Abstract
Antipredatory defenses are maintained when benefit exceeds cost. A weak predation pressure may lead insular lizards to tameness. Podarcis lilfordi exhibits a high degree of insular tameness, which may explain its extinction from the main island of Menorca when humans introduced predators. There are three species of lizards in Menorca: the native P. lilfordi, only on the surrounding islets, and two introduced lizards in the main island, Scelarcis perspicillata and Podarcis siculus. In addition, there are three species of snakes, all introduced: one non-saurophagous (Natrix maura), one potentially non-saurophagous (Rhinechis scalaris) and one saurophagous (Macroprotodon mauritanicus). We studied the reaction to snake chemical cues in five populations: (1) P. lilfordi of Colom, (2) P. lilfordi of Aire, (3) P. lilfordi of Binicodrell, (4) S. perspicillata, and (5) P. siculus, ordered by increasing level of predation pressure. The three snakes are present in the main island, while only R. scalaris is present in Colom islet, Aire and Binicodrell being snake-free islets. We aimed to assess the relationship between predation pressure and the degree of insular tameness regarding scent recognition. We hypothesized that P. lilfordi should show the highest degree of tameness, S. perspicillata should show intermediate responses, and P. siculus should show the highest wariness. Results are clear: neither P. lilfordi nor S. perspicillata recognize any of the snakes, while P. siculus recognizes the scent of M. mauritanicus and reacts to it with typical well-defined antipredatory behaviours as tail waving and slow motion. These results rise questions about the loss of chemical recognition of predators during island tameness and its related costs and benefits for lizards of insular habitats. In addition, this highlights the necessity for strong conservation measures to avoid the introduction of alien predators.
Highlights
Predation is one of the main evolutionary forces for animals
We focus the study on Menorca (Fig. 1), where it is probable that the introduction of alien predators by humans in ancient times led to the extinction of the Balearic lizard on the main island (Pérez-Mellado, 2009; Cooper & Pérez-Mellado, 2012)
We studied three subspecies: (1) P. lilfordi brauni from Colom island, which coexists with Rhinechis scalaris, (2) P. lilfordi lilfordi from the snake-free island of Aire, and (3) P. lilfordi codrellensis from the snake-free island of Binicodrell
Summary
Morphological or behavioural defenses allow them to avoid predators will enhance survival (Endler, 1986; Lima & Dill, 1990). The hunting mechanisms of predators and the defenses of prey usually coevolve in a cost-benefit model (Greene, 1988; Lima & Dill, 1990; Vermeij, 1994; Sih et al, 2010). Insular populations often experience much weaker predation pressures than continental animals, which results in the evolution of tameness, a reduction of antipredatory responses (Darwin, 1839; Curio, 1976; Blumstein & Daniel, 2005). If alien predators had coevolved with similar prey as the naïve ones in their original habitats, the situation could be more dramatic and even result in the extinction of the naïve prey population (Sih et al, 2010; Blackburn et al, 2004)
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