoses averaging 0.8 mm to link adjacent patch angiosomes. Uniquely arranged large veins, with an average of 1.66 mm, encircled the patches in the pale skin paralleled by arteriae comitantes averaging 0.22 mm. These arteries, connected to patch angiosomes, filled the veins intermittently by means of arteriovenous (A-V) shunts averaging 0.12 mm in diameter of magnitude never seen before in any species studied. None of the other three animals had angiosome territories matching their pigmented fur, or significant A-V filling.

CONCLUSIONS

This study supports the "thermostatic" concept of the giraffe skin patches, with A-V shunts playing a major role. It affirms the need for further studies of these shunts in human thermoregulation and other flow regulations in physiology, pathology, and free tissue transfer.

Temminck pangolins relax the precision of body temperature regulation when resources are scarce in a semi-arid environment

Climate change is impacting mammals both directly (for example, through increased heat) and indirectly (for example, through altered food resources). Understanding the physiological and behavioural responses of mammals in already hot and dry environments to fluctuations in the climate and food availability allows for a better understanding of how they will cope with a rapidly changing climate. We measured the body temperature of seven Temminck's pangolins (Smutsia temminckii) in the semi-arid Kalahari for periods of between 4 months and 2 years. Pangolins regulated body temperature within a narrow range (34-36°C) over the 24-h cycle when food (and hence water, obtained from their prey) was abundant. When food resources were scarce, body temperature was regulated less precisely, 24-h minimum body temperatures were lower and the pangolins became more diurnally active, particularly during winter when prey was least available. The shift toward diurnal activity exposed pangolins to higher environmental heat loads, resulting in higher 24-h maximum body temperatures. Biologging of body temperature to detect heterothermy, or estimating food abundance (using pitfall trapping to monitor ant and termite availability), therefore provide tools to assess the welfare of this elusive but threatened mammal. Although the physiological and behavioural responses of pangolins buffered them against food scarcity during our study, whether this flexibility will be sufficient to allow them to cope with further reductions in food availability likely with climate change is unknown.

The metamicrobiome: key determinant of the homeostasis of nutrient recycling

The metamicrobiome is an integrated concept to study carbon and nutrient recycling in ecosystems. Decomposition of plant-derived matter by free-living microbes and fire - two key recycling pathways - are highly sensitive to global change. Mutualistic associations of microbes with plants and animals strongly reduce this sensitivity. By solving a fundamental allometric trade-off between metabolic and homeostatic capacity, these mutualisms enable continued recycling of plant matter where and when conditions are unfavourable for the free-living microbiome. A diverse metamicrobiome - where multiple plant- and animal-associated microbiomes complement the free-living microbiome - thus enhances homeostasis of ecosystem recycling rates in variable environments. Research into metamicrobiome structure and functioning in ecosystems is therefore important for progress towards understanding environmental change.

Exploiting morphobiometric and genomic variability of African indigenous camel populations-A review

Camels (Camelus dromedarius) in Africa are adapted to arid and the semi-arid environmental conditions, and are valuable for meat, milk and fiber production. On account of the growing demand for camels in this continent, there is a need for knowledge on their phenotypic and genetic diversity. This is fundamental to sustainable herd management and utilization including the design of appropriate breeding and conservation strategies. We reviewed studies on the phenotypic and genetic characterization, breeding objectives, systems of production, productive and reproductive performances, and pathways for the sustainable rearing and use of camels in Africa. The morphological and genetic diversity, productive and reproductive abilities of African camels suggest the existence of genetic variations that can be utilized for breeds/ecotypes' genetic improvement and conservation. Possible areas of intervention include the establishment of open nucleus and community-based breeding schemes and utilization of modern reproductive technologies for the genetic improvement of milk and meat yields, sustainable management of rangelands, capacity building of the pastoralists and agro-pastoralists, institutional supports, formation of centralized conservation centres and efficient and effective marketing systems.

