A general framework for jointly modelling thermal and hydric constraints on developing eggs

Abstract

Abstract Eggs are a vulnerable stage because they are sensitive to thermal and hydric conditions and yet cannot behaviourally avoid stressful environments. A general mechanistic model of egg development in natural nests requires microclimatic predictions of temperature, humidity, radiation (if above ground) and water potential (if buried in soil) to be integrated with models of heat and water exchange of the egg and the metabolism of the developmental process. Although all the required pieces for such a model now exist, they have not been integrated into a general modelling framework. We developed such an integration using NicheMapR package for mechanistic niche modelling. Specifically, we took an existing general model of egg water exchange and connected it with the microclimate model in NicheMapR to simulate nest thermal and hydric environments, including the effects of soil water potential on liquid and vapour exchange and moisture‐mediated soil thermal conductivity on heat exchange. We then used the Dynamic Energy Budget model within the ectotherm model of NicheMapR as the mechanistic engine for the developmental process, allowing the explicit computation of the dynamics of metabolic heat production and all aspects of mass exchange. We illustrate the modelling framework using existing laboratory and field data on reptiles, insects, and birds. We show that it can capture laboratory observations of water exchange and metabolic heat production and how it can be used to map potential development and water uptake under natural conditions at the continental scale. The modelling framework can be used to interpret laboratory experiments and allows strong inferences to be made about the abiotic constraints on egg development in natural nests under past, present, and future environmental change.