The effects of an exotic lizard, Anolis sagrei, on arthropod diversity and ecosystem functioning in betelnut palm plantation in Taiwan

The brown anole, (Anolis sagrei) has been accidentally introduced into Taiwan for about 7 years. Previous studies showed that this lizard tends to have a negative effect on spider and arthropod diversities. In Taiwan, betelnut palm plantationa are suitable habitats for A. sagrei and these lizards have been found in large numbers in such habitats. From 2004 to 2006, we compared a betelnut palm plantation with the lizards present with one where the lizards were removed to quantify the impacts of the invasive lizard on spider and insect diversity. In lizards’ stomach contents, spiders comprised 10 % of the prey consumed and most of which were members of the families Salticidae and Linyphiidae. Insects comprised the other 90 % of the prey, of which the majority were ants, particularly Pheidole fervens. Direct predation by the lizards might have negatively impacted on spider and insect diversities, because the abundance of Salticidae spiders and ants were significantly lower in the betelnut palm plantation with the lizards present. To further confirm such impacts, we manipulated lizard density in enclosures established in the betelnut plantations to determine the effects of manipulating lizard abundance on arthropod diversity and litter decomposition. Direct predation by lizards caused negative effects on abundance of Salticidae and dominant ant species. A substantial reduction in P. fervens ants led to a significant difference in ant community structure. However, since the abundance of predators of collembola such as wolf spiders and Strumigenys ants were not affected by lizards, the litter decomposition rate did not differ between treatments. Results of our study demonstrated that the introduced brown anole has negative effects on arthropod diversity in betelnut palm plantations in Taiwan, but how this lizard impacts ecosystem functioning awaits further study.