Effects of dehorning on population productivity in four Namibia sub-populations of black rhinoceros (Diceros bicornis bicornis)

The black rhinoceros (rhino) (Diceros bicornis) is critically endangered, with poaching being one of several threats to the species’ survival. Many reserves across several countries, including Namibia, South Africa, and Zimbabwe, now dehorn their rhinos in an attempt to reduce poaching. Historical data collected by the Namibian Ministry of Environment, Forestry, and Tourism and Save the Rhino Trust were used to investigate whether dehorning has an effect on age at first reproduction (AFR), inter-calving interval (ICI), birth sex ratios, calf survival, cause of death, and lifespan. These were assessed in four Namibian sub-populations (hereafter referred to as ‘populations’) of black rhino (denoted A, B, C, and D) which have undergone varying levels of dehorning. No significant difference was found in any of the variables between dehorned and horned individuals. Population was a significant predictor of AFR (LRT = 7.433, p = 0.024) and ICI (LRT = 13.281, p = 0.004), although pairwise comparisons only found populations A and B to be significantly different (AFR: z = −2.736, p = 0.017, ICI: z = −3.705, p = 0.001). Additionally, a significantly higher number of males than females were born in population D (p = 0.021, CI = 0.544, 0.960). The main cause of death across all individuals was poaching, although there was no significant difference in the proportion of rhinos poached between dehorned and horned individuals (X² = 0.638, p = 0.424, n = 265). No evidence was found to suggest that dehorning has any effect on AFR, ICI, birth sex ratios, calf survival, or lifespan in the black rhino, which is reassuring in the continued use of dehorning as an anti-poaching technique in this species.

Habitat restoration is the greatest challenge for population recovery of Hainan gibbons (Nomascus hainanus)

Hainan gibbons are among the world's most critically endangered primates, with a remaining population of only 35 individuals distributed across 5 social groups in the Bawangling Branch of the Hainan Tropical Rainforest National Park, China. Habitat conversion and forest fragmentation over the past 40 years have reduced their geographical distribution by 95%. In the absence of a quantitative assessment of the availability of remaining suitable habitat, it is unclear whether this species can survive to the end of this century. We used behavioral observations, ArcGIS, remote sensing, stereo optical imagery, and MaxEnt modeling to identify patterns of Hainan gibbon range use and compare changes in the distribution of suitable forest types and areas of forest fragmentation over the past 20 years (2000-2020). The results indicate that the combined range of the 5 extant Hainan gibbon groups totaled 14.89 km² . The home range of the smallest group (Group E, 3 individuals) was 1.51 km² , which likely represents the minimum home range size for this species. The remaining area of highly suitable and moderately suitable habitat totals 26.9 km² . However, habitat connectivity across the gibbon range is very low (less than 0.5), limiting the ability of Hainan gibbons to move between forest patches. The results of this study indicate that the availability of suitable habitat in Bawangling is insufficient to allow for future Hainan gibbon population growth. Therefore, immediate action must be taken to restore, reforest, and establish ecological corridors to reconnect areas of suitable habitat for these critically endangered gibbons.

Modeling climate change impacts on the distribution of an endangered brown bear population in its critical habitat in Iran

Climate change is one of the major challenges to the current conservation of biodiversity. Here, by using the brown bear, Ursus arctos, in the southernmost limit of its global distribution as a model species, we assessed the impact of climate change on the species distribution in western Iran. The mountainous forests of Iran are inhabited by small and isolated populations of brown bears that are prone to extinction in the near future. We modeled the potential impact of climate change on brown bear distribution and habitat connectivity by the years 2050 and 2070 under four representative concentration pathways (RCPs) of two general circulation models (GCMs): BCC-CSM1-1 and MRI-CGCM3. Our projections revealed that the current species' range, which encompasses 6749.8 km² (40.8%) of the landscape, will decline by 10% (2050: RCP2.6, MRI-CGCM3) to 45% (2070: RCP8.5, BCC-CSM1-1). About 1850 km² (27.4%) of the current range is covered by a network of conservation (CAs) and no-hunting (NHAs) areas which are predicted to decline by 0.64% (2050: RCP2.6, MRI-CGCM3) to 15.56% (2070: RCP8.5, BCC-CSM1-1) due to climate change. The loss of suitable habitats falling within the network of CAs and NHAs is a conservation challenge for brown bears because it may lead to bears moving outside the CAs and NHAs and result in subsequent increases in the levels of bear-human conflict. Thus, re-evaluation of the network of CAs and NHAs, establishing more protected areas in suitable landscapes, and conserving vital linkages between habitat patches under future climate change scenarios are crucial strategies to conserve and manage endangered populations of the brown bear.

