A key challenge in ecology is to define species' niches on the basis of functional traits. Size and shape are important determinants of a species' niche but their causal role is often difficult to interpret. For endotherms, size and shape define the thermal niche through their interaction with core temperature, insulation, and environmental conditions, determining the thermoneutral zone (TNZ) where energy and water costs are minimized. Laboratory measures of metabolic rate used to describe TNZs cannot be generalized to infer the capacity for terrestrial animals to find their TNZ in complex natural environments. Here, we derive an analytical model of the thermal niche of an ellipsoid furred endotherm that accurately predicts field and laboratory data. We use the model to illustrate the relative importance of size and shape on the location of the TNZ under different environmental conditions. The interaction between body shape and posture strongly influences the location of the TNZ and the expected scaling of metabolic rate with size at constant temperature. We demonstrate that the latter relationship has a slope of approximately ½ rather than the commonly expected surface area/volume scaling of ⅔. We show how such functional traits models can be integrated with spatial environmental datasets to calculate null expectations for body size clines from a thermal perspective, aiding mechanistic interpretation of empirical clines such as Bergmann's Rule. The combination of spatially explicit data with biophysical models of heat exchange provides a powerful means for studying the thermal niches of endotherms across climatic gradients.

Understanding what determines a species' range is a central objective in ecology and evolutionary biology. It has important applications for predicting species distributions and how they might respond to environmental perturbations. This paper describes a mechanistic approach to predict past and present distribution of the Japanese serow (Capricornis crispus) on Honshu, Japan. We applied state‐of‐the‐art microclimate and animal biophysical/behavioral models coupled with climate and vegetation data to estimate the distribution of potential range expansion under protection. We tested the model results against detailed empirical distribution data from the Ministry of the Environment for a five‐prefecture area in central Honshu. We also applied the models to time‐series land use/cover maps to investigate the historical transitions in habitat suitability during 1947–1999 in the Arai‐Keinan region. This is the first time to our knowledge that mechanistic models have successfully predicted the landscape scale distribution of a mammal species in the absence of other animal species interactions, such as predators. In this case, animal energetics/behavior–plant interactions seem to be critical. Forest cover appears to be important in summer and winter for suitable serow habitats. The energetics model results indicate that the serow can overheat in some open environments in midday hours in summer. In winter, simulation results suggested that forest cover provides effective refuge to avoid increased metabolic demands of cold temperatures and strong winds. The model simulations suggested that land use/cover changes documented during 1947–1999 resulted in increased suitable serow habitat due to expanding forest cover from agricultural marginalization and ecological succession. The models provide a unique tool for estimating species' range expansion under protection or for selecting suitable reintroduction sites.

Assisted colonization—the deliberate translocation of species from unsuitable to suitable regions—is a controversial management tool that aims to prevent the extinction of populations that are unable to migrate in response to climate change or to survive in situ. The identification of suitable translocation sites is therefore a pressing issue. Correlative species distribution models, which are based on occurrence data, are of limited use for site selection for species with historically restricted distributions. In contrast, mechanistic species distribution models hold considerable promise in selecting translocation sites. Here we integrate ecoenergetic and hydrological models to assess the longer-term suitability of the current habitat of one of the world’s rarest chelonians, the Critically Endangered Western Swamp Tortoise (Psuedemydura umbrina). Our coupled model allows us to understand the interaction between thermal and hydric constraints on the foraging window of tortoises, based on hydrological projections of its current habitat. The process can then be repeated across a range of future climates to identify regions that would fall within the tortoise’s thermodynamic niche. The predictions indicate that climate change will result in reduced hydroperiods for the tortoises. However, under some climate change scenarios, habitat suitability may remain stable or even improve due to increases in the heat budget. We discuss how our predictions can be integrated with energy budget models that can capture the consequences of these biophysical constraints on growth, reproduction and body condition.

