Habitat associations and detectability of the endemic Te Paki ground beetle Mecodema tenaki (Coleoptera: Carabidae)

Te Paki Ecological District in Northland is regarded as a New Zealand biodiversity hotspot, but habitat loss and forest fragmentation have adversely affected many of its endemic species. We investigated the distribution and habitat associations of Mecodema tenaki (Coleoptera: Carabidae), a Te Paki endemic ground beetle whose threat status was recently changed from ‘Nationally Critical’ to ‘Declining’. Manual searching and pitfall trapping (live-capture and lethal) were used to detect the species at 46 sites in three habitat types: native forest, pine plantation and shrubland. Between 2006 and 2010, 41 individuals were found at five locations in the east of the district, significantly increasing individual and locality records for the species. Efficacy of both forms of pitfall trapping for determining presence/absence of M. tenaki was extremely high, whereas manual searching had lower sensitivity. Beetles were only found in structurally heterogeneous native forest with a closed canopy, including edge zones. All beetles were found at sites underlain by rocks of the Parengarenga Group (mainly Kaurahoupo Conglomerate); however, neither forest community composition nor soil properties were good predictors of beetle presence. The most important factor influencing the present distribution of M. tenaki is likely to have been anthropogenic habitat disturbance. Our study shows that lethal trapping methods are not essential for studying or monitoring this threatened species. It also shows that retaining and managing even very small native forest fragments within its historical range may be important for the protection of the species, and that a site-based rather than a single-species approach is likely to be the most effective management strategy. The possibility of relocating beetles to suitable, presently unoccupied locations should not be discounted. Our results indicate that a threat ranking of ‘Nationally Vulnerable’ rather than ‘Declining’ may be more appropriate for the species.