Interspecific Asymmetries in Behavioral Plasticity Drive Seasonal Patterns of Temporal Niche Partitioning in an Island Carnivore Community

Animals vary considerably in the amount of behavioral plasticity they exhibit in daily activity timing and temporal niche switching. It is not well understood how environmental factors drive changes in temporal activity or how interspecific differences in the plasticity of activity timing ultimately manifest in free-living animals. Here, we investigated the temporal structure and organization of activity patterns of two insular mammalian carnivores living in sympatry, the island fox (Urocyon littoralis) and island spotted skunk (Spilogale gracilis amphiala). Using collar-mounted accelerometers, we assessed the plasticity of behavioral activity rhythms in foxes and skunks by investigating how environmental factors drive the distribution of locomotor activity across the day and year, and subsequently examined the dynamics of temporal niche overlap between the two species. We documented that foxes express phenotypic plasticity in daily activity timing across the year, ranging from nocturnal to diurnal to crepuscular rhythms depending on individual and time of year. Most notably, foxes increased the proportion of daytime activity as seasonal temperatures decreased. Overall, activity patterns of foxes were consistent with the circadian thermoenergetics hypothesis, which posits that animals that switch their patterns of activity do so to coincide with the most energetically favorable time of day. In contrast to foxes, skunks exhibited little behavioral plasticity, appearing strictly nocturnal across the year. While the duration of skunk activity bouts increased with the duration of night, timing of activity onset and offset extended into daytime hours during summer when the duration of darkness was shortest. Analysis of temporal niche overlap between foxes and skunks suggested that niche overlap was highest during summer and lowest during winter and was dictated primarily by temporal niche switching in foxes, rather than skunks. Collectively, our results highlight how interspecific asymmetries in behavioral plasticity drive dynamic patterns of temporal niche overlap within an island carnivore community.

Selective Brain Cooling: A New Horizon of Neuroprotection

Therapeutic hypothermia (TH), which prevents irreversible neuronal necrosis and ischemic brain damage, has been proven effective for preventing ischemia-reperfusion injury in post-cardiac arrest syndrome and neonatal encephalopathy in both animal studies and clinical trials. However, lowering the whole-body temperature below 34°C can lead to severe systemic complications such as cardiac, hematologic, immunologic, and metabolic side effects. Although the brain accounts for only 2% of the total body weight, it consumes 20% of the body's total energy at rest and requires a continuous supply of glucose and oxygen to maintain function and structural integrity. As such, theoretically, temperature-controlled selective brain cooling (SBC) may be more beneficial for brain ischemia than systemic pan-ischemia. Various SBC methods have been introduced to selectively cool the brain while minimizing systemic TH-related complications. However, technical setbacks of conventional SBCs, such as insufficient cooling power and relatively expensive coolant and/or irritating effects on skin or mucosal interfaces, limit its application to various clinical settings. This review aimed to integrate current literature on SBC modalities with promising therapeutic potential. Further, future directions were discussed by exploring studies on interesting coping skills in response to environmental or stress-induced hyperthermia among wild animals, including mammals and birds.

Higher Maximum Temperature Increases the Frequency of Water Drinking in Mountain Gorillas (Gorilla beringei beringei)

Water plays a vital role in many aspects of sustaining life, including thermoregulation. Given that increasing temperatures and more extreme weather events due to climate change are predicted to influence water availability, understanding how species obtain and use water is critical. This is especially true for endangered species in small isolated populations which are vulnerable to drought and the risk of extinction. We examined the relationship between the frequency of water drinking and maximum temperature and rainfall in 21 groups of wild gorillas from the two mountain gorilla populations (Bwindi and Virunga), between 2010 and 2020. In both populations, we found that the frequency of water drinking significantly increased at higher maximum temperatures than cooler ones, but we found no consistent relationship between water drinking and rainfall. We also found that Virunga gorillas relied more on foods with higher water content than Bwindi gorillas, which in part likely explains why they drink water much less frequently. These findings highlight that even in rainforest mammals that gain most of their water requirements from food, access to free-standing water may be important because it likely facilitates evaporative cooling in response to thermoregulatory stress. These results have important implications for conservation and behavior of mountain gorillas in the face of continued increases in temperature and frequency of extreme weather events associated with climate change.

