Abstract
Within pinnipeds, phocids and otariids show differing maternal care strategies. Phocids rear young out of body stores in a yearly cycle with a single stay ashore when the mother fasts while lactating, whereas otariids provision their young by repeated foraging trips to sea alternating with brief stays ashore where they suckle their young. In a previous optimality model, these differences have been interpreted as adaptations based on differing energy requirements of large (phocid) and smaller (otariid) species, and the time budget of the large elephant and the much smaller Antarctic fur seal were correctly predicted. Our refined model—extended to pinniped species of all sizes—predicts lactation strategies to shift from attendance cycles to 1-year cycles with increasing body mass and provides an explanation for the finding that phocid pups are weaned at lower relative mass than otariid pups. However, other predictions do not correspond to empirical findings. In particular, the model does not explain the behavior of large otariids and small phocids. Thus, maternal metabolic requirements alone appear insufficient to explain observed lactation patterns. In the light of our results, we discuss more generally the scope and limitations of optimality models when applied in a comparative framework to a group of related species.
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Acknowledgements
We greatly appreciate the help of Ian Boyd, who provided his original program, discussed the results of our model with FT, and critically read the manuscript. Sasha Dall, Hanna Kokko, and one anonymous reviewer also provided much appreciated criticism of a previous version of the manuscript. Christoph Guinet pointed out diverse aspects of physiological adaptations of pups to the variable schedule of maternal milk transfer. FT would like to thank Rudi Drent and Jan Komdeur for providing room and interesting discussions at the University of Groningen and expresses special thanks to the Theoretical Biology Group at the University of Groningen for a most stimulating stay.
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Trillmich, F., Weissing, F.J. Lactation patterns of pinnipeds are not explained by optimization of maternal energy delivery rates. Behav Ecol Sociobiol 60, 137–149 (2006). https://doi.org/10.1007/s00265-005-0150-4
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DOI: https://doi.org/10.1007/s00265-005-0150-4