Islet lizards can learn to evade feral cats

Island species are disproportionally at risk for extinction, since they have no adaptations against exotic predators such as feral cats (Felis silvestris catus). A new study shows that naïve island lizards may be highly susceptible to cats, and yet their ancestral anti-predator defenses could help them adapt to these new and future threats.

Cats have been on the Aegean islands since the Bronze Age. Now, a team led by Binbin Li from Duke University examined the impact of feral cats on common Aegean wall lizards (Podarcis erhardii) on the large island of Naxos and four of its cat-free satellite islets: Ovriokastro, Aspronissi, Parthenos, and Mando. On Naxos, lizard densities were more than twice as high in areas with lower cat densities — no surprise there. But the findings also show that the long-term presence of cats has led lizards to flee sooner and escape more effectively.

During the summer of 2011, the team recorded flight initiation distance (FID) — the distance from its predator at which an animal will try to escape — from at least 30 lizards living in dry stone walls at each of the sites. Lizards from populations exposed to cats generally stayed closer to refuges, and they had higher FIDs than lizards unaccustomed to cats. The researchers also compared how easily the lizards shed their tails, a trick used to distract predators or escape their grasp. Because intact tails help with social status, locomotion, and lipid storage, the cost of readily losing a tail may outweigh the benefits if there are few predators around. Indeed, lizards from high cat density locales shed their tails with more ease than the others.

Podarcis erhardii

Lastly, the scientists pushed a black decoy cat mounted on a platform with wheels toward the lizards. Unlike skittish lizards on Naxos, about 60 percent of the islet lizards didn’t run for shelter at all when they saw the cat decoy, and 70 percent actually approached the decoy before fleeing. However, their FIDs did increase with further cat decoy encounters, which suggests the lizards could quickly regain their ancient defensive responses to cope with feline threats.

That’s good news, because the loss of anti-predator behavior can happen fast. Mando just became its own island during a storm in 2006, and already its lizards are slower to drop their tails. — Janet Fang | 19 June 2014

Source: Li, B. et al. Effects of feral cats on the evolution of anti-predator behaviours in island reptiles: insights from an ancient introduction, Proceedings of the Royal Society B (2014). doi: 10.1098/rspb.2014.0339

Images: PhotolisticLife via shutterstock (top) & Podarcis erhardii by Arie van der Meijden CC BY-NC-SA 3.0