The Adrenal Cortisol Response to Increasing Ambient Temperature in Polar Bears (Ursus maritimus)

Our objective was to identify the upper ambient temperature threshold that triggers an increase in cortisol in response to increased thermoregulatory demands in polar bears. The results reported here include endocrine data collected over two years from 25 polar bears housed in 11 accredited zoological institutions across North America. The effects of ambient temperature, sex, age group (juvenile, adult, elderly), breeding season and humidity on fecal cortisol metabolite (FCM) concentrations (N = 8439 samples) were evaluated using linear mixed models. Ambient temperatures were placed into five different categories: <5 °C, 6−10 °C, 11−15 °C, 16−20 °C, and >20 °C. Ambient temperature and humidity had a significant (p < 0.05) effect on FCM concentrations with significant (p < 0.05) interactions of sex, age and breeding season. Once biotic factors were accounted for, there was a significant (p < 0.05) increase in FCM concentrations associated with ambient temperatures above 20 °C in adult polar bears. The implications of these findings for the management of both zoo and wild polar bears are discussed.

Limited Physiological Compensation in Response to an Acute Microclimate Change in a Malagasy Bat

Rapid environmental changes are challenging for endothermic species because they have direct and immediate impacts on their physiology by affecting microclimate and fundamental resource availability. Physiological flexibility can compensate for certain ecological perturbations, but our basic understanding of how species function in a given habitat and the extent of their adaptive scope is limited. Here we studied the effect of acute, experimental microclimate change on the thermal physiology of two populations of the widespread Malagasy bat, Macronycteris commersoni. Populations of this species are found roosting under contrasting conditions, i.e., in a constant hot and humid cave or below foliage unprotected from fluctuations in ambient conditions. We exposed free-ranging individuals of each population to the respective opposite condition and thus to novel microclimate within an ecologically realistic scope while measuring metabolic rate and skin temperature. Cave bats in forest setting had a limited capacity to maintain euthermia to the point that two individuals became hypothermic when ambient temperature dropped below their commonly experienced cave temperature. Forest bats on the other hand, had difficulties to dissipate heat in the humid cave set-up. The response to heat, however, was surprisingly uniform and all bats entered torpor combined with hyperthermia at temperatures exceeding their thermoneutral zone. Thus, while we observed potential for flexible compensation of heat through “hot” torpor, both populations showed patterns suggestive of limited potential to cope with acute microclimate changes deviating from their typically occupied roosts. Our study emphasizes that intraspecific variation among populations could be misleading when assessing species’ adaptive scopes, as variation may arise from genetic adaptation, developmental plasticity or phenotypic flexibility, all of which allow for compensatory responses at differing time scales. Disentangling these mechanisms and identifying the basis of variation is vital to make accurate predictions of species’ chances for persisting in ever rapidly changing habitats and climates.

Complementary evolution of coding and noncoding sequence underlies mammalian hairlessness

Body hair is a defining mammalian characteristic, but several mammals, such as whales, naked mole-rats, and humans, have notably less hair. To find the genetic basis of reduced hair quantity, we used our evolutionary-rates-based method, RERconverge, to identify coding and noncoding sequences that evolve at significantly different rates in so-called hairless mammals compared to hairy mammals. Using RERconverge, we performed a genome-wide scan over 62 mammal species using 19,149 genes and 343,598 conserved noncoding regions. In addition to detecting known and potential novel hair-related genes, we also discovered hundreds of putative hair-related regulatory elements. Computational investigation revealed that genes and their associated noncoding regions show different evolutionary patterns and influence different aspects of hair growth and development. Many genes under accelerated evolution are associated with the structure of the hair shaft itself, while evolutionary rate shifts in noncoding regions also included the dermal papilla and matrix regions of the hair follicle that contribute to hair growth and cycling. Genes that were top ranked for coding sequence acceleration included known hair and skin genes KRT2, KRT35, PKP1, and PTPRM that surprisingly showed no signals of evolutionary rate shifts in nearby noncoding regions. Conversely, accelerated noncoding regions are most strongly enriched near regulatory hair-related genes and microRNAs, such as mir205, ELF3, and FOXC1, that themselves do not show rate shifts in their protein-coding sequences. Such dichotomy highlights the interplay between the evolution of protein sequence and regulatory sequence to contribute to the emergence of a convergent phenotype.

