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- Bengtson, Sven-Axel, et al.
(author)
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Man-dependence of House Sparrows (Passer domesticus) in the Faroe Islands: habitat patch characteristics as determinants of presence and numbers
- 2010
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In: Dorete - her book, Annales Societatis Scientiarum Færoensis, Suppl. 52. ; , s. 227-243
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Book chapter (other academic/artistic)abstract
- The House Sparrow (Passer domesticus) began to colonize the Faroe Islands in the mid-1940s and occurs in most built-up areas. Breeding is confined to the discrete human habitations (settlements) that form a pattern of patches (”habitat-islands”). In 2002 all settlements were surveyed and the number of pairs of sparrows (total number ca. 2,700 pairs) and amount of vegetation (”green space”) were estimated. The settlements ranged in size from 0.01 km2 (a single farmstead) to 8.72 km2 (the capital) and 68% of them (n=118) were occupied by sparrows. Patch occupancy was positively correlated with both area and amount of vegetation (p < 0.001) but not quite with the degree of isolation (p = 0.15). The latter was crudely scored as a function of distance to nearest settlement with > 10 pairs (a possible source area) and topography (mainly mountains and open sea). The patch variables area, human population, number of houses and houses were strongly intercorrelated. Abundance (number of pairs) of sparrows was positively correlated with the number of houses (r = 0.84, p < 0.001). In all but one of the settlements with < 10 houses sparrows were absent, and also in many of those with 10-60 houses where the scatter swas wide (no significant correlation p = 0.25). All but one of the settlements with > 60 houses supported sparrows and the correlation with abundance was highly significant (p < 0.001). The absence of sparrows in small settlements is discussed in terms of risks of associated with small populations such as stochastic extinctions, Allee effects, competition, and predation (incl. persecution by Man). Various anthropogenic effects on abundance of sparrows are discussed; e.g. age, type and conditions of buildings and the presence of gardens, cultivations, and plantations all contributing to shelter and food resources. The Faroese House Sparrow as a metapopulation is briefly discussed.
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- Bengtson, Sven-Axel, et al.
(author)
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Spiders in Iceland: distributions, species richness, and faunal changes
- 2007
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In: Insect Systematics & Evolution. - 1399-560X. ; 38, s. 97-120
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Journal article (peer-reviewed)abstract
- 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.
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