Krushelnycky, P.D. & Gillespie, R.G. (2010) Sampling across space and time to validate natural experiments: an example with ant invasions in Hawaii. Biological invasions, 12, 643–655.
Studying the ecological impacts of invasive species on an ecosystem can be difficult because experimental approaches involving introduction or removal of an invasive species cannot be used. Instead, such studies are often done by comparing communities of invaded habitats to communities of similar, uninvaded habitats. Krushelnycky and Gillespie test a comparative method of sampling inside and outside of invasion boundaries as well as across time with invasive ant species in two sites on Hawaii Island.
Invaded plots, uninvaded plots, and plots that were expected to become invaded were sampled at each site, examining arthopod species richness and the presence of indicator species associated with invaded and uninvaded conditions. The plots were sampled a second time two years later and community composition was compared between plots and between the two sampling events.
In one site, the community composition in plots before invasion was significantly different from that of invaded plots and not significantly different from uninvaded plots and became significantly different from uninvaded plots and not significantly different from invaded plots after invasion. In the other site, changes in community composition were found in plots before and after invasion. In both sites, several arthropod species that were found to be indicator species shifted in abundance before and after invasion. The results suggested that at least partial transition of community composition had occurred after two years in response to ant invasion.
Significance for Palau:
The two species of ants studied, Phelidole megacephala and Linepithema humile, are reported to be among the most dominant invasive ants in the world. Introduction of these or similar ant species may be a possible threat to Palauan biodiversity, based on their invasion of sites in Hawaii. The small size of some habitats in Palau and the exclusive range of many invertebrate species may further increase the impact of invading species on local communities. The sampling method used in this study may be useful for long term studies in Palau; the authors were able to use this method on another small tropical Pacific island. The study also suggested that more than two years would be needed for significant changes in response to invasion to be observed. Even if differences exist between the conditions described in the paper and Palau, conservation studies in Palau would likely involve similar procedures and comparisons of arthropod and invertebrate communities.