Effects of Cattle on the Abundance and Composition of Carabid Beetles in Temperate Grasslands

Abstract

Grasslands are of vital importance to the ranching industry. Cattle grazing can alter the structure and composition of the plant community, and may indirectly affect insect communities. We investigated the effects of cattle grazing and site productivity on carabid beetle abundance, dried weight (biomass), species richness and diversity. We used pitfall traps to capture beetles in three sessions in 2008 in Lac Du Bois Provincial Park, British Columbia (B.C.), Canada. To test for main and interacting effects of elevation and grazing, carabid beetles were quantified by trap for abundance, dried weight (biomass), species richness and Shannon’s diversity. We found that elevation (a proxy of site productivity) was the most important predictor of carabid parameters, with lower elevation (low site productivity) having lower abundance, biomass, species richness and diversity compared to upper elevation (high site productivity). Although there was no main effect caused by grazing, there was a reduction in carabid biomass and diversity at grazed upper elevation sites compared to ungrazed upper elevation sites, suggesting that site productivity and plant structure affects carabid communities. Cattle management of natural grasslands benefits by considering biodiversity of all biota, including invertebrates. Carabid species diversity can be maximized by restricting grazing at high site productivity where plant biomass and litter is high.