Patterns of predation and antipredator behavior in the Australian water dragon, Physignathus Lesueurii

Although lizards are more diverse in arid environments, many lizard taxa have independently invaded aquatic habitats. Adaptations in aquatic lizards are often straightforward (e.g., dorsolaterally compressed tails facilitate swimming), but what made these species invade aquatic habitats in the first place? Although this question is not directly testable, one possible reason is to reduce predation risk. Here we examine the fit of a species’ antipredator behaviors to the predation risk associated with its known and suspected predators. We reviewed the literature for records of predation on the Australian Water Dragon, Physignathus lesueurii, a semi-aquatic lizard that uses aquatic escape and aquatic sleeping, but does not forage underwater. We then examined these two behaviors in relation to the patterns of predation revealed by our review. Our review identified 25 species of predators, most of which were aerial (mainly raptors) or terrestrial/arboreal (snakes, lizards, and mammals). Aquatic predators were rare. Our review supports the hypothesis that Water Dragons invaded and persist in aquatic habitats to decrease predation risk from terrestrial and aerial predators, although we cannot rule out the exploitation of an abundance of available (riparian) food as the primary reason for invading aquatic habitats. Future studies should test how well Water Dragons can thermoregulate by sleeping underwater (vs. in air), and could test the antipredator responses of Water Dragons to mock predators.