Nameer. The diel activity pattern of small carnivores of Western Ghats, India: a case study at Nelliampathies in Kerala, India

The diel activity pattern of small carnivores was studied using the camera trap technique at Nelliampathy Reserve Forest, Kerala, India. Six species of small carnivores were recorded during the study. These include Brown Palm Civet Paradoxurus jerdoni, Small Indian Civet Viverricula indica, Stripe-necked Mongoose Herpestes vitticollis, Brown Mongoose Herpestes fuscus, Nilgiri Marten Martes gwatkinsii, and Leopard Cat Prionailurus bengalensis.  The maximum diel activity overlap was detected between the Brown Palm Civet and Small Indian Civet, while the activity overlap was minimal between the Stripe-necked Mongoose and Small Indian Civet. 

Temperature induces activity reduction in a Neotropical ungulate

Because global climate change results in increasingly extreme temperatures and more frequent droughts, behavioral thermoregulation is one avenue by which species may adjust. Changes in activity patterns in response to temperature have been observed in a number of mammal species, but rarely have been investigated in humid tropical habitats. Here we examine the relationship between activity patterns and microclimate temperatures for white-lipped peccaries (Tayassu pecari, Tayassuidae, Cetartiodactyla) in four distinct biomes—the Cerrado, the Pantanal, the Atlantic Forest, and the Amazon. From 2013 to 2017, we monitored 30 white-lipped peccaries fitted with GPS collars that included accelerometers and temperature sensors. White-lipped peccaries were primarily diurnal, with peaks of activity in the morning and late afternoon, except in the Amazon where activity was high throughout the day. Total time active did not vary seasonally. White-lipped peccaries were significantly less likely to be active as temperatures increased, with the probability of being active decreasing by &gt;49% in all biomes between 30 and 40°C. Our findings indicate that white-lipped peccaries are likely to be adversely impacted by rising temperatures, through being forced to reduce foraging time during their prime active periods.

Mammalian body size is determined by interactions between climate, urbanization, and ecological traits

Anthropogenically-driven climate warming is a hypothesized driver of animal body size reductions. Less understood are effects of other human-caused disturbances on body size, such as urbanization. We compiled 140,499 body size records of over 100 North American mammals to test how climate and human population density, a proxy for urbanization, and their interactions with species traits, impact body size. We tested three hypotheses of body size variation across urbanization gradients: urban heat island effects, habitat fragmentation, and resource availability. Our results demonstrate that both urbanization and temperature influence mammalian body size variation, most often leading to larger individuals, thus supporting the resource availability hypothesis. In addition, life history and other ecological factors play a critical role in mediating the effects of climate and urbanization on body size. Larger mammals and species that utilize thermal buffering are more sensitive to warmer temperatures, while flexibility in activity time appears to be advantageous in urbanized areas. This work highlights the value of using digitized, natural history data to track how human disturbance drives morphological variation.

Anthropogenically-driven climate change is responsible for body size decreases in mammals. Using an important dataset of historically-collected data and data from continental-scale survey efforts from the National Ecological Observatory Network, Hantak et al. show that urbanization plays an important role in mediating this dynamic.

Food intake: an overlooked driver of climate change casualties?

Reduced voluntary food intake is a common response of endotherms to warmer temperatures. However, the implications of this are rarely considered for wild animals exposed to higher temperatures caused by climate change. We provide a conceptual model to demonstrate the potential consequences of elevated temperatures on food intake and survival.

