Carabid beetle activity-density and diversity in northern hardwood forests of Michigan.

Abstract

Natural habitats can experience many types of anthropogenic alterations such as fragmentation, urban land development, introduction of exotic species, pollution, logging, and changes in fire regimes. These alterations are one of the leading factors influencing the world-wide decline in biodiversity. This dissertation investigates carabid beetles (Coleoptera: Carabidae) in northern hardwood forests of Michigan in relation to habitat factors such as forest type, presence of beech bark disease, thinning, and downed woody debris. In this study, the carabid community changed significantly throughout the summer; carabid species richness peaked in June and abundance was highest in August. Several carabid species were significantly associated with one of the three types of northern hardwood forests that were investigated: maple-beech forests in the Lower Peninsula, oak-beech forests in the Lower Peninsula, and maple-beech forests in the Upper Peninsula. Effects of beech bark disease on carabid beetles were not consistent across study sites. Thinning had a negative impact on carabid activity-density but a positive effect on carabid species richness. I found that amount and decay stage of downed wood was an important factor in determining carabid species composition. Eighty-nine percent of the carabid species were significantly associated with a particular type of downed wood, and wood in the advanced decay stages was particularly important to several carabid species. When I compared the carabid community composition found using three different sampling techniques (two pitfall trap layouts and meander surveys), I found that relative capture rate was clearly dependent on downed wood type for each species collected in pitfalls placed next to downed wood or in meander surveys. Relative abundance of carabid species collected in stands with beech bark disease, thinned stands, and control stands was significantly dependent on the collection method. The results of my study document: (1) the importance of sampling carabid species abundances over the entire season, (2) the need to evaluate even seemingly similar habitats for species differences, (3) the significance of a variety of downed wood types as habitat for carabid beetles, and (4) the need to use multiple sampling techniques to adequately access carabid communities.