Diversity of forest upland arachnid communities in Manitoba Taiga (Araneae, Opiliones)

Abstract

The diversity of taiga upland arachnid communities, collected mainly in pitfall or pan traps, is compared among forested habitats in two Manitoba regions, one southern and one northern. In the south, where collections were taken both in summer and in winter under the snow cover, the dominant spider families were Erigonidae, Linyphiidae, Lycosidae, and Gnaphosidae. The diurnal and nocturnal pursuit guilds dominated across habitats. In the north, with summer collecting only, dominant familes were Lycosidae, Gnaphosidae and Erigonidae of the diurnal pursuit guild. The southern taiga uplands had 99 species of spiders, northern uplands 49 species with 19 species common to both regions. The five most dominant species from these families are Agroeca ornata Banks, Gnaphosa microps Holm, Pardosa xerampelina (Keyserling), P. mackenziana (Keyserling), and Agelenopsis utahana (Chamberlin and Ivie). Three opilionid species occur in the south and one species, Odiellus pictus Wood, occurs in both regions. In this region of the taiga, we found the most species-rich habitats to be undisturbed forest types, i.e., alder-tamarack ecotone in winter, which produced 34 winter-active species (n=233), with 27 species collected only during winter months. Among-habitat differences in species richness, species dominance and guild composition suggests that maintenance of habitat heterogeneity is needed at all scales to preserve the diversity of forest floor arachnid communities in managed taiga forests.