Ground beetle assemblages in cultivated organic soil and adjacent habitats: temporal dynamics of microspatial changes

Agricultural areas comprise both perennial and annually disturbed habitats. Cultivated habitats are thought to harbor a succession of species that first use the growing field as a passageway then establish themselves as the crop grows. The temporal and spatial changes in carabid assemblages were quantified using pitfall traps set in and around carrots cultivated on organic soil in southwestern Quebec. A total of 76 species of 30 genera were captured. Five species constituted 69% of the captures: Amara littoralis (714 individuals), Anisodactylus sanctaecrucis (915 individuals), Bembidion quadrimaculatum oppositum (1041 individuals), Pterostichus melanarius (1565 individuals) and Stenolophus comma (1088 individuals). A correspondence analysis showed that carabid assemblages were characteristics for the carrot field, the wet ditches, the bare soil and the fallow. A temporal analysis discriminated between spring and fall breeders. The first axis was related to the vegetation cover whilst the second axis was related to moisture gradient. Multivariate analysis confirmed the presence of carabid assemblages based on the described habitats except for bare soil. These assemblages of species are not present early in the season and appear in July and August when the vegetation in the field is abundant. Later in September, October and November, after carrot harvest, these assemblages disappear gradually. Our results support the concept of permeability where species characteristic of a habitat are also captured albeit at a lower rate in adjacent habitats.