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Effects of habitat structure and lid transparency on pitfall catches

Phillips, I.D., Cobb, T.P.
Environmental entomology 2005 v.34 no.4 pp. 875-882
Carabidae, trapping, pitfall traps, equipment performance, habitats, environmental factors, microclimate, soil temperature, insect behavior, sampling, species diversity, boreal forests
We present a methodological study that aims to help placate some of the criticism surrounding the use of pitfall trapping for carabid beetles in ecological studies. Because pitfall trap catches are dependent on the activity of carabids and not solely on density, characteristics of the trap construction may influence the success of the trap in different habitat types. Specifically, traditional opaque wooden lids may change the temperature and sun exposure of a trap relative to its surroundings. These abiotic factors may vary with the vegetation structure present around the trap. Thus, traditional opaque lids may offer a shade refuge in low vegetation habitats. We hypothesized that a change in microclimate associated with lid transparency would alter the behavior of ground beetles and thereby lead to a bias in trap catch results. To test this hypothesis, we performed a replicated, two-factor experiment manipulating lid transparency (opaque, partially transparent, and completely transparent) and vegetation height (>2, 1, <0.5 m) around 27 pitfall traps. Soil temperatures beneath each lid varied significantly with lid transparency and vegetation height. There was no effect of either treatment on carabid species richness, whereas species assemblages varied significantly with respect to vegetation height but not lid transparency. However, total carabid catch rates and overall carabid species composition varied significantly with vegetation height but not lid transparency. Therefore, our results show that lid transparency does not bias carabid beetle catch and lend support to the use of pitfall trapping to assess the effects of habitat change on epigaeic communities.