Contrasting patterns of habitat use in a threatened carabid (Carabus intricatus) and a sympatric congener in ancient temperate rainforest

Abstract

There is increasing concern into the decline of insect populations, with corresponding calls for conservation action aimed towards threatened species in particular. However, there is a distinct paucity of knowledge surrounding habitat requirements, microhabitat selection and conservation actions that may be undertaken for the vast majority of invertebrate species. Carabus intricatus (Coleoptera: Carabidae) Linnaeus, 1761 is a threatened ancient woodland specialist in the United Kingdom with a highly restricted distribution and is listed as a section 41 species of principal importance in England. Despite this, no empirical systematic evidence exists for even basic habitat requirements. Here, we used a patch‐occupancy modelling framework to determine occupancy and detection parameters for C. intricatus and a sympatric generalist species, C. problematicus, which is a potential competitor. Our models showed that decayed deadwood availability and leaf litter covering (an indicator of the availability of mature broadleaved trees) leads to higher occupancy of C. intricatus, whereas decayed dead wood availability and slug abundance are primary determinants of overall abundance. Additionally, detection models showed that higher humidity substantially increased activity of C. intricatus. For C. problematicus, ground moss coverage and overall deadwood volume most strongly influenced occupancy and abundance, whereas there were no humidity related influences on activity. The results support our general predictions about the specialist–generalist nature of the two species in the United Kingdom and indicate that key characteristics of old‐growth temperate rain forests, particularly the availability of deadwood and high humidity, are central to the conservation of these charismatic carabids.