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Sökning: WFRF:(Bengtson Sven Axel)

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1.
  • Bengtson, Sven-Axel, et al. (författare)
  • Man-dependence of House Sparrows (Passer domesticus) in the Faroe Islands: habitat patch characteristics as determinants of presence and numbers
  • 2010
  • Ingår i: Dorete - her book, Annales Societatis Scientiarum Færoensis, Suppl. 52. ; , s. 227-243
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)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 (författare)
  • Araschnia-studier i Norrtou.
  • 2003
  • Ingår i: Fazett. - 1100-2425. ; 16, s. 22-31
  • Tidskriftsartikel (refereegranskat)
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  • Bengtson, Sven-Axel, et al. (författare)
  • Spiders in Iceland: distributions, species richness, and faunal changes
  • 2007
  • Ingår i: Insect Systematics & Evolution. - 1399-560X. ; 38, s. 97-120
  • Tidskriftsartikel (refereegranskat)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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  • Bengtson, Sven-Axel, et al. (författare)
  • Zoologiska museet
  • 2002
  • Ingår i: Mellan liv och död. - 9188846253 ; , s. 185-196
  • Bokkapitel (populärvet., debatt m.m.)
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  • Björn, Lars Olof, et al. (författare)
  • Thermal emissivity of avian eggshells
  • 2016
  • Ingår i: Journal of Thermal Biology. - : Elsevier BV. - 0306-4565 .- 1879-0992. ; 57, s. 1-5
  • Tidskriftsartikel (refereegranskat)abstract
    • The hypothesis has been tested that evolution has resulted in lower thermal emissivity of eggs of birds breeding openly in cold climates than of eggs of birds that nest under protective covering or in warmer climates. Directional thermal emissivity has been estimated from directional–hemispherical reflectance spectra. Due to several methodological difficulties the absolute emissivity is not accurately determined, but differences between species are obvious. Mostnotably, small waders of the genus Calidris, breeding in cold climates on the tundra, and in most cases with uniparental nest attendance, have low directional emissivity of their eggshells, about 0.92 when integration is carried out for wavelengths up to 16 μm. Species belonging to Galloanserinae have the highest directional emissivity, about 0.96, of their eggs. No differences due to climate or breeding conditions were found within this group. Eggs of most other birds tested possess intermediate emissivity, but the values for Pica pica and Corvus corone cornix are as low as for Calidris. Large species-dependent differences in spectral reflectance were found at specific wavelengths. For instance, at 4.259 μm the directional–hemispherical reflectance for galliforms range from 0.05 to 0.09, while for Fratercula arctica and Fulmarus glacialis it is about 0.3.The reflection peaks at 6.5 and 11.3 μm due to calcite are differentially attenuated in differents pecies. In conclusion, the hypothesis that evolution has resulted in lower thermal emissivity of bird-eggs being exposed in cold climates is not supported by our results.The emissivity is not clearly related to nesting habits or climate, and it is unlikely that the small differences observed are ecologically important. The spectral differences between eggs that nevertheless exist should be taken into account when using infrared thermometers for estimating the surface temperature of avian eggs.
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