Aims To evaluate the role of native predators (birds) within an Australian foodweb (lerp psyllids and eucalyptus trees) reassembled in California.
Location Eucalyptus groves within Santa Cruz, California.
Methods We compared bird diversity and abundance between a eucalyptus grove infested with lerp psyllids and a grove that was uninfested, using point counts. We documented shifts in the foraging behaviour of birds between the groves using structured behavioural observations. Additionally, we judged the effect of bird foraging on lerp psyllid abundance using exclosure experiments.
Results We found a greater richness and abundance of Californian birds within a psyllid infested eucalyptus grove compared to a matched non-infested grove, and that Californian birds modify their foraging behaviour within the infested grove in order to concentrate on ingesting psyllids. This suggests that Californian birds could provide indirect top-down benefits to eucalyptus trees similar to those observed in Australia. However, using bird exclosure experiments, we found no evidence of top-down control of lerp psyllids by Californian birds.
Main conclusions We suggest that physiological and foraging differences between Californian and Australian pysllid-eating birds account for the failure to observe top-down control of psyllid populations in California. The increasing rate of non-indigenous species invasions has produced local biotas that are almost entirely composed of non-indigenous species. This example illustrates the complex nature of cosmopolitan native-exotic food webs, and the ecological insights obtainable through their study.