Effectiveness and biases of Winkler litter extraction and pitfall trapping for collecting ground-dwelling ants in northern temperate forests

Abstract

The sampling efficiency of pitfall traps and Winkler litter extraction in northern deciduous forests was compared using ants. Both techniques are among the most common methods used to measure the diversity of organisms active on the forest floor. During 2005-2006, 90 Winkler and 180 pitfall trap samples from urban forest fragments in northeastern Ohio obtained 9,203 ants representing 31 species. Winklers captured all 31 species, whereas pitfall traps collected a total of 24 species. Winkler samples accumulated species more rapidly than did pitfall traps and had greater total species richness and higher abundance of ants recorded. Consistent with other studies, Winkler sampling was found to catch a greater number of smaller ants, whereas pitfall trapping caught a greater number of large-bodied ants. According to estimates of expected species richness, the combination of the two sampling techniques allowed for the collection of approximately 90% of the ants expected in the surveyed area. Site variation had little effect on the inherent differences in sampling efficacy between the two methods. Either technique adequately collected samples for broad comparisons and documentation of the more typical and representative ant fauna, but Winkler extraction exhibited the advantage of a more complete inventory. The application of both techniques should be considered if the aims of a study require estimation of community properties, such as relative abundance.