Evolution of antipredator behavior in an island lizard species: the sum of all fears?

Brock, K. M., Bednekoff, P. A., Pafilis, P., & Foufopoulos, J. (2014). Evolution of antipredator behavior in an island lizard species, Podarcis erhardii (Reptilia: Lacertidae): the sum of all fears?. Evolution.

Organisms generally have many defenses against predation yet may lack effective defenses if from populations without predators. Evolutionary theory predicts that ‘costly’ antipredator behaviors will be selected against when predation risk diminishes. We examined antipredator behaviors in Aegean wall lizards, Podarcis erhardii, across an archipelago of land-bridge islands that vary in predator diversity and period of isolation. We examined two defenses, flight initiation distance and tail autotomy. Flight initiation distance generally decreased with declining predator diversity. All predator types had distinctive effects on flight initiation distance with mammals and birds having the largest estimated effects. Rates of autotomy observed in the field were highest on predator-free islands yet laboratory-induced autotomy increased linearly with overall predator diversity. Against expectation from previous work, tail autotomy was not explained solely by the presence of vipers. Analyses of populations directly isolated from rich predator communities revealed that flight initiation distance decreased with increased duration of isolation in addition to the effects of current predator diversity, whereas tail autotomy could be explained simply by current predator diversity. Although selection against costly defenses should depend on time with reduced threats, different defenses may diminish along different trajectories even within the same predator-prey system.

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Effects of feral cats on the evolution of antipredator behavior in the Aegean wall lizard

Li, B. (2012). Effects of feral cats on the evolution of antipredator behaviors in the Aegean wall lizard Podarcis erhardii (Doctoral dissertation, University of Michigan).

Exotic predators such as feral cats (Felis catus), have been the driving force behind the extinction of many endemic species of island mammals, birds and reptiles. Island endemics appear to be exceptionally susceptible to invasive predators because of small population size and frequent lack of anti-predator defenses. The goal of this study was to determine the impacts of feral cats on the island populations of Aegean Wall lizards (Podarcis erhardii, Lacertidae) in relationship to the expression of anti-predator behaviors. I estimated lizard population densities in areas with low cat density sites (LCD) versus high cat density (HCD) sites by conducting 100-m transect along dry-stone walls, on the island of Naxos, as well as on surrounding islets (Cyclades, Greece). Degree of expression of antipredator behaviors was determined by measuring flight initiation distance (FID) and rates of tail autotomy both in the field and in the lab for six populations in HCD, LCD sites and four satellite islets without cat presence. I also staged controlled encounters with mounted cats decoys and quantified escaping responses from lizards from these populations. I found that feral cats had a strong negative effect on lizard population densities. Lizards adapted their antipredator behaviors in response to cat predation by extending their FIDs, increasing their capacity for tail autotomy, and by staying closer to refugia. In laboratory predation simulations, lizards from cat-free islets had significantly shorter FIDs than LCD site lizards and in particular than HCD site lizards. Furthermore, some unique islet behaviors, presumably evolved in response to lack of predators and to ameliorate chronic conditions of food shortage, appear to render islet lizards strongly susceptible to cat predation. These behaviors include rarely utilizing available refugia, and moving towards anything new, including cat decoys. Nonetheless, I found that repeated exposures over three trials led to significant increases in FIDs for all populations, indicating at least some behavioral plasticity. My results suggest that although lizards may adapt their antipredator behaviors to cope with introduced predators, this offers at best only partial protection, so that there remains strong concern about their survival in the face of expanding feral cat populations.


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Study shows impact of feral cats on lizards in Greek Islands

 Male of Erhard's Wall Lizard (Podarcis erhardii) . 

Credit: Jeroen Speybroeck/Wikipedia

A team of researchers with diverse backgrounds from universities in the U.S. and Greece has conducted a study of the impact of feral cats on Aegean wall lizards living in the Cyclades (Greek islands). In their paper published in Proceedings of the Royal Society B: Biological Sciences, the team describes behavior adaptations they observed in native lizards to the presence of feral cats.

Feral cats are domestic cats that are living in the wild—reports over the past several years have implicated them in a number of extinctions and declines of other species, particularly birds. Another type of creature impacted by feral cats is lizards—cats are known to kill them whether they eat them or not. In this new study, the research team ventured to the Thera, Kea and Naxos islands in the Cyclades—where cats were introduced by humans approximately 9,500 years ago—to learn more about how the native lizards have adapted to the introduced threat.

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Anti-cat behaviour in island reptiles

Li, B., Belasen, A., Pafilis, P., Bednekoff, P., & Foufopoulos, J. (2014). 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: Biological Sciences, 281(1788), 20140339.

Exotic predators have driven the extinction of many island species. We examined impacts of feral cats on the abundance and anti-predator behaviours of Aegean wall lizards in the Cyclades (Greece), where cats were introduced thousands of years ago. We compared populations with high and low cat density on Naxos Island and populations on surrounding islets with no cats. Cats reduced wall lizard populations by half. Lizards facing greater risk from cats stayed closer to refuges, were more likely to shed their tails in a standardized assay, and fled at greater distances when approached by either a person in the field or a mounted cat decoy in the laboratory. All populations showed phenotypic plasticity in flight initiation distance, suggesting that this feature is ancient and could have helped wall lizards survive the initial introduction of cats to the region. Lizards from islets sought shelter less frequently and often initially approached the cat decoy. These differences reflect changes since islet isolation and could render islet lizards strongly susceptible to cat predation.