Are exotic invaders less susceptible to native predators? A test using native and exotic mosquito species in New Zealand

摘要

A major hypothesis in invasion ecology is that native predators have less impact on exotic relative to native prey species. Here, we tested this hypothesis by examining the New Zealand native predator Anisops wakefieldi consuming native (Culex pervigilans) and exotic (Aedes notoscriptus) mosquito larvae. Anisops wakefieldi exhibited a decelerating type II functional response for both prey species, but at high prey densities consumed more of the exotic mosquito Ae. notoscriptus. A significantly higher attack rate was observed for the native predator feeding on exotic species. In the presence of both prey species, the predator showed preferences towards Ae. notoscriptus and demonstrated switching behavior towards this exotic species. The preference of the native predator towards the exotic mosquito appeared related to behavioral differences between the two prey species. We tested the behavioral response of both mosquito species in four conditions; (1) control (without predators), (2) free-roaming predators, (3) caged predators, and (4) kairomones only. Resting activities at the water surface and wall positions were the most frequently behaviors exhibited by Cx. pervigilans in the presence of predator. In contrast, the exotic species Ae. notoscriptus demonstrated significantly higher levels of “thrashing” behaviors, apparently making itself more obvious to the predators. The behaviors showed by Cx. pervigilans fulfilled the “threat sensitivity hypothesis”. No evidence here supported the idea that exotic mosquito species are less prone to the influence of native predators and the “escape from natural enemies” hypothesis seems not apply in our study. In fact, we observed that this invader was more susceptible to the predator.