The need for enemy-free space: The impact of an invasive gecko on island endemics

How introduced reptiles cause the loss of endemic reptiles is poorly understood and currently there are no available techniques for dealing with this major conservation issue. We addressed both these problems by investigating the role of the introduced house gecko Hemidactylus frenatus in causing the catastrophic decline and extinction of the endemic night gecko Nactus populations of the Mascarene Islands and how this introduced species can be excluded from habitats on the basis of morphology. Competition for enemy free space was tested in experimental enclosures and showed that H. frenatus displace the endemic Nactus coindemirensis and Nactus durrelli from favoured positions close to and from refugia, thus increasing the risk of predation and exposure to stochastic events. The ability of H. frenatus to grip substrates with their pad-bearing toes was examined, and we demonstrated that naturally occurring substrates with a greater amount of loose surface material of a higher particulate concentration and size excludes H. frenatus, but not Nactus. These findings support the hypothesis that H. frenatus led to the fragmentation and extinction of the endemic Nactus populations and demonstrate that artificial refugia made of a crumbly substrate may be used to limit future disturbances by this gecko and others like it in the Mascarene Islands and elsewhere.