The digging-in effect on ant studies with pitfall traps: influence of type of habitat and sampling time

Pitfall traps are among the most common sampling methods used for the study of ants. There are many types of traps and many possible ways of using them. The various methodologies may introduce biases in sampling. One possible bias may be caused by the digging-in effect (DE), resulting in higher catches of ants immediately after traps are set in the ground which subsequently decline. In this study, we performed two experiments to verify the consequences of the DE for ants in a Mediterranean ecosystem. In the first experiment we distinguished between two types of habitats: closed and open (i.e., with or without shrub or tree cover). The second experiment was carried out in a homogeneous pasture where the time of prevalence of the DE was verified, investigating the duration of the effect. The results indicate differences between communities in the first 24 h after setting of the traps, which had disappeared after 48 h. This does not dismiss the possibility of certain species being affected either positively (increase in captures) or negatively (decrease). Changes in species composition, determining whether the DE was manifested or not, differed among habitat types.