Heat Stress and Goat Welfare: Adaptation and Production Considerations

This review attempted to collate and synthesize information on goat welfare and production constraints during heat stress exposure. Among the farm animals, goats arguably are considered the best-suited animals to survive in tropical climates. Heat stress was found to negatively influence growth, milk and meat production and compromised the immune response, thereby significantly reducing goats' welfare under extensive conditions and transportation. Although considered extremely adapted to tropical climates, their production can be compromised to cope with heat stress. Therefore, information on goat adaptation and production performance during heat exposure could help assess their welfare. Such information would be valuable as the farming communities are often struggling in their efforts to assess animal welfare, especially in tropical regions. Broadly three aspects must be considered to ensure appropriate welfare in goats, and these include (i) housing and environment; (ii) breeding and genetics and (iii) handling and transport. Apart from these, there are a few other negative welfare factors in goat rearing, which differ across the production system being followed. Such negative practices are predominant in extensive systems and include nutritional stress, limited supply of good quality water, climatic extremes, parasitic infestation and lameness, culminating in low production, reproduction and high mortality rates. Broadly two types of methodologies are available to assess welfare in goats in these systems: (i) animal-based measures include behavioral measurements, health and production records and disease symptoms; (ii) resources based and management-based measures include stocking density, manpower, housing conditions and health plans. Goat welfare could be assessed based on several indicators covering behavioral, physical, physiological and productive responses. The important indicators of goat welfare include agonistic behavior, vocalization, skin temperature, body condition score (BCS), hair coat conditions, rectal temperature, respiration rate, heart rate, sweating, reduced growth, reduced milk production and reduced reproductive efficiency. There are also different approaches available by which the welfare of goats could be assessed, such as naturalistic, functional and subjective approaches. Thus, assessing welfare in goats at every production stage is a prerequisite for ensuring appropriate production in this all-important species to guarantee optimum returns to the marginal and subsistence farmers.

How dryland mammals will respond to climate change: the effects of body size, heat load and a lack of food and water

Mammals in drylands are facing not only increasing heat loads but also reduced water and food availability as a result of climate change. Insufficient water results in suppression of evaporative cooling and therefore increases in body core temperature on hot days, while lack of food reduces the capacity to maintain body core temperature on cold nights. Both food and water shortage will narrow the prescriptive zone, the ambient temperature range over which body core temperature is held relatively constant, which will lead to increased risk of physiological malfunction and death. Behavioural modifications, such as shifting activity between night and day or seeking thermally buffered microclimates, may allow individuals to remain within the prescriptive zone, but can incur costs, such as reduced foraging or increased competition or predation, with consequences for fitness. Body size will play a major role in predicting response patterns, but identifying all the factors that will contribute to how well dryland mammals facing water and food shortage will cope with increasing heat loads requires a better understanding of the sensitivities and responses of mammals exposed to the direct and indirect effects of climate change.

Regularities in species' niches reveal the world's climate regions

Climate regions form the basis of many ecological, evolutionary, and conservation studies. However, our understanding of climate regions is limited to how they shape vegetation: they do not account for the distribution of animals. Here, we develop a network-based framework to identify important climates worldwide based on regularities in realized niches of about 26,000 tetrapods. We show that high-energy climates, including deserts, tropical savannas, and steppes, are consistent across animal- and plant-derived classifications, indicating similar underlying climatic determinants. Conversely, temperate climates differ across all groups, suggesting that these climates allow for idiosyncratic adaptations. Finally, we show how the integration of niche classifications with geographical information enables the detection of climatic transition zones and the signal of geographic and historical processes. Our results identify the climates shaping the distribution of tetrapods and call for caution when using general climate classifications to study the ecology, evolution, or conservation of specific taxa.

Potential role of specific microRNAs in the regulation of thermal stress response in livestock

Thermal stress is known to have harmful effects on livestock productivity and can cause livestock enterprises considerable financial loss. These effects may be aggravated by climate change. Stress responses to nonspecific systemic actions lead to perturbation of molecular pathways in the organism. The molecular response is regulated in a dynamic and synchronized manner that assurances robustness and flexibility for the restoration of functional and structural homeostasis in stressed cells and tissues. MicroRNAs (miRNAs) are micro molecules of small non-coding RNA that control gene expression at the post-transcriptional level. Recently, various studies have discovered precise types of miRNA that regulate cellular machinery and homeostasis under various types of stress, suggesting a significant role of miRNA in thermal stress responses in animals. The miRNAs revealed in this paper could serve as promising candidates and biomarkers for heat stress and could be used as potential pharmacological targets for mitigating the consequences of thermal stress. Stress miRNA pathways may be associated with thermal stress, which offers some potential approaches to combat the negative impacts of thermal stress in livestock. The review provides new data that can assist the elucidation of the miRNA mechanisms that mediate animals' responses to thermal stress.

