Effect of habitat type and pitfall trap installation on captures of epigaeic arthropod assemblages in the boreal forest

Abstract

AbstractIt is unrealistic to achieve high-resolution biodiversity inventories required to support local conservation strategies over large areas; however, benchmark associations between arthropods and ecosystem classification can support landscape scale biomonitoring. We investigated habitat associations of ground-dwelling spiders (Araneae), staphylinid beetles (Coleoptera: Staphylinidae), and carabid beetles (Coleoptera: Carabidae) in three forest ecosystems in northwestern Alberta, Canada and also studied the effect of variation in depth of pitfall trap installation on catch. Composition and diversity of all three taxa were correlated with the ecosystem classification map, and 20 species were strong indicators of particular habitats. The black spruce (Picea mariana(Miller) Britton, Sterns, and Poggenburg; Pinaceae) bog supported fewer species and individuals of beetles but this trend was not observed for spiders because of natural history traits associated with their performance in this environment. Pitfall trapping biases were constant among habitats enabling proper comparison of ground-dwelling invertebrate assemblages. Three species of beetles (Agonum retractumLeConte (Coleoptera: Carabidae),Pterostichus brevicornis(Kirby) (Coleoptera: Carabidae), andQuedius veloxSmetana (Coleoptera: Staphylinidae)) were disproportionally active beneath the soil surface, as catches were greater in pitfall traps with the lip situated 15–25 cm below the soil surface. Thus, even highly standardised trap placement will influence the concept of biodiversity achieved through pitfall trapping, because some target organisms are disproportionately active in subterranean zones.