Spiders (Araneae) from square samples and pitfall traps in coastal heathland, western Norway. Habitat preference, phenology and distribution

Square samples were taken at intervals of 3 - 4 weeks (early spring 1972 - late summer 1973) in a heterogenous plant association dominated by Calluna vulgaris and several moss species (Loc.I), and in a homogenous, humid Sphagnum mat (Loc.II) with very sparse Calluna. Probably due to an unusually dry spring/early summer in 1972 the density of spiders decreased drastically towards mid-summer at Loc.I, especially the linyphiids and in particular their juveniles (less so at Loc.II). During late autumn/early winter a maximum of approximately 300 and 200 specimens per square meter was reached at Loc I and II, respectively. A total of 43 species were found; at Loc.I 42 species and at Loc. II 29 species. The Shannon indices of general diversity were 2.28 and 1.26, respectively. The sharing of 28 species gave a fairly high Soerensen index of similarity (0.79) but a rather low Renkonen index (0.30). At Loc.I the four most dominant species (range 12 - 21% ), Minyriolus pusillus, Erigonella hiemalis, Gongylidiellum latebricola and G. vivum, represented 59% of the total. At Loc.II the two most dominant species Robertus arundineti (45%) and Minyriolus pusillus (10%) represented 55% of the total. Pitfall traps emptied every 3 - 4 weeks added another 25 species to the list, including some abundant lycosids, and occasional sampling elsewhere in the area added 6 species. Phenological data are presented, and for some abundant species briefly discussed with notes on their habitat preferences and distribution.