This study uses a spatially explicit microclimate/biophysical approach to examine the potential distribution of the Po'ouli on Maui to find either new habitats to search for existence or refine search efforts in previously occupied areas. We used specific physiological and behavioral ecology bird data, and Po'ouli morphological and spectral data obtained from museum specimens to address ecological and conservation-related questions about the Po'ouli that are otherwise very difficult to quantify. Laboratory and field tested microclimate and biophysical—behavioral animal computer models were integrated with remote sensing technologies. To show that the generic microclimate and endotherm models can predict metabolic and water loss requirements of Hawaiian Honeycreepers, we used the 2 species with known physiological properties, the Hawaiian Amakihi, Hemignathus virens, and the Hawaiian Anianiau, Hemignathus parvus. Predictions were within experimental measurement error of the laboratory measurements. Then using field rather than laboratory conditions as input data, we predict the field distribution of the Amakihi on Maui as the first spatial test of the models applied to birds. Results are consistent with Amakihi field distribution data. Fossils show that the Po'ouli once lived on Maui at low elevations in dry/mesic habitats on a likely diet of native tree snails and insects. The arrival of lethal mosquito-borne avian malaria in Hawaii exterminated low elevation Po'ouli forcing a population shift to mountain rainforests and possibly a snail diet instead of insects. To explore the maximum consequences of such a diet shift we assumed exclusive diets of snails versus insects at both low and high elevations. Snail diets require ∼4 times higher foraging rates than do insect diets, making a predominantly snail diet an unlikely prospect for the Po'ouli. Landscape scale simulations suggest that a snail diet would force a Po'ouli distribution inconsistent with observations. A predominantly insect diet is consistent with distribution observations. We show that as local environmental conditions change across the landscape in space and diurnal/seasonal time it is possible to quantify animal physiological and behavioral consequences of those variations in their local environment. This enables quantification of the requisite spatial and temporal distribution and amount or availability of resources that may affect species' potential for survival, growth, reproduction and distribution.

Summary: A future warmer climate is generally predicted to threaten reptiles. But many high‐altitude reptiles that rely on external heat to survive current cold climate may benefit from future warmth. This prediction can be tested by simulating activity time and energetics of reptiles with a biophysical model. We modelled the potential response of a high‐altitude snake, Trimeresurus gracilis, to a 3 °C increase in air temperature, using the biophysical/behavioural NicheMapper^™ model. Using animal and environmental properties, we first analysed the effects of shade level (i.e. the reduction of solar radiation) on activity time and energetics of T. gracilis. We then computed activity time, energetics and potential habitats in its current range of Taroko National Park, Taiwan (>1800 m in altitude), with a spatial climate, vegetation and topography data set. In the current climate, increased shade levels were predicted to decrease activity time, maintenance energy requirements and discretionary energy (i.e. energy left after maintenance costs are met). In heavy shade (i.e. 81–100% reduction of solar radiation) at 3000 and 3500 m, T. gracilis was predicted to have impaired digestive capacity and hence to be unable to meet basic maintenance costs for survival. In a warmer climate, the predicted digestive capacity, energetics and activity time of T. gracilis increase. But in heavy shade at 3500 m, the digestive capacity was predicted to remain impaired for supporting basic energy requirements for survival. In the current climate, the predicted suitable habitat area (i.e. where T. gracilis obtains positive discretionary energy) in coniferous and coniferous–broadleaf forests decreased with increasing elevation. At elevations higher than 3000 m, most suitable habitats were in open areas like grasslands where T. gracilis was also predicted to have more discretionary energy than in heavily forested habitats. Our field sightings agreed with model predictions. A warmer climate was generally predicted to increase the activity time, energetics and habitat area, given the current vegetation pattern. Overall, we demonstrate that metabolism, digestive function and vegetative shade levels are critical elements affecting T. gracilis' energetics and habitats with climate change. Trimeresurus gracilis is likely to benefit energetically from future warmth.