Abstract
Robust ecological forecasting requires accurate predictions of physiological responses to environmental drivers. Energy budget models facilitate this by mechanistically linking biology to abiotic drivers, but are usually ground-truthed under relatively stable physical conditions, omitting temporal/spatial environmental variability. Dynamic Energy Budget (DEB) theory is a powerful framework capable of linking individual fitness to environmental drivers and we tested its ability to accommodate variability by examining model predictions across the rocky shore, a steep ecotone characterized by wide fluctuations in temperature and food availability. We parameterized DEB models for co-existing mid/high-shore (Mytilus galloprovincialis) and mid/low-shore (Perna perna) mussels on the south coast of South Africa. First, we assumed permanently submerged conditions, and then incorporated metabolic depression under low tide conditions, using detailed data of tidal cycles, body temperature and variability in food over 12 months at three sites. Models provided good estimates of shell length for both species across the shore, but predictions of gonadosomatic index were consistently lower than observed. Model disagreement could reflect the effects of details of biology and/or difficulties in capturing environmental variability, emphasising the need to incorporate both. Our approach provides guidelines for incorporating environmental variability and long-term change into mechanistic models to improve ecological predictions.
Highlights
Improving our understanding and predictions of species responses to environmental variability requires mechanistic approaches capable of disentangling the relative and interacting effects of multiple drivers[1]
Environmental variability can reduce the predictive power of energy budget models, and variability deserves special consideration when working with taxa subject to wide fluctuations in food and temperature, as recently highlighted for terrestrial and semi-aquatic species[18,19]
This study examines the application of Dynamic Energy Budget (DEB) models across the environmental stress gradient offered among shore levels using two model species: the mussels Perna perna and Mytilus galloprovincialis
Summary
Improving our understanding and predictions of species responses to environmental variability requires mechanistic approaches capable of disentangling the relative and interacting effects of multiple drivers[1]. Classic energy budget models such as scope for growth have provided a means of quantifying the energy allocation and physiological state of organisms subject to specific biotic and abiotic conditions[5]. Such models are informative of species’ adaptive capacities[6], they are usually only applicable to the conditions defined by the experimental design. Despite the capacity of DEB theory to incorporate contrasting physical conditions, the models are usually built and implemented for species/populations that experience relatively homogeneous environments, in terms of food and temperature. As almost all intertidal species are of marine origins, this results in a dramatic increase in physiological stress from low- to high-shore levels[22]
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