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Increases in the frequency, severity and duration of temperature extremes are anticipated in the near future. Although recent work suggests that changes in temperature variation will have disproportionately greater effects on species than changes to the mean, much of climate change research in ecology has focused on the impacts of mean temperature change. Here, we couple fine-grained climate projections (2050–2059) to thermal performance data from 38 ectothermic invertebrate species and contrast projections with those of a simple model. We show that projections based on mean temperature change alone differ substantially from those incorporating changes to the variation, and to the mean and variation in concert. Although most species show increases in performance at greater mean temperatures, the effect of mean and variance change together yields a range of responses, with temperate species at greatest risk of performance declines. Our work highlights the importance of using fine-grained temporal data to incorporate the full extent of temperature variation when assessing and projecting performance.

This short descriptive note updates and summarises knowledge on the breeding phenology of the nocturnal Gekkota Euleptes europaea. A forty-year dataset covering the entire range of the species is provided. Between 1982 and 2024, a total of 39 populations were studied in 85 sampling sessions. Reproduction is highly seasonal, with gravid females appearing from early spring until mid-June when oviposition begins. Hatching occurs from mid-August to early October. This study and the dataset provided will allow further work to assess whether, and to what extent, climate change would affect the breeding phenology of this nocturnal gecko.

Global warming is increasing the overheating risk for many organisms, though the potential for plasticity in thermal tolerance to mitigate this risk is largely unknown. In part, this shortcoming stems from a lack of knowledge about global and taxonomic patterns of variation in tolerance plasticity. To address this critical issue, we test leading hypotheses for broad-scale variation in ectotherm tolerance plasticity using a dataset that includes vertebrate and invertebrate taxa from terrestrial, freshwater and marine habitats. Contrary to expectation, plasticity in heat tolerance was unrelated to latitude or thermal seasonality. However, plasticity in cold tolerance is associated with thermal seasonality in some habitat types. In addition, aquatic taxa have approximately twice the plasticity of terrestrial taxa. Based on the observed patterns of variation in tolerance plasticity, we propose that limited potential for behavioural plasticity (i.e. behavioural thermoregulation) favours the evolution of greater plasticity in physiological traits, consistent with the ‘Bogert effect’. Finally, we find that all ectotherms have relatively low acclimation in thermal tolerance and demonstrate that overheating risk will be minimally reduced by acclimation in even the most plastic groups. Our analysis indicates that behavioural and evolutionary mechanisms will be critical in allowing ectotherms to buffer themselves from extreme temperatures.

Plasticity can allow organisms to maintain consistent performance across a wide range of environmental conditions. However, it remains largely unknown how costly plasticity is and whether a trade-off exists between plasticity and performance under optimal conditions. Biological rates generally increase with temperature, and to counter that effect, fish use physiological plasticity to adjust their biochemical and physiological functions. Zebrafish in the wild encounter large daily and seasonal temperature fluctuations, suggesting they should display high physiological plasticity. Conversely, laboratory zebrafish have been at optimal temperatures with low thermal fluctuations for over 150 generations. We treated this domestication as an evolution experiment and asked whether this has reduced the physiological plasticity of laboratory fish compared to their wild counterparts. We measured a diverse range of phenotypic traits, from gene expression through physiology to behavior, in wild and laboratory zebrafish acclimated to 15 temperatures from 10 °C to 38°C. We show that adaptation to the laboratory environment has had major effects on all levels of biology. Laboratory fish show reduced plasticity and are thus less able to counter the direct effects of temperature on key traits like metabolic rates and thermal tolerance, and this difference is detectable down to gene expression level. Rapid selection for faster growth in stable laboratory environments appears to have carried with it a trade-off against physiological plasticity in captive zebrafish compared with their wild counterparts.

In recent years, ecologists have stepped up to address the challenges imposed by rapidly changing climates. Some researchers have developed niche-based methods to predict how species will shift their ranges. Such methods have evolved rapidly, resulting in models that incorporate physiological and behavioral mechanisms. Despite their sophistication, these models fail to account for environmental heterogeneity at the scale of an organism. We used an individual-based model to quantify the effects of operative environmental temperatures, as well as their heterogeneity and spatial structure, on the thermoregulation, movement, and energetics of ectotherms. Our simulations showed that the heterogeneity and spatial structure of a thermal landscape are as important as its mean temperature. In fact, temperature and heterogeneity interact to determine organismal performance. Consequently, the popular index of environmental quality (d e), which ignores variance and spatial structure, is inherently flawed as a descriptor of the thermal quality of an environment. Future efforts to model species’ distributions should link thermoregulation and activity to environmental heterogeneity at fine scales.

