Relative Efficiency of Pitfall vs. Bait Trapping for Capturing Taxonomic and Functional Diversities of Ant Assemblages in Temperate Heathlands

SIMPLE SUMMARY: Ants, due to their high ecological diversity, are challenging to properly sample. This issue has been addressed by many authors devising multiple sampling techniques. Depending on the habitats sampled, the effectiveness and complementarity of the sampling techniques may vary. Only little work has been done in open temperate habitats. This study aimed to assess the relative efficiency of two common sampling methods: pitfall and bait trapping. The comparison was performed using both a taxonomic (species count) and a functional (i.e., acknowledging of ecological characteristics of species to describe an assemblage of species) approach. Pitfall traps captured more species and a wider set of functional traits than did bait traps, and all species caught by bait traps were also caught by pitfall traps. It therefore appears that in the particular context of open temperate habitats, using bait traps on top of pitfall traps will cost time without information gained and that pitfalls should thus be favored in this context. ABSTRACT: Whereas bait and pitfall trappings are two of the most commonly used techniques for sampling ant assemblages, they have not been properly compared in temperate open habitats. In this study, taking advantage of a large-scale project of heathland restoration (three sites along the French Atlantic Coast forming a north-south gradient), we evaluated the relative efficiency of these two methods for assessing both taxonomic and functional diversities of ants. Ants were collected and identified to species level, and six traits related to morphology, behavior (diet, dispersal and maximum foraging distance), and social life (colony size and dominance type) were attributed to all 23 species. Both observed and estimated species richness were significantly higher in pitfalls compared to spatially pair-matched bait traps. Functional richness followed the same pattern, with consistent results for both community weighted mean (CWM) and Rao’s quadratic entropy. Taxonomic and functional diversities from pitfall assemblages increased from north to south locations, following a pattern frequently reported at larger spatial scales. Bait trapping can hardly be considered a complementary method to pitfall trapping for sampling ants in open temperate habitats, as it appears basically redundant with the latter sampling method, at least in coastal heathlands of the East-Atlantic coast.