Behavior and temperature modulate a thermoregulation–predation risk trade‐off in juvenile gopher tortoises. (9th November 2017) - Radzio, Thomas A.
Abstract: Ectotherms frequently thermoregulate behaviorally to improve physiological processes such as digestion and growth, but basking and other thermoregulatory activities can also increase predation risk. Organismal and environmental characteristics can, in some species, influence predation risk associated with thermoregulation and thereby relax or tighten constraints on thermoregulatory behavior, physiological performance, and, ultimately, life history traits. Providing one of the first such investigations in turtles, we examine whether behavior and thermal environment modulate a thermoregulation–predation risk trade‐off in juvenile gopher tortoises ( Gopherus polyphemus ). Young gopher tortoises experience very high predation pressure, and their declining species faces many challenges, including human‐induced increased shading of its environment. We hypothesized that in response to simulated predator approach, basking hatchling and juvenile tortoises would: (i) hide inside burrows; (ii) hide for shorter durations in cooler burrows presumably due to greater constraints on physiological performance; and (iii) spend greater time at the surface following disturbance in cool environments because individuals would need to bask more to maintain preferred body temperatures. Basking tortoises always hid inside burrows when approached and exhibited very long flight initiation distances ( x ¯ = 45 m) that increased with age/size. Individuals fled into burrows even when it was not possible for them to see the approaching researcher, suggesting the use of vibrations (aerial/ground) to detect potential predators and a possible antipredator function for exceptionally large otoliths characteristic of the species. Tortoises hid for short durations ( x ¯ = 18.3 min), especially in cool burrows, suggesting that they optimize hiding responses to balance physiological costs and antipredator benefits. Additionally, surface activity following disturbance consisted primarily of basking and correlated negatively with burrow temperature. These findings suggest that thermal environment influences predation risk in ectotherms whose surface activity is driven primarily by thermoregulatory requirements and highlight potential benefits of warm, well‐insolated habitats, such as endangered longleaf pine ( Pinus palustris ) ecosystems, for juvenile gopher tortoises.