| 1. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Patterns of lake acidity and waterfowl communities
- 1994
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Ingår i: Hydrobiologia. - 0018-8158 .- 1573-5117. - 0018-8158 ; 279-280:1, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- Breeding waterfowl communities were studied in 28 lakes in three areas in North Europe, along gradients of acid precipitation and alkalinity that result in lake conditions ranging from unaffected to strongly acidified. Acidic lakes had generally sparser and less complex vegetation, and fewer invertebrates were caught in activity traps. There was neither correlation between pH and waterfowl species richness (genus Anas, family Anatidae, and waterfowl sensu latu tested separately), nor between pH and waterfowl diversity (Simpson's index). Further, pH and waterfowl population density (genus Anas, family Anatidae, and waterfowl sensu latu) were not correlated, but when functional rather than taxonomic groups were considered, pH and relative abundance of fish-eating species (Gaviidae and Podicipedidae) were correlated. However, the relative abundance of Bucephala clangula, a diving duck that may compete with fish for food, was not correlated with pH. Although individual species may be affected, community level responses of waterfowl to acidity are either absent or hard to detect at our sites.
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| 2. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Relationships between species number, lake size and resource diversity in assemblages of breeding waterfowl
- 1994
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Ingår i: Journal of Biogeography. - 0305-0270 .- 1365-2699. - 0305-0270 ; 21:1, s. 75-84
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Tidskriftsartikel (refereegranskat)abstract
- Breeding waterfowl, habitat diversity and food diversity were studied in 31 boreal lakes in Finland and Sweden. Lakes were 2-48 hectares in size, and had zero to eleven waterfowl species each. In all, sixteen species of Gaviiformes, Podicipediformes, Anseriformes and Fulica were recorded. The observed species distribution deviated from the 'null' expectation derived from a model of random placement, indicating a low importance of lake area per se. However, lake area was found to be a better predictor of species number than was length of shoreline, and lake area-species number regressions gave values between 0.255 and 0.345. We further evaluated 'the area per se (sampling)' hypothesis and 'habitat diversity' hypothesis separately by multiple stepwise regressions, in which lake area explained most of the variation in species number in species dependent on the lake for brood-rearing. Richness of more mobile species and of all species was best explained by the number of prey taxa encountered in the lake.
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| 3. |
- Nilsson, Anders N., et al.
(författare)
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Abundance and species richness patterns of predaceous diving beetles (Coleoptera, Dytiscidae) in Swedish lakes
- 1994
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Ingår i: Journal of Biogeography. - 0305-0270 .- 1365-2699. - 0305-0270 ; 21:2, s. 197-206
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Tidskriftsartikel (refereegranskat)abstract
- Abundance and species richness of dytiscid water beetles were estimated with activity traps in ten lakes each in south, central and north Sweden. Partial least square regression models with two significant components explained 76.5% and 55.8% of the total variance in dytiscid abundance and species richness, respectively. For abundance as well as species richness, component 1 had its highest positive loadings for structural complexity of vegetation and abundance of Asellus and Diptera immatures, and high negative loadings for relative shore depth. Component 2 had its highest positive loadings for fish abundance, number of dipterans in emergence traps and relative shore depth, and high negative loadings for lake area. Both the number of dytiscid individuals and species were higher in the northern lakes than in the two other regions. Smaller species were not more abundant in the traps than larger ones. Species mean abundance was positively correlated with number of lakes occupied.
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| 4. |
- Nummi, Petri, et al.
(författare)
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Habitat distribution of the mallard in relation to vegetation structure, food, and population density
- 1994
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Ingår i: Hydrobiologia. - 0018-8158 .- 1573-5117. - 0018-8158 ; 280:1, s. 247-252
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Tidskriftsartikel (refereegranskat)abstract
- The mallard (Anas platyrhynchos Linnaeus) is a generalist feeder, breeding in a wide range of habitats, yet showing considerable between site differences in density. Variations in density and habitat use may result from inter- and intra-specific competition, habitat structure or food. We studied habitat selection of the mallard in four regions of Finland and Sweden. In each region, ten lakes were chosen ranging from oligotrophic to eutrophic. Habitat distribution of the mallard did not differ between regions despite variation in the density of the species and congenerics. Mallard density did not correlate with vegetation structure, but increased with food abundance and the number and density of congenerics although there were regional differences in mallard response.
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| 5. |
- Pöysä, Hannu, et al.
(författare)
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Species composition of dabbling duck assemblages : ecomorphological patterns compared with null models
- 1994
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Ingår i: Oecologia. - 0029-8549 .- 1432-1939. - 0029-8549 ; 98:2, s. 193-200
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Tidskriftsartikel (refereegranskat)abstract
- Ecomorphological patterns of breeding dabbling duck (Anas spp.) assemblages were studied in six regions in northern Europe. Observed spacings among species in terms of bill lamellar density and body length were compared with expected spacings based on null models incorporating different levels of constraints (regional species pools, species relative abundances, lake size and habitat requirements of species). Deviations of observed spacings from expected ones were compared with prey abundance and prey size diversity in the lakes. Observed spacings in terms of body length, but not in terms of bill lamellar density, were greater than expected on the basis of null models. The most abundant species were generally relatively more different than less abundant species in terms of body length but not in terms of bill lamellar density. Deviations between observed and expected spacings in terms of body length were more like those predicted by the competition hypothesis in lakes with low food abundance than in lakes with high food abundance. Patterns in bill lamellar spacings were not related to food abundance nor to food size diversity. In general, patterns in body length spacings were consistent with the competition hypothesis whether the null model used in comparisons was constrained or not.
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| 6. |
- Ranta, Esa, et al.
(författare)
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Reinventing the wheel : analysis of sexual dimorphism in body size
- 1994
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Ingår i: Oikos. - 0030-1299 .- 1600-0706. - 0030-1299 ; 70:3, s. 313-321
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Tidskriftsartikel (refereegranskat)abstract
- Sexual dimorphism in body size has received increasing scientific interest during the past decade. In most of the papers on the subject, the magnitude of sexual size dimorphism is expressed as some conversion of body size ratio. There are several possible flaws in using such ratios, however, the most serious one concers the scaling of body size and size differences between sexes. Using ratios may easily lead to wrong conclusions. In this paper we emphasize some fallacies related to ratios and present a less biased method, based on residuals of linear regression. This method is suggested to be used in comparative analyses of sexual size dimorphism.
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