The influence of pasture management intensity on species richness and abundance of beetles (Coleoptera: Carabidae, Staphylinidae and Curculionoidea) on a managed Nova Scotia pasture

Pastures, about 1/3 of agricultural land in Nova Scotia and Canada, are grassland agroecosystems managed to provide quality forage at minimal cost. Well-managed pastures support diverse biological communities, providing ecological services, such as pest management and nutrient cycling which reduce the need for inputs (e.g. pesticides and fertilizers) while promoting forage quality. Loss of biodiversity in pastures can reduce trophic linkages within the ecosystem, which can reduce ecosystem integrity, requiring greater inputs to maintain pasture quality, thereby increasing producer costs. Pastures in Nova Scotia are human-created open habitats, dominated by non-native plants, differing significantly in structure and disturbance from the natural forest ecosystems of the province. Beetles are abundant and speciose in pastures, occupying many niches, and several taxa are useful indicators of environmental disturbance and overall system biodiversity. In this study, I assessed biodiversity of common beetle taxa (Carabidae, Staphylinidae, Curculionoidea) at different management intensities to determine the effect of management intensity on beetle diversity. Beetles were sampled from an experimental dairy pasture in Nova Scotia, which had been divided into eight replicates of four management treatments varying in frequency of grazing, clipping and harrowing. Beetles were collected over four sampling periods through the summer of 2007 using a combination of pitfall traps and sweep transects. Pitfalls were deployed in a grid of 96 traps over 2268 trap-nights and 256 sweeps were conducted along 20 sweep, 20 m transects. Eighty-five species and 2,436 individuals - 15 species of Carabidae (n = 841), 40 species of Staphylinidae (n = 704) and 30 species of Curculionoidea (n = 886; 28 Curculionidae, n = 719; 2 Brentidae, n = 172) were collected. Total species richness of these taxa was estimated at 112-116 species, meaning ∼75% have been recorded. Species richness was greatest in the Semi-Intensive treatment, with management similar to standard pasture practices in Nova Scotia, though abundance was low. Abundance was greatest in the least intensively managed treatments, primarily due to high abundance of a few species of seed-eating ground beetles. Species richness of carnivores was greatest under Semi-Intensive management, while phytophagous species richness was greatest under Intensive management and omnivore species richness did not differ among the treatments. Carnivore species abundance did not differ among the treatments, while phytophagous and omnivorous species were more abundant under low-intensity management, likely due to higher volume of plant biomass, especially seed heads. Fifty-nine percent of species and 85% of individuals collected were of non-native origin; abundance of native species was low, and did not differ among the treatments. In contrast, non-native taxa primarily accounted for the trends of species richness and abundance seen with all species combined. No species were indicators of management intensity though species level abundance patterns showed association with different levels of management. Four first records for the province of Nova Scotia were collected, all of which were Staphylinidae: Oxypoda perexilis Casey, Illyobates bennetti Donistorphe, Atheta platanof Brundin, and Stenus arculus Erichson. More intensive pasture management is not detrimental to pasture beetle diversity in Nova Scotia.