The effects of Anolis sagrei, an exotic lizard, on arthropod diversity and ecosystem functioning in a betelnut plantation in southern Taiwan.
(Chapter 1) Predation effects could be achieved by directly reducing prey abundance and by indirectly via altering behavioral patterns of prey. In the past, there was little evidence that ant community structure composition could be affected by vertebrate predations. Researchers tend to consider the interactions between vertebrate predators and ants to be weak. In this study, we examined the impacts of the exotic invasive lizard, Anolis sagrei, on ant community structure by manipulating the density of lizards by enclosures. The natural density of A. sagrei in the field was surveyed and used as the density in the lizard-present subenclosures. Before lizard density was manipulated, there was no difference in ant diversity between subenclosures. After lizard density manipulation the ant diversity in subenclosures with A. sagrei present was significantly different from that of enclosures without, although overall ant abundance did not differ significantly. The ant diversity difference was generated by abundance change of ant species Pheidole fervens due to predation pressure of A. sagrei. A significantly lower P. fervens in subenclosures with A. sagrei present might result from direct predation of lizards, or was generated by foraging site shift of this ant. Results of this study thus demonstrated that the invasion of an exotic vertebrate could significantly alter the community structure of ants via predation.
(Chapter 2) Litter decomposition rate is an important factor affecting nutrient recycling in the detritus ecosystem. Collembola are among the most abundant micro-detritivores in leaf litter and play the key roles in the functioning. Collembola influence the litter decomposition rate directly by feeding on litters and indirectly by consuming the fungi involved in the detritus recycling process. Ground spiders such as the family Lycosidae is the major predator of collembola and some genera of ants also take collembola as major prey resource. In this study, we established enclosures to manipulate the density of an invasive lizard, Anolis sagrei, to determine whether the introduction of this lizard would indirectly affect collembola abundance and diversity by predating their predators such as ants and spiders, and consequently affecting litter decomposition rate. We surveyed the natural density of A. sagrei and used that as the density in lizard-present subenclosures. After the manipulation, the overall ant abundance did not differ between two lizard-present and lizard-removed subenclosures. The abundance of Strumigenys ant, the collembola specialist, was very low, so its impact on collembola could not be assessed. After lizard density manipulation although the abundance of jumping spiders (Salticidae) differed significantly, that of the major spider predator of collembola, the wolf spider (Lycosidae), showed no significant change. Neither abundance nor diversity of collembola differed significantly between two types of subenclosures. Congruent with such results were the litter decomposition rates, which also showed no significant differences. Results of this study showed that although presence of the invasive A. sagrei altered ant community structure, this lizard did not significantly affect major predators of collembola and thus collembola abundance and consequently litter decomposition was not impacted.
Updated: Mar-10-2014 01:22:51 (Taiwan, GMT+08:00).