Mechanistic forecasts of how species will respond to climate change are highly desired but difficult to achieve. Because processes at different scales are explicit in such models, careful assessments of their predictive abilities can provide valuable insights that will be relevant to functionally similar species. However, there are surprisingly few comprehensive field tests of mechanistic niche models in the literature. We applied a general, thermodynamically grounded modeling framework to determine the fundamental niche of an extremely well-studied herbivorous ectotherm, the sleepy lizard Tiliqua rugosa. We then compared the model predictions with detailed long-term field observations that included sub-hourly data on microclimate, activity levels, home ranges, and body temperatures as well as annual to decadal patterns of body condition and growth. Body temperature predictions inferred from gridded climatic data were within 10% of empirically observed values and explained >70% of observed daytime activity patterns across all lizards. However, some periods of activity restriction were explained by predicted desiccation level rather than by temperature, and metabolically driven activity requirements were much lower than potential activity time. Decadal trajectories of field growth and body condition could also be explained to within 10% of observed values, with the variance in trajectories being attributable to whether individuals had access to permanent water. Continent-wide applications of the model partly captured the inland distribution limit, but only after accounting for water limitations. Predicted changes in habitat suitability under six climate change scenarios were generally positive within the species' current range, but varied strongly with predicted rainfall. Temperature is regarded as the major factor that will restrict the distribution and abundance of lizards and other terrestrial ectotherms under climate change. Yet our findings show how water can be more important than temperature in constraining the activity, habitat requirements, and distribution limits of terrestrial ectotherms. Our results demonstrate the feasibility of first-principles computation of the climatic limits on terrestrial animals from gridded environmental data, providing a coherent picture for how species will respond to climate change at different scales of space and time.

Thermal performance curves have been widely used to model the ecological responses of ectotherms to variable thermal environments and climate change. Such models ignore the effects of time dependence—the temporal pattern and duration of temperature exposure—on performance. We developed and solved a simple mathematical model for growth rate of ectotherms, combining thermal performance curves for ingestion rate with the temporal dynamics of gene expression and protein production in response to high temperatures to predict temporal patterns of growth rate in constant and diurnally fluctuating temperatures. We used the model to explore the effects of heat shock proteins on larval growth rates of Manduca sexta. The model correctly captures two empirical patterns for larval growth rate: first, maximal growth rate and optimal temperature decline with increasing duration of temperature exposure; second, mean growth rates decline with time in diurnally fluctuating temperatures at higher mean temperatures. These qualitative results apply broadly to cases where proteins or other molecules produced in response to high temperatures reduce growth rates. We discuss some of the critical assumptions and predictions of the model and suggest potential extensions and alternatives. Incorporating time-dependent effects will be essential for making more realistic predictions about the physiological and ecological consequences of temperature fluctuations and climate change.

Aim: General geographical patterns of insect body size are still a matter of considerable debate, mainly because the annual number of generations (voltinism) and its relationship with body size have largely been ignored. We present the first analyses of voltinism and body size of insect assemblages at a continental scale using lepidopteran and odonate species. We hypothesize that voltinism is strongly driven by environmental conditions and constrains body size on macroecological scales. Location: Europe. Methods: We compiled the distribution, voltinism and body size of 943 lepidopteran and odonate species within a 50 km × 50 km grid system, thereby presenting a novel method for estimating the body volume of species from digital images. Regressions and structural equation modelling were applied to distinguish the effects of temperature, productivity and season length on mean voltinism and body size within grid cells. We accounted for spatial autocorrelation with auto regressive models and analysed the possible effect of species richness and intraspecific variability. Results: Voltinism consistently decreased with latitude for both lepidopterans (r² = 0.76) and odonates (r² = 0.86), with species having on average fewer generations per year in northern Europe and more generations per year in southern Europe. The effects of temperature, productivity and season length on body size contrasted in sign between lepidopterans and odonates, leading to opposing geographical patterns across Europe. Main conclusions: Voltinism in insect assemblages is strongly driven by environmental temperature, and trade-offs between voltinism and body size influence the occurrence of species at macroecological scales. Insects with the ability to extend their generation time over multiple years can overcome this constraint, allowing for a relatively large body size in cold areas. Our results furthermore support the idea that body sizes of terrestrial and aquatic insects form contrasting geographical patterns because they are differently affected by temperature and resource constraints.

