Spiders in Iceland: distributions, species richness, and faunal changes

• Spiders were collected, mostly by pitfall trapping in the 1970s, in a variety of habitats, mainly in lowland areas all around Iceland. Among the 62 species collected five were first records for Iceland (viz. Micaria pulicaria, Robertus lyrifer, Theonoe minutissima, Wabasso replicatus, and Bathyphantes gracilis). Most of the material (comprising ca 18 000 adult spiders) was obtained by pitfall trapping at 54 sites in 1976-1977. Additional methods such as sweep netting, vacuum sampling, sieving, and collecting by hand were employed at some of the pitfall sites and also in ca 250 sites where supplementary collecting was carried out. The pitfall traps were usually operated throughout the summer(June-August) and in many cases all year around. Distribution and seasonal activity of species are described. A total number of 57 species was caught in the pitfall traps but the number varied considerably between sites and habitats, probably to a large extent due to variation in collecting efforts, especially seasonal coverage and sample sizes. Species richness in relation to habitat was assessed by comparing summer samples (i.e. June-August) and applying rarefaction, which showed that mean species number is higher (albeit only slightly so) in the habitats with a more complex vegetational structure (viz. birch woods, plantations and those with shrubs) than the more open habitats (i.e. heaths, grasslands, and meadows). Most of the relatively common species (in terms of abundance and number of sites) occur in a broad spectrum of habitats and have wide geographic distributions in Iceland. About 42 % of the species were found in 1-3 sites only and 16 % in > 50 % of the pitfall sites. Species-abundance distribution was even more unimodal though the positive correlation between number of individuals and sites shows a wide scatter. The apparent rarity of some of the species is discussed and the importance of a sufficienly extended seasonal coverage and to use different collecting methods is recognised and exemplified. A comparison of the results of the present Survey with previously published records, including results from extensive pitfall trapping in the 1990s, Suggests some changes in the spider fauna and several cases of possible, relatively recent immigrations to Iceland are discussed.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

NATURVETENSKAP  -- Biologi -- Zoologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Zoology (hsv//eng)

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