Influence of the Invasive Herb Garlic Mustard (Alliaria petiolata) on Ground Beetle (Coleoptera: Carabidae) Assemblages

Abstract

Garlic mustard, Alliaria petiolata (Bieb.) Cavara and Grande, is a widespread invader that has aggressively colonized woodland edges and forest interiors across North America, yet its ecological impacts remain scantily documented. We evaluated the effects of garlic mustard on ground beetle (Coleoptera: Carabidae) assemblages and their invertebrate prey by comparing carabid captures and species richness and invertebrate abundance in invaded and noninvaded areas of two forests in central New York. Geostatistical techniques were used to model ground beetle distribution and to determine spatial correlation between carabids, garlic mustard, ground beetle prey availability, understory plant species richness, and litter depth. Data were collected from April to September 2002, using a grid of 64 by 64 m, with 89 sampling points arranged in nested grids to capture the spatial correlation within and between each variable. Garlic mustard invasion had no effect on carabid captures and species richness or on invertebrate abundance. Ground beetle abundance and biomass were spatially correlated, but their distribution was independent of garlic mustard and all other environmental factors we recorded. Our data on carabid assemblages and their invertebrate prey clearly show that absence or presence of garlic mustard did not influence these organisms at our study sites. It is possible that garlic mustard invasion has negative ecosystem impacts; however, the biennial nature of the plant and its pattern of spread may produce subtle ecological effects that are difficult to quantify or are easily confounded by other dominating factors.