Wary invaders and clever natives: sympatric house geckos show disparate responses to predator scent

The ability to detect and avoid potential predators can enhance fitness, but also has costs, and thus many animals respond to potential predators either in a general (avoid all potential predators) or threat-sensitive (selectively avoid dangerous predators) manner. We used 2-choice trials to investigate strategies used by globally invasive house geckos (Hemidactylus frenatus) and native Australian house geckos (Gehyra dubia) to avoid chemical cues from potential snake predators (Acanthophis antarcticus, Antaresia maculosa, Boiga irregularis, and Pseudechis colletti). Invasive geckos did not respond to a novel chemical cue (perfume), but significantly avoided shelters scented by all 4 predatory snake species, and did not discriminate among snake species that occurred within or outside their current geographic range. Thus, the invasive gecko showed generalized predator avoidance. In contrast, native geckos avoided shelters scented with perfume but did not avoid shelters scented by any of the 4 predatory snake species. We interpret the lack of response by native geckos as threat sensitive, suggesting that they may require additional cues beyond scent alone (e.g., visual cues) to judge the situation as threatening. Generalized responses may be costly for native species living in native habitats filled with predators but may facilitate the rapid establishment of invasive species in novel (especially urban) environments, where general responses to predators may have relatively low costs and enhance survival.