An agent-based bioenergetics model for predicting impacts of environmental change on a top marine predator, the Weddell seal

Abstract

One of the crucial scientific challenges of this century is characterizing the vulnerability of ecosystems to climate change. Bioenergetics models can provide a theoretical construct for addressing specific physiological and ecological hypotheses about how individuals may respond; however, many models fail to link energy deficiencies with reproductive consequences, and thus cannot be used to predict population-level impacts. Here, we present an agent-based, ecophysiological model that simulates the energy balance of adult, female Weddell seals (Leptonychotes weddellii). The input parameters include physiological values and population-wide ranges for the duration and phenology of life history events. Energy intake depends on foraging effort and stochastic prey availability, whereas energy expenditure is calculated from time- and behavior-specific demands. The simulated seal selects an activity (forage, nurse pup, molt, rest) based on body condition and life history constraints. At the end of each timestep, the energy budget is balanced, and catabolism or anabolism occurs. Following model development and validation with empirical data, simulations were run to study the responses of individuals to: (1) baseline conditions; and (2) reduced prey availability. As expected, the model replicated the known fluctuations in energetic requirements associated with reproduction and molt. A 10% reduction in prey availability resulted in seals foraging more and resting less. At the end of the year-long simulations, animals in the baseline simulation had significantly higher body masses than animals in the perturbation simulation. The model was successfully used to explore decision-based energy allocation strategies that occur under different energetic stressors and to elucidate how extrinsic conditions can impact individual fitness. Identifying the temporal sensitivities of Weddell seals to predicted anthropogenic changes is a valuable contribution to the study of global change biology and can inform management decisions in polar regions.