Distribution, habitat associations, and activity patterns of two endemic Banks Peninsula carabid beetles, Mecodema howitti and Megadromus guerinii

Abstract

The distribution and ecology of the potentially threatened forest carabid Mecodema howitti Castelnau and the sympatric but more common Megadromus guerinii (Chaudoir) were studied on Banks Peninsula, Canterbury, New Zealand. Native forest remnants and areas with podocarp/hardwood logs on pasture were surveyed to determine the present distribution range of both species. Their present distribution was compared with their past distribution, as determined from museum collection records, for evidence of range contraction. Environmental characteristics and land use practices were assessed in relation to the presence of each species at the surveyed sites. The spatial pattern, habitat associations, and activity patterns of beetles of each species were investigated by a pitfall trapping and mark-recapture study in a montane podocarp/hardwood forest remnant.

Both species were found in only two of the three ecological districts on Banks Peninsula: Herbert and Akaroa. Museum records and anecdotal reports indicated M. howitti had originally also been present in the Port Hills district. Mecodema howitti had a restricted distribution, and was primarily found in reserved forest remnants and inland areas with podocarp/hardwood logs on pasture in the central and eastern parts of the Peninsula. This species showed positive associations with log abundance and ground-level vegetation density. At the montane study site, M. howitti beetle presence was associated only with log presence. Megadromus guerinii, in contrast, was found throughout the two districts with the exception of the northernmost coastal sites in the Herbert district. At the montane study site, M. guerinii beetles showed an aggregated spatial pattern, partly due to positive associations with the proportion of gravel in the substrate and position on the ridge. Both species were reproductively active in spring and summer. There was some evidence that beetle ecdysis occurs in autumn. The activity patterns of both species were related with temperature and environmental moisture levels. Incidental observations of predation, life cycle stages, prey items, and mite associations are reported. Mecodema howitti was confirmed to be a threatened species. Factors influencing the present distribution of M. howitti are discussed. Recommendations are made for further research and conservation management for this endemic carabid.