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Feral cats (that is free-ranging cats that are not in human care) have been introduced to nearly 179.000 islands worldwide, frequently devastating the native wildlife. They have been implicated in the extinctions of approx. 10% of the world’s island species. Although the short-term impact of such cats on island wildlife can be severe, it is important to understand their long-term effects. This study, led by Binbin Li, examined the impacts of feral cats on the reptiles of the Aegean Sea islands, an area where these predators were introduced during the Bronze Age several thousand years ago.
Using a combination of field observations with lab experiments that compared lizard populations across a range of sites, with and without cats, the study showed that cat presence shapes both the population densities and the behavior of native wall lizards. While normally densities of these lizards, which preferentially inhabit dry-stone walls, increased with wall height, in areas with feral cats were present, they were depressed to low levels irrespective of wall height.
In addition, extent of antipredator defenses employed by lizards increased across study sites with elevated cat densities. For example, ease of tail-shedding, a critically important response to predation, increased in areas with cats. Furthermore, in areas with cats, lizards were much shyer and did not venture very far from their hiding spots. Standardized behavioral assays revealed that lizards from small, cat-free islands, were not just unafraid, but would actually approach cat decoys. Nonetheless, a limited number (1-3) of encounters re-established appropriate fear responses, suggesting that such behavioral defenses are quite pliable. (Li et al.; Proc. Royal Soc. of London, 2014)
In low-cat environments, density of lizards (animals/100m) is positively related to the height of a dry-stone wall. When cats are present, they depress lizard populations to an invariant ‘giving-up’ density of approx. 5 indiv./100m of wall.
The distance at which a lizard starts running away from a potential predator (Flight Initiation Distance [FID] [y-axis]) is related to the distance to the nearest hiding place (Distance to Refuge [x-axis]) as well as the perceived predation risk. Lizards in predator-free small islands (far R), roam widely from their hiding places and do not initiate escape until the very last minute. In contrast lizards in areas with high cat densities, are shy and never stray far from their refuge.
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