Beetles (Coleoptera) as indicators of ecological restoration: a study of revegetated habitats on Matiu-Somes Island, Wellington, New Zealand

Abstract

A study of beetle communities was conducted in three revegetated sites of different ages and in a remnant coastal area dominated by Muehlenbeckia complexa on Matiu-Somes Island, Wellington,New Zealand. Matiu-Somes Island has a long history of human occupation that has resulted in extensive modification of the island's flora and fauna. The study was conducted using pitfall traps (May 1997 to April 1998) and malaise traps (December 1997). A total of 3430 adult beetles from 78 species were caught in pitfall traps, while malaise traps caught 1364 beetles from 30 species. It was concluded that malaise and pitfall traps gave a wide coverage of the beetle taxa in the habitats studied. To collect the largest numbers of specimens, malaise traps are recommended, while pitfall traps are useful for collecting a larger number of species. However, windy conditions during the sampling period lowered the efficiency of malaise traps. Unless investigating beetle seasonality, it is suggested that pitfall trapping is more efficient over a short time period (i.e. 1-3 months) during the peak of insect activity (in December). Most beetles were active for the majority of the year, with abundance peaks during spring and summer (October to February). The temporal distributions of several species were positively correlated with temperature but not with rainfall. Revegetation is successfully facilitating the establishment and recolonisation of the beetle fauna on Matiu-Somes Island. Environmental factors influencing the distribution of beetles in successional habitats were investigated using the ordination programme CANOCO. The most important factors identified were canopy height and canopy density (functions of vegetation age). Overall, results suggest that as habitat/vegetational heterogeneity increases at a site, beetle diversity and abundance increases. Thus, the more mature a replanted site, the greater the species richness and abundance of beetles. In spite of the small area (25 ha) of Matiu-Somes Island and its extensive modification in the past, relatively high numbers of native beetle species were caught. Of 78 beetle species caught in pitfall traps: 66 were classified as native species, and 8 as introduced species. A positive trend was found between the proportions of ground-dwelling native beetle species collected and native plant species present at a study site.