Abstract
We present a Dynamic Energy Budget (DEB) model for the quintessential keystone predator, the rocky-intertidal sea star Pisaster ochraceus. Based on first principles, DEB theory is used to illuminate underlying physiological processes (maintenance, growth, development, and reproduction), thus providing a framework to predict individual-level responses to environmental change. We parameterized the model for P. ochraceus using both data from the literature and experiments conducted specifically for the DEB framework. We devoted special attention to the model’s capacity to (1) describe growth trajectories at different life-stages, including pelagic larval and post-metamorphic phases, (2) simulate shrinkage when prey availability is insufficient to meet maintenance requirements, and (3) deal with the combined effects of changing body temperature and food supply. We further validated the model using an independent growth data set. Using standard statistics to compare model outputs with real data (e.g. Mean Absolute Percent Error, MAPE) we demonstrated that the model is capable of tracking P. ochraceus’ growth in length at different life-stages (larvae: MAPE = 12.27%; post-metamorphic, MAPE = 9.22%), as well as quantifying reproductive output index. However, the model’s skill dropped when trying to predict changes in body mass (MAPE = 24.59%), potentially because of the challenge of precisely anticipating spawning events. Interestingly, the model revealed that P. ochraceus reserves contribute little to total biomass, suggesting that animals draw energy from structure when food is limited. The latter appears to drive indeterminate growth dynamics in P. ochraceus. Individual-based mechanistic models, which can illuminate underlying physiological responses, offer a viable framework for forecasting population dynamics in the keystone predator Pisaster ochraceus. The DEB model herein represents a critical step in that direction, especially in a period of increased anthropogenic pressure on natural systems and an observed recent decline in populations of this keystone species.
Highlights
Improving our ability to anticipate responses of natural systems to environmental change is among the most pressing challenges facing modern ecological theory [1]
Exploiting the virtues of Dynamic Energy Budget (DEB) theory, we describe a model that can (1) predict Pisaster growth at larval and post-metamorphic stages when prey are abundant and available ad libitum, (2) characterize shrinkage when food is removed, and (3) illuminate dynamics in physiological processes driven by cumulative effects of temperature and prey availability
Model training results DEB model parameter values for Pisaster were successfully estimated through the covariation method using data from both, experiments conducted to determine DEB quantities and from the literature (Table 1)
Summary
Improving our ability to anticipate responses of natural systems to environmental change is among the most pressing challenges facing modern ecological theory [1]. The physiological responses of individuals may be considered as the underlying basis of all ecological dynamics, providing a solid foundation for advancing the field of ecological forecasting [1]. Promising are bioenergetics studies that quantify flows of energy and mass through an individual, which in turn dictate levels of physiological performance including feeding, growth and reproduction. This provides a mechanistic framework that can help characterize physiological responses to current and projected environmental drivers as a consequence, for example, of increasing temperatures [10]
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