Thesis defense of Chloé Chabaud

“Influence of water balance on trophic interactions and predation risk in a terrestrial ectothermic mesopredator”

Ongoing climate change is affecting environmental temperatures but also water availability in ecosystems, which may disrupt trophic relationships between prey and predators. In terrestrial ectotherms, there is a conflict between the regulation of body temperature and water balance, but we lack data to characterize the effects of the associated trade-offs on biotic interactions. This thesis addresses this issue through the ecophysiological and behavioural study of traits related to thermo-hydroregulation and trophic relationships in the Common lizard (Zootoca vivipara). This generalist mesopredator feeds on a wide variety of prey and is subject to heavy predation, especially by specialized snakes. Reptiles exhibit a large range of functional traits associated with thermo-hydroregulation, and my work characterizes the individual and geographic determinants of these traits in the Common lizard. Then, using experimental approaches, I demonstrate that water restriction cannot be compensated by food intakes in this species, and food actually exacerbates behavioural conflicts between thermo- and hydroregulation. Through laboratory observations, I also investigate the trade-offs between behavioural hydroregulation and predator avoidance. I show that detecting predators via chemoreception increases water loss and this ability is therefore sensitive to water restriction. This work suggests that the behavioural strategies employed by organisms for thermo-hydroregulation can influence the dynamics of predator-prey relationships.

Key-word: water balance, diet, anti-predator behaviours, physiology, ectotherm, thermo-hydroregulation