American Society of Naturalists

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“Upscaling microclimatic conditions into body temperature distributions of ectotherms”

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Juan G. Rubalcaba, Sidney F. Gouveia, and Miguel A. Olalla-Tárraga (May 2019)

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An information-theoretical model to predict body temperature of ectotherms from microclimatic data

Agamid lizard basking in the morning near its burrow (Rumuruti, Kenya). <br />(Credit: Juan G. Rubalcaba)
Agamid lizard basking in the morning near its burrow (Rumuruti, Kenya).
(Credit: Juan G. Rubalcaba)

A current challenge for quantitative ecologists is to forecast the organismal responses to climate change. This task requires developing models to predict, for example, how increasing ambient temperatures actually influence body temperature of individuals and their potential to adapt to novel climatic conditions. Many cold-blooded animals (such as invertebrates, frogs, or lizards) can control their body temperatures by exploiting the heterogeneity of their environment, choosing among sunny or shaded areas, basking sites or burrows. Using models to predict the response of cold-blooded animals to climate change is challenging because they require a vast amount of information to compute microhabitat preferences and physiological and behavioral features of species for which this information is often lacking. So far, there is no general model capable of dealing with uncertain information and still making accurate predictions on the actual body temperature of cold-blooded animals from climatic data.

A team of researchers from Spain and Brazil has taken a step further in breaking this barrier by developing a model capable of predicting body temperature of lizards in the field. The model uses principles of information theory and statistical mechanics from physics to derive the most probable allocation scheme of individuals among the repertoire of microhabitats (e.g., sun, shade, burrows). Then, using a thermodynamic model, it computes the actual body temperature in a probabilistic way. Further, their model quantifies the importance of active control of body temperature for cold-blooded animals, for example, through avoiding exposure to sun radiation during the central hours of the day. In addition to providing a novel theoretical framework for understanding and simulating thermoregulation of cold-blooded animals, this study makes a first step towards reliable projections of organismal responses to future climates.


Abstract

Realistic projections of the biological impacts of climate change require predicting fitness responses to variations in environmental conditions. For ectotherms, this challenge requires methods to scale-up microclimatic information into actual body temperatures, Tb, while dealing with uncertainty regarding individual behaviors and physiological constraints. Here, we propose an information-theoretical model to derive microhabitat selection and Tb distributions of ectotherm populations from microclimatic data. The model infers the most probable allocation of individuals among the available microenvironments and the associated population-level Tb distribution. Using empirical Tb data of 41 species of desert lizards from three independently evolved systems – Western North America, Kalahari Desert, and Western Australia – we show that the model accurately predicts empirical Tb distributions across the three systems. Moreover, the framework naturally provides a way to quantify the importance of thermoregulation in a thermal environment and thereby a measurement for the constraint imposed by the climatic conditions. By predicting Tb distribution of ectotherm populations, even without exhaustive information on the underpinning mechanisms, our approach forms a solid theoretical basis for upscaling microclimatic and physiological information into a population-level fitness trait. This scaling process is a first step to reliably project the biological impacts of climate change to broad temporal and spatial scales.

Escalando condiciones microclimáticas en distribuciones de temperatura corporal de ectotermos

Para predecir de manera fiable los impactos bióticos del cambio climático, es necesario predecir cómo la eficacia biológica responde a variaciones en las condiciones ambientales. En ectotermos, este reto requiere de métodos que permitan escalar información microclimática a temperaturas corporales reales, Tb, y al mismo tiempo lidiar con la incertidumbre derivada de comportamientos individuales y limitantes fisiológicas. En este trabajo, proponemos un modelo basado en teoría de la información que permite calcular la preferencia de microhábitats y distribuciones de Tb de poblaciones de ectotermos a partir de datos microclimáticos. El modelo infiere la distribución espacial más probable de los individuos entre los microambientes disponibles y la distribución de Tb a nivel de población. Utilizando datos empíricos de Tb de 41 especies de lagartos de desierto provenientes de tres sistemas independientes –oeste de Norteamérica, Desierto del Kalahari y oeste de Australia– mostramos que el modelo logra predecir con precisión las distribuciones de Tb a través de los tres sistemas. Además de esto, el método permite cuantificar la importancia de la termorregulación en un ambiente térmico y con ello, aportar una medida de las restricciones térmicas impuestas por las condiciones climáticas. Al predecir la distribución de Tb de poblaciones de ectotermos, aún en ausencia de información exhaustiva de los mecanismos subyacentes, nuestro modelo aporta una base teórica sólida para estimar un rasgo relacionado con la eficacia biológica a nivel poblacional a partir de información microclimática y fisiológica. Este es un primer paso para predecir de manera fiable los impactos bióticos del cambio climático a escalas espaciales y temporales amplias.