Sampling dung beetles in the French Mediterranean area: effects of abiotic factors and farm practices

1. The confidence limits and the validity of the results obtained by using dungbaited traps were examined in five sites in southern France, which were very close together and similar for most environmental variables but differed in their pastoral history. Site 1 was a virgin site which had been grazed for only a few months by cattle; site 2 had been grazed for 10 years by cattle but the cattle herd had been removed in the previous year; the other three sites had been grazed by sheep, more or less extensively, for many years. 2. Beetle abundance, biomass or richness were not correlated with temperature and precipitation, but were significantly correlated with radiant energy. The energy necessary for flight activity was probably related to the radiant energy level at the soil surface. This allowed identification of the most favourable periods for sampling. 3. At the sites with at present limited resources, the mean biomass of trapped beetles decreased rapidly when repetitive trappings were carried out over several days. An intense trapping during a continuous period led to an underestimate of the number of beetles, due to site impoverishment. When the cattle herd was removed and dung was therefore not available, the trappings made a few months later overestimated the number of beetles. In contrast, after the establishment of a new, large cattle herd in a virgin site, formerly free of grazing, the baited traps underestimated the number of beetles, due to the amount of dung present in the vicinity of the traps. 4. One trapping session and five traps collected 75-80 % of total local species but 95 % of the abundance and biomass of the community. So, for most of the ecological studies, one trapping session and a few baited traps (five in the Mediterranean area where dung beetle communities are very diverse when compared with more temperate areas) are sufficient to give a sample representing the structure of the dung beetle communities. Conversely, an exhaustive inventory for biogeographical studies need more baited traps. At least 15 traps are necessary to collect 95 % of species present at a site. An abacus allows an estimate of the quality of the sampling.