Spider (Araneae) populations in hayfields and pastures in northern Iceland

Abstract

Abstract: Surface‐living spiders were collected in pitfall traps over a 1‐year period in three unimproved pastures and three managed hayfields in northern Iceland, located on sandy, silty and peaty soil. On each of the six fields, six pitfall traps were placed and emptied approximately once a week during summer season, but two traps at longer intervals during winter season. During the summer season, the number of spider specimens was significantly higher in sand than in silt, with peat soil in an intermediate position. Annual management of hayfields includes fertilization, hay cutting and occasional grazing. A total of 22 spider species were collected in the pastures and only 17 in the hayfields. However, the total number of specimens was not significantly different between the two. All spider species were more abundant in pastures than hayfields, with the exception of Erigone atra Blackwall, 1883 and Erigone arctica (White, 1852). These two species dominated the hayfields, together composing 79% of the spider population there, followed by Allomengea scopigera (Grube, 1859) with 7%. The dominance of E. atra in hayfields is related to fertile soils and high‐yielding grass species, which might lead to an increase in certain Collembola species which serve as an important feed for this spider species. However, Tenuiphantes mengei (Kulczyński, 1887) dominated the pastures, representing 22% of the spider population, followed by A. scopigera, Pardosa sphagnicola (Dahl, 1908) and E. atra composing 17, 13 and 12% of the spider population, respectively. E. atra had two abundance peaks, a large peak in early spring (3.7 specimens/day in hayfields), and a smaller peak in early summer, while abundance was much lower the rest of the year. Tenuiphantes mengei had two distinct abundance peaks, one in early summer (0.7 specimens/day in pastures) and another in the autumn, while A. scopigera was almost entirely found in the autumn (1.0 specimens/day in pastures). In general, winter abundance was low, 0.2 specimens/day, compared with 4.4 specimens/day in summer season. In early winter, T. mengei dominated (43% of the spider population), while E. atra dominated in mid‐ and late winter composing 47 and 80% of the spider population respectively.