A Five-Year Study of the Ground-Dwelling Beetles (Coleoptera) from a Grassland and an Adjacent Woods in Southern Québec (Canada)

We present results of the first long-term study on spatiotemporal variations in the composition and structure of ground-dwelling beetle assemblages from a grassland and adjacent woods in eastern Canada. It is the third part of an investigation on the beetle biodiversity using diverse methods between 2006 and 2012. During the entire snow-free season (April/May to October) in 2006–2010, we collected by pitfall trapping 67694 individuals representing 386 Coleoptera species and morphospecies belonging to 35 families in southern Québec. Adventive species represented at least 51.9% of individuals. Carabidae and Staphylinidae were the most abundant families and had the highest species richness in all seven pitfall trap lines (two lines in a grassland, one line at the edge of the woods, two lines in the woods, and two lines near a ditch parallel to the woods). We did not detect a trend in annual variations of total catches and species richness in each pitfall trap line. A large part of the species (42.2%) occurred as singletons or doubletons over all sampling months. We collected at least 100 individuals for 50 species, including four eudominant species: Tachinus limbatus Melsheimer (14.0% of the total catches), Pterostichus melanarius (Illiger) (10.5%), Drusilla canaliculata (Fabricius) (9.6%) and Anotylus rugosus (Fabricius) (5.3%). Over all sampling years, between 49 and 63% of species from one pitfall trap line were sporadically collected (i.e., during one to three months only over five years), whereas only a few species were active during at least 26 months over all the 33 sampling months in each pitfall trap line. Fourteen species were dominant in at least one pitfall trap line; we observed strong year-to-year fluctuations in the relative abundance of dominant and subdominant species in each line, and spatiotemporal variations of each of these species. We determined the sex-ratio for 42 abundant species, including 17 species with a female biased sex-ratio, and 13 species with a predominance of males. Adults of the most abundant species were mostly macropterous (73% of catches), and we discuss on their dispersal power by flight.