Distribution, density and habitat association of the Cook Strait click beetle (Amychus granulatus Coleoptera: Elateridae) on Te Pākeka/Maud Island, New Zealand

Abstract

ABSTRACT The Cook Strait click beetle (Amychus granulatus) is found only in five offshore island refugia in New Zealand. We estimated their elevational distribution, population density, and habitat associations within sampling plots on Te Pākeka/Maud Island using mark-recapture methods. We marked and recaptured individual beetles during seven nightly surveys in November 2020 and recorded a range of environmental variables to better understand their habitat associations. Our surveys confirmed the presence of beetles across the island's elevational range, but population densities appeared highest at lower elevations. Based on recaptures, we estimated a mean density of 892 beetles/ha (95% CI: 556–1620) in one large, low-elevation plot and 575 beetles/ha (95% CI: 230–1960) across the remaining plots. Temperature may have affected nightly beetle activity, and hence also capture probability. Habitat assessments suggest the abundance of mahoe (Melicytus ramiflorus), and daytime refugia in tree cavities or rocky areas positively affected beetle counts. Our results provide the first robust population estimates for this endemic species. The apparent patchy distribution pattern we observed and its possible link to environmental variables have the potential to inform on conservation management including future translocations of Cook Strait click beetles to predator-free locations where suitable habitat exists.