Biodiversity of ground beetles (Coleoptera: Carabidae) and spiders (Araneae) across a tallgrass prairie - aspen forest ecotone in southern Manitoba

The objective of this study was to assess the similarities and differences between selected bioindicator groups within tallgrass prairie and adjacent aspen forest. Based on pitfall trapping from 1998 to 2000, species richness and abundance of ground beetles and spiders were examined across a tallgrass prairie – aspen forest ecotone located near Winnipeg, Manitoba. The abundance of spiders and ground beetles was higher in the forested portion of the transect than in the prairie section. There were 639 specimens of ground beetles collected, representing 53 species; 19 species were found only on the prairie, 19 species were found only in the forest, and 15 species were found in both habitats, although the abundance of most species was too low to confidently assign them to either habitat type. Excluding single records in any sampling year yielded 9 prairie species, 5 forest species, and 10 species found in both aspen forest and tallgrass prairie. The five most abundant species of ground beetles were Agonum placidum (Say), Pterostichus caudicalis (Say), P. femoralis (Kirby), P. melanarius (Illiger), and Synuchus impunctatus (Say). There were 4499 specimens of spiders collected, representing 92 species; 25 species were found only in the prairie, 15 species were unique to the aspen forest, and 52 species were found in both habitats. Excluding single records in any sampling year yielded 26 prairie species, 15 forest species, and 22 species found in both habitats. The five most abundant species of spiders were Pardosa moesta Banks, P. distincta (Blackwall), Agroeca ornata Banks, Centromerus sylvaticus (Blackwall), and Alopecosa aculeata (Clerck). Our study concurs with other studies in demonstrating that there are distinct assemblages of both groups of predators in each of the two habitat types. Le but de notre étude est d'évaluer les ressemblances et les différences entre des groupes choisis de bioindicateurs dans une prairie d'herbes hautes et la forêt adjacente de peupliers. Nous avons déterminé au moyen de récoltes au piège à fosse de 1998 à 2000 la richesse spécifique et l'abondance des carabes et des araignées en travers d'un écotone de prairie à herbes hautes et de forêt de peupliers près de Winnipeg, Manitoba. L'abondance des araignées et des carabes est plus grande dans la partie forestière du transect que dans la prairie. Les récoltes contiennent 639 spécimens de carabes appartenant à 53 espèces; 19 espèces se retrouvent seulement en forêt, 19 seulement e