Research addressing the effects of global warming on the distribution and persistence of species generally assumes that population variation in thermal tolerance is spatially constant or overridden by interspecific variation. Typically, this rationale is implicit in sourcing one critical thermal maximum (CTmax) population estimate per species to model spatiotemporal cross‐taxa variation in heat tolerance. Theory suggests that such an approach could result in biased or imprecise estimates and forecasts of impact from climate warming, but limited empirical evidence in support of those expectations exists. We experimentally quantify the magnitude of intraspecific variation in CTmax among lizard populations, and the extent to which incorporating such variability can alter estimates of climate impact through a biophysical model. To do so, we measured CTmax from 59 populations of 15 Iberian lizard species (304 individuals). The overall median CTmax across all individuals from all species was 42.8°C and ranged from 40.5 to 48.3°C, with species medians decreasing through xeric, climate‐generalist and mesic taxa. We found strong statistical support for intraspecific differentiation in CTmax by up to a median of 3°C among populations. We show that annual restricted activity (operative temperature > CTmax) over the Iberian distribution of our study species differs by a median of >80 hr per 25‐km2 grid cell based on different population‐level CTmax estimates. This discrepancy leads to predictions of spatial variation in annual restricted activity to change by more than 20 days for six of the study species. Considering that during restriction periods, reptiles should be unable to feed and reproduce, current projections of climate‐change impacts on the fitness of ectotherm fauna could be under‐ or over‐estimated depending on which population is chosen to represent the physiological spectra of the species in question. Mapping heat tolerance over the full geographical ranges of single species is thus critical to address cross‐taxa patterns and drivers of heat tolerance in a biologically comprehensive way. En macroecología, cuando se evalúan los efectos del calentamiento global en la distribución y persistencia de las especies, generalmente se asume que la tolerancia térmica entre poblaciones es constante a lo largo de la distribución de las especies, o despreciable en comparación con su variación interespecífica. Tal planteamiento es implícito cuando se utiliza el máximo crítico termal (CTmax) de una población por especie para modelar la variación espacio‐temporal de la tolerancia termal entre especies. Teóricamente, esto puede sesgar o añadir imprecisión en las estimaciones y proyecciones de impacto por el calentamiento asociado al cambio global, pero la evidencia empírica de tales previsiones es limitada. Cuantificamos experimentalmente la magnitud de la variación intraespecífica en CTmax entre poblaciones de lagartijas, y hasta qué punto la incorporación de esta variabilidad puede alterar la evaluación del impacto del clima a través de un modelo biofísico. Para ello, medimos el CTmax en 59 poblaciones de 15 especies de lagartijas ibéricas (304 individuos). La mediana general del CTmax fue 42.8°C entre todos los individuos de todas las especies, y varió desde 40.5 hasta 48.3°C, mientras que las medianas por especie decrecieron de taxones de hábitats secos, pasando por generalistas, hasta taxones de hábitats húmedos. Encontramos un fuerte apoyo estadístico para la diferenciación intraespecífica del CTmax de hasta de 3°C (mediana) entre poblaciones. Mostramos que la actividad restringida anual (temperatura operativa > CTmax) en la distribución ibérica de las especies de estudio difirió en > 80 horas por celda espacial de 25‐km2 (mediana) en función del CTmax poblacional. Esta discrepancia conduce a que las predicciones de la variación espacial de la actividad restringida anual difieran en más de 20 días en seis de las especies investigadas. Teniendo en cuenta que durante los periodos de restricción, los reptiles son incapaces de alimentarse y reproducirse, las proyecciones actuales de impactos del cambio climático sobre el fitness de la fauna ectotérmica pueden infra‐ o sobre‐estimarse dependiendo de la población elegida para representar el espectro fisiológico de cada especie. Cartografiar la tolerancia termal sobre el rango geográfico completo de especies individuales es por lo tanto crucial, antes de que podamos examinar patrones y mecanismos de variación entre múltiples especies de una manera biológicamente comprensiva. In one of the largest field surveys of thermal tolerances undertaken to date (304 individuals, 59 populations, 15 species), the authors show that estimates of climate impact on Iberian lizards differ depending on which population estimate of heat tolerance is taken to represent this trait in a full species.

In ectotherms, growth rate, body size and maturation rate covary with temperature, with the direction and magnitude of variation predicted by the Temperature‐Size Rule (TSR). Nutritional quality or availability of food, however, may vary over latitudinal gradients, resulting in ambiguous effects on body size and maturation rate. The Temperature‐Constraint Hypothesis (TCH) predicts that marine herbivorous ectotherms are nutritionally compromised at latitudes exceeding 30°. This provides an opportunity to resolve the contrasting demographic responses of ectotherms to variation in temperature and nutritional status over latitudinal gradients. This study uses analysis of demographic rates to evaluate the predictions of the TSR in a marine herbivorous ectotherm sampled over a significant latitudinal gradient. The direction and magnitude of demographic variation was established in the marine herbivorous fish, Odax pullus (the butterfish), and compared with that of a phylogenetically related but trophically distinct species, the carnivorous Notolabrus fucicola (the banded wrasse). Both species were sampled at three locations across the length of New Zealand covering latitudes between 35°S and 49°S. Growth rate, mean size‐at‐age, age‐ and size‐at‐maturity, life span and abundance were estimated for each species at each location. Demographic traits of both taxa varied with latitude. Both species showed slower initial growth rates, and matured later at a larger body size at higher latitudes than populations sampled at lower latitudes. In addition, abundances increased significantly at higher latitudes in both species. These results were consistent with the TSR but not with the TCH, confirming that nutritional ecology (herbivore vs. carnivory) did not determine demographic patterns over a biologically significant latitudinal gradient. Results from this study suggest that the absence of herbivorous reef fishes from the higher latitudes of the Northern Hemisphere may not reflect a general physiological mechanism as suggested by the TCH and highlights the need to clarify the evolutionary histories of the marine biota of each hemisphere.