Field data confirm the ability of a biophysical model to predict wild primate body temperature

In the face of climate change there is an urgent need to understand how animal performance is affected by environmental conditions. Biophysical models that use principles of heat and mass transfer can be used to explore how an animal's morphology, physiology, and behavior interact with its environment in terms of energy, mass and water balances to affect fitness and performance. We used Niche Mapper™ (NM) to build a vervet monkey (Chlorocebus pygerythrus) biophysical model and tested the model's ability to predict core body temperature (T_b) variation and thermal stress against T_b and behavioral data collected from wild vervets in South Africa. The mean observed T_b in both males and females was within 0.5 °C of NM's predicted T_bs for 91% of hours over the five-year study period. This is the first time that NM's T_b predictions have been validated against field data from a wild endotherm. Overall, these results provide confidence that NM can accurately predict thermal stress and can be used to provide insight into the thermoregulatory consequences of morphological (e.g., body size, shape, fur depth), physiological (e.g. T_b plasticity) and behavioral (e.g., huddling, resting, shade seeking) adaptations. Such an approach allows users to test hypotheses about how animals adapt to thermoregulatory challenges and make informed predictions about potential responses to environmental change such as climate change or habitat conversion. Importantly, NM's animal submodel is a general model that can be adapted to other species, requiring only basic information on an animal's morphology, physiology and behavior.

Temperature as a constraint on the timing and duration of African elephant foraging trips

In arid and semiarid environments, water is a key resource that is limited in availability. During the dry season, perennial water sources such as water pans often are far apart and shape the daily movement routines of large herbivores. In hot environments, endotherms face a lethal risk of overheating that can be buffered by evaporative cooling. Behavioral adjustments are an alternative way to reduce thermal constraints on the organism. The trade-off between foraging and reaching water pans has been studied widely in arid environments; however, few studies have looked into how ambient temperature shapes individual trips between two visits to water. In this study, we tracked during the dry season the movement of eight GPS-collared African elephants (Loxodonta africana) cows from different herds in Hwange National Park, Zimbabwe. This species, the largest extant terrestrial animal, is particularly sensitive to heat due to its body size and the absence of sweat glands. We show that most foraging trips depart from water at nightfall, lowering the average temperature experienced during walking. This pattern is conserved across isolated elephant populations in African savannas. We also observed that higher temperatures at the beginning of the trip lead to shorter trips. We conclude that elephants adjust the timing of foraging trips to reduce the thermal constraints, arguing that further considerations of the thermal landscape of endotherms are important to understand their ecology.

Infrared thermography cannot be used to approximate core body temperature in wild primates

Understanding the physiological processes that underpin primate performance is key if we are to assess how a primate might respond when navigating new and changing environments. Given the connection between a mammal's ability to thermoregulate and the changing demands of its thermal environment, increasing attention is being devoted to the study of thermoregulatory processes as a means to assess primate performance. Infrared thermography can be used to record the body surface temperatures of free-ranging animals. However, some uncertainty remains as to how these measurements can be used to approximate core body temperature. Here, we use data collected from wild vervet monkeys (Chlorocebus pygerythrus) to examine the relationship between infrared body surface temperature, core body (intra-abdominal) temperature, and local climate, to determine to what extent surface temperatures reflect core body temperature. While we report a positive association between surface and core body temperature-a finding that has previously been used to justify the use of surface temperature measurements as a proxy for core temperature regulation-when we controlled for the effect of the local climate in our analyses, this relationship was no longer observed. That is, body surface temperatures were solely predicted by local climate, and not core body temperatures, suggesting that surface temperatures tell us more about the environment a primate is in, and less about the thermal status of its body core in that environment. Despite the advantages of a noninvasive means to detect and record animal temperatures, infrared thermography alone cannot be used to approximate core body temperature in wild primates.

