Estimating inter-individual variability of dynamic energy budget model parameters for the copepod Nitocra spinipes from existing life-history data

The degree of biological variability within a population is an important factor for its ecological success. Yet, individual-based population models (IBMs) that utilize the Dynamic Energy Budget (DEB) theory as a mechanistic basis to simulate an individual's life history, largely rely on rule-of-thumb estimates of inter-individual variability of their parameter values. In this study, we explored how data from previous life-history experiments with the copepod Nitocra spinipes could be used to make realistic estimates of variability in DEB parameter values for this species. We specifically investigated to which one of 12 possible parameters variability should be added, and what shape and scale its probability distribution should have, to most accurately reproduce the experimental data's variation with model simulations. The best result was achieved by drawing the parameter ‘surface-area-specific maximum assimilation rate’ from a log-normal distribution with a standard deviation of 0.15 or by drawing the maturity thresholds for birth and puberty (assuming proportionality between the two) from a log-normal distribution with a standard deviation of 0.40. In both cases, the model not only accurately reproduced the variation observed in development time data (which had been used in the fitting process) but also gave adequate predictions of the variation observed in brood size data (which had not been used for fitting). Although the findings of this study apply to one species only, the methods presented here are a proof of principle for how the question of intra-specific variability in a DEB model, for any species, can be addressed in a simple, yet purposeful manner.