Jaime Pinzon

Bark-dwelling spider assemblages (Araneae) in the boreal forest: dominance, diversity, composition and life-histories

We collected spiders from tree-bark, foliage and litter habitats in deciduous and conifer dominated stands in NW Alberta (Canada) to define these assemblages and consider their conservation significance. To establish habitat associations, we used Indicator Species Analysis (ISA) together with a species dominance metric (DV′) newly proposed here. Of the 116 species collected, 78 were collected from bark. Results support categorizing 16 species as true bark-dwellers, 16 as facultative bark-dwellers and 46 as accidental bark-dwellers or species of unknown association. Species that were strong indicators of particular microhabitats in analyses restricted to bark habitats lost their indicator value when foliage and ground habitats were also considered, suggesting that bark habitats are critical for specific life-history functions. Clubiona canadensis Emerton 1980, Callobius nomeus (Chamberlin 1919), Pocadicnemis americana Millidge 1976 and Enoplognatha intrepida (Sørensen 1888) were the most common bark-dwelling species but their dominance varied among forest cover-types and trapping techniques. Collecting period, forest cover-type, habitat, and trapping technique were generally important environmental variables influencing composition of bark-dwelling assemblages. Although less important in structuring assemblages, tree status (dead or alive) and decay class were important for particular species. Bark habitats are crucial for boreal forest spider assemblages and must be considered central to maintenance of spider diversity.

Spider Assemblages in the Overstory, Understory, and Ground Layers of Managed Stands in the Western Boreal Mixedwood Forest of Canada

ABSTRACT Logging is the main human disturbance in the boreal forest; thus, understanding the effects of harvesting practices on biodiversity is essential for a more sustainable forestry. To assess changes in spider composition because of harvesting, samples were collected from three forest layers (overstory, understory, and ground) of deciduous and conifer dominated stands in the northwestern Canadian boreal mixedwood forest. Spider assemblages and feeding guild composition were compared between uncut controls and stands harvested to 20% retention. In total, 143 spider species were collected, 74 from the ground, 60 from the understory, and 71 from the overstory, and species composition of these three pools differed considerably among layers. Distinctive spider assemblages were collected from the canopy of each forest cover type but these were only slightly affected by harvesting. However, logging had a greater impact on the species composition in the understory and ground layers when compared with unharvested controls. Guild structure differed among layers, with wandering and sheet-weaving spiders dominant on the ground while orb-weaving and ambush spiders were better represented in the understory and overstory, respectively. Given the ecological importance of spiders and the expectation of faunal changes with increased harvesting, further efforts toward the understanding of species composition in higher strata of the boreal forest are needed.

Performance of two arboreal pitfall trap designs in sampling cursorial spiders from tree trunks

Abstract Tree trunks link the forest floor and higher canopy layers, thus constituting an important habitat element for many arthropod species, including spiders living in the canopy. We sampled spiders moving on tree trunks in the boreal forest using two trap designs referred to as “bottle traps” (BT) and “cup traps” (CT) placed on both trembling aspen (Populus tremuloides Michaux) and white spruce (Picea glauca (Moench) Voss) trees of similar DBH (diameter at breast height). Over an average of 83.5 ± 6.3 days/trap (48 traps), we collected a total 333 spiders, representing 13 families and 33 species. Clubiona canadensis Emerton 1890 (Clubionidae), Callobius bennetti (Blackwall 1846) (Amaurobiidae), Pocadicnemis americana Millidge 1976 (Linyphiidae), and Orodrassus canadensis Platnick & Shadab 1975 (Gnaphosidae) were the most commonly collected species, representing more than 60% of the total catch. Twenty eight species and 285 individuals were collected by BTs compared to 18 species and 48 individuals by CTs. Catches in BTs included 15 unique species, whereas five species were unique in CT catches. BTs are easier to transport and deploy, they catch more spiders per trap, and appear to more efficiently sample spider diversity. Thus we recommend the use of BTs to effectively sample wandering spiders on tree trunks; however, the use of both designs could increase understanding about the role of tree trunks as structural features linking forest canopies to the ground layers below.