The distribution and habitat characteristics of a threatened lucanid beetle Hoplogonus simsoni in north-east Tasmania

Abstract

The distribution and characteristics of habitat utilized by a threatened species of stag beetle in north-east Tasmania Hoplogonus simsoni (Coleoptera: Lucanidae), were examined as a first step in the development of conservation management objectives for the species. The beetle was found to have a restricted distribution of 250 km2 and its regional distribution appeared to be related to the occurrence of granitic geology and a moderately high rainfall at low elevations. The species was patchily distributed across its range. High-density populations of the species were restricted to the eastern part of its distribution, but over most of its range it occurred at very low densities. Relative abundances of H. simsoni were greatest in wet eucalypt forest, with significantly fewer beetles found in mixed forest and rainforest. Dry eucalypt forest was found to be unsuitaole habitat although the beetle was found to occur in the ecotone between wet and dry eucalypt forest Potential wet forest habitat for the species is estimated to encompass 18 200 ha or 72% of its range. The species was not found in areas of wet eucalypt forest that had been converted to pine plantation. However, H. simsoni was found to occur in wet eucalypt forest regenerating after clearfelling and some of the highest density populations of the species occurred in 70 year old wet eucalypt forest regenerating following a wildfire. The relationship between various habitat variables and the occurrence of the beetle was investigated using Generalized Additive Modelling and robust regression. The presence of wet eucalypt forest below 300 m altitude; slope less than 5°; a deep leaf litter layer; and a forest structure with a well-developed canopy best explained the occurrence of the beetle. These habitat characteristics probably relate to a requirement for a cool, moist, stable microclimate and an absence of wildfire for some time. The potential habitat of H. simsoni as identified in this study is poorly reserved across its range and a high percentage has been identified by the forest industry as having potential for conversion to pine plantation. This highlights the importance of having mechanisms for "off-reserve" conservation of threatened species. like H. simsoni, which are often poorly represented in or completely absent from formal reserves.