Mapping Shade Availability and Use in Zoo Environments: A Tool for Evaluating Thermal Comfort

For many species in zoos, particularly megafauna vulnerable to heat stress, shade is a key environmental resource. However, shade availability has received comparatively less attention than other aspects of the zoo environment. In this study, we share a simple low-cost approach that we applied to document shade availability across 33 zoo enclosures. We then combined these assessments with behavioral observations of enclosure use and shade-seeking behavior during summer months in a case study focused on Sichuan takin (Budorcas taxicolor tibetana) (n = 3), a large cold-adapted bovid. Behavioral observations were conducted before and after installation of a shade sail for the takin. Results indicated that shade availability varied widely across zoo enclosures, with the percent of shaded space ranging from 85 % to 22 % across enclosures during summer months. Shade was a dynamic resource and increased throughout the year and fluctuated across the day, with the least shade available midday. Takin showed general preferences for shaded areas near the walls of their enclosure but were observed using newly available shade from the shade sail after its installation. These accessible methods can be easily applied to assess shade within existing enclosures, evaluate enclosure modifications, and provide guidance for the design of new enclosures.

Increased Diurnal Activity Is Indicative of Energy Deficit in a Nocturnal Mammal, the Aardvark

Shifting activity to cooler times of day buffers animals from increased heat and aridity under climate change. Conversely, when resources are limited, some nocturnal species become more diurnal, reducing energetic costs of keeping warm at night. Aardvarks (Orycteropus afer) are nocturnal, obligate ant- and termite-eating mammals which may be threatened directly by increasing heat and aridity, or indirectly by the effects of climate change on their prey. We hypothesised that the minimum 24-h body temperature of aardvarks would decline during energy scarcity, and that aardvarks would extend their active phases to compensate for reduced resource availability, possibly resulting in increased diurnal activity when aardvarks were energetically compromised. To measure their thermoregulatory patterns and foraging activity, we implanted abdominal temperature and activity data loggers into 12 adult aardvarks and observed them for varying durations over 3 years in the Kalahari. Under non-drought conditions, aardvarks tightly controlled their 24-h body temperature rhythm (mean amplitude of the 24-h body temperature rhythm was 1.8 ± 0.3°C during summer and 2.1 ± 0.1°C during winter) and usually were nocturnal. During a summer drought, aardvarks relaxed the precision of body temperature regulation (mean 24-h amplitude 2.3 ± 0.4°C) and those that subsequently died shifted their activity to progressively earlier times of day in the weeks before their deaths. Throughout the subsequent winter, the aardvarks’ minimum 24-h body temperatures declined, causing exaggerated heterothermy (4.7 ± 1.3°C; absolute range 24.7 to 38.8°C), with one individual’s body temperature varying by 11.7°C within 8 h. When body temperatures were low, aardvarks often emerged from burrows during daytime, and occasionally returned before sunset, resulting in completely diurnal activity. Aardvarks also shortened their active periods by 25% during food scarcity, likely to avoid energetic costs incurred by foraging. Despite their physiological and behavioural flexibility, aardvarks were unable to compensate for reduced food availability. Seven study aardvarks and several others died, presumably from starvation. Our results do not bode well for aardvarks facing climate change, and for the many animal species dependent on aardvark burrows for refuge.

Predation risk constrains herbivores' adaptive capacity to warming

Global warming compels larger endothermic animals to adapt either physiologically or behaviourally to avoid thermal stress, especially in tropical ecosystems. Their adaptive responses may however be compromised by other constraints, such as predation risk or starvation. Using an exceptional camera-trap dataset spanning 32 protected areas across southern Africa, we find that intermediate-sized herbivores (100-550 kg) switch activity to hotter times of the day when exposed to predation by lions. These herbivores face a tight window for foraging activity being exposed to nocturnal predation and to heat during the day, suggesting a trade-off between predation risk and thermoregulation mediated by body size. These findings stress the importance of incorporating trophic interactions into climate change predictions.