Life in the slow lane? A dynamic energy budget model for the western swamp turtle, Pseudemydura umbrina

Dynamic energy budget (DEB) theory provides a generalised way to quantify how an organism assimilates and utilizes energy throughout its life cycle. Over 800 DEB models have been created to date, typically under the assumption of constant food supply. The Critically Endangered, semi-aquatic western swamp turtle occupies an ephemeral wetland environment in which food resources fluctuate from abundant to absent with the seasonal filling and drying of swamps. Approximately six months of each year are spent in aestivation underground when the swamps are dry and conditions are warm. We estimated DEB parameters for the western swamp turtle with the explicit incorporation of these seasonal fluctuations in food and temperature. A metabolic depression factor was applied during the aestivation stage, without which turtles lost both mass and length, and reserves were insufficient to reach puberty. The swamp turtle had a very high Arrhenius temperature, being almost 2.5-fold greater than that of the other Testudine species for which there are DEB models (typical Arrhenius temperatures are around 8000 K; western swamp turtle is 19,371 K). It also had the second highest somatic maintenance costs of the reptiles in the DEB ‘Add My Pet’ collection, and the highest for Testudines. We explore these results in context of the “waste to hurry” hypothesis, which we suggest may apply for this species. We also consider how a DEB model for this species might be applied in its future conservation and management.