1. Modelling the direction and constraints on the evolution of functional trait in reptiles
We developed biophysical models to predict body temperature and physiological performance of reptiles and used them to investigate how thermal performance varies in response to climate across species with different body sizes, skin colours, thermoregulatory capacity, and physiological tolerance. This global analysis allowed us to numerically predict the direction and strength of selection on different functional traits. To test these predictions, we coordinated different experts in macroecology and thermal physiology and compared predicted vs observed patterns using published data of more than 1200 species of reptiles. We found that models accurately predict the direction and strength of the effect of climate on different functional traits on a global scale.
2. Modelling broad-scale responses of tropical ectotherms to climate change
Many ectotherms such as lizards exploit the heterogeneity of their environments to control body temperature behaviourally, e.g. moving between sun-exposed and shaded microenvironments. Yet, we lack a method to quantify this behavioural buffering capacity on a broad scale. We used our ectotherm biophysical model to evaluate the potential of behavioural thermoregulation to buffer body temperature against climate change in Neotropical, forest-dwelling lizards – a group that is especially vulnerable to warming. We found that the predicted increase in ambient temperature in the Amazon could exceed the estimated maximum buffering capacity of lizards. Our approach allows, for the first time, to compute the capacity of tropical lizards to buffer the impacts of warming – a critical milestone towards designing effective management strategies to reduce the vulnerability of these species to climate and habitat change.
3. Modelling metabolic rate and the response of aquatic ectotherms to climate change
Organismal responses to climate change are mediated through its effects on physiology. In aquatic environments, both water temperature and oxygen availability may modulate these responses by altering the metabolism fuelling physiological performance. However, ecological models aimed at predicting how environmental factors shape aerobic metabolism disregard the role of oxygen supply. We developed a biophysical model to investigate how oxygen uptake capacity affects the response of aquatic ectotherms to climate warming. In a comparative analysis across fish species, we showed that the model accurately predicts complex interactions between body size and temperature on fish aerobic scope. Our results suggest that larger species may be more constrained than smaller species in warming waters due to physical limitations in oxygen uptake capacity.
4. Modelling the costs of thermoregulation in endotherms
Biophysical models of heat balance can estimate the metabolic cost required for an endothermic organism such as a bird or a mammal to maintain constant body temperature in a variable environment. We used biophysical models to address the outstanding question in macroecology of why body size of bats does not follow the geographical and evolutionary patterns observed among non-volant mammals. By modelling the costs of thermoregulation and the costs of flight, we found that these costs likely constrain body size and shape, especially in colder climates. By analysing size and shape of 278 bat species, we found that morphological evolution in bats varies with climate and that the strength of selection is higher in colder than in warmer regions, consistently with the model’s prediction. These results shed light on a longstanding debate over bats’ conformity to macroevolutionary patterns observed in other mammals and offers a novel procedure for investigating complex macroecological patterns from first principles.
5. Organization of workshops and communication activities
A key objective SCALE is to disseminate mechanistic modelling approaches among researchers of different disciplines such as physiology and macroecology, and different systems such as terrestrial and aquatic environments. To achieve this, we organized two workshops presenting the use of microclimate and biophysical models in species distribution modelling and climate change impacts forecasting (IBS 2022, CSEE 2021). In addition, to reach a broader, non-specialist audience, we launched a blog presenting the most relevant results of the project and developed two “Shiny Apps” in R to allow any user to interact with the biophysical models online.
