| 21. |
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| 22. |
- Berglund, Anders, et al.
(författare)
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Biotic and abiotic factors determining the distribution of two prawn species: Palaemon adspersus and P. squilla
- 1981
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Ingår i: Oecologia. - 0029-8549 .- 1432-1939. ; 49:3, s. 300-304
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Tidskriftsartikel (refereegranskat)abstract
- The reasons behind the absence of the prawn Palaemon adspersus and the presence of P. squilla in rockpools and on bare sand bottoms were studied. Some maximal abundances in different habitats are given. Introduction experiments into natural and artificial rockpools and measurements of tolerance towards low oxygen levels showed that nocturnal hypoxia excluded P. adspersus which was significantly more sensitive to oxygen depletion. Respiration rates measured by the closed-bottle method showed no interspecific difference. On bare sand bottoms P. aspersus was probably excluded by predators, since predator exclusion experiments in cages and predator inclusion experiments in containers showed that P. adaspersus was more vulnerable to predation than P. squilla.The costs for being able to cope with a wide array of habitat in P. squilla are probably balanced by the benefits of access to habitats such as intertidal rockpools, very shallow bottoms and deeper sand bottoms. Tolerance towards abiotic factors extends its habitat range upwards into shallower waters, and tolerance towards biotic factors, i.e. predation, extends it downwards.
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| 23. |
- Berglund, Anders
(författare)
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Coexistence, size overlap and population regulation in tidal vs non-tidal Palaemon prawns
- 1982
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Ingår i: Oecologia. - 0029-8549 .- 1432-1939. ; 54:1, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- The effect of increased habitat heterogeneity in tidal areas on coexistence between Palaemon prawns was studied at eight sites along the European Atlantic coast. Two species which are sympatric in non-tidal areas, Palaemon adspersus Rathke and P. squilla (L.) are largely allopatric in tidal areas, and the sympatric size difference decreases in allopatry. In tidal areas the smaller species, P. squilla, is restricted to brown algal belts and rockpools. A third species, P. serratus (Pennant), larger than the others, occurs under oceanic salinities in subtidal brown algal belts and there has forced P. squilla to restrict its habitat distribution to adjacent intertidal rockpools. At estuarine salinities, however, P. squilla also inhabits the brown algal belts. A larger diel variation in stomach fullness index in P. squilla than in P. adspersus persists in non-tidal areas. Abiotic factors probably restrict the two largest species, viz. P. adspersus and P. serratus, to subtidal environments; these species are sensitive to the extremes in salinity, temperature or O2 levels characteristic of the intertidal zone. Competition and/or predation probably relegates P. squilla to the intertidal zone. In non-tidal areas, where this zone is reduced, P. squilla increases its niche width and coexists with P. adspersus, and the size differentiation associated with sympatry may reduce interspecific competition.
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| 24. |
- Berglund, Anders, et al.
(författare)
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Genetic differentiation in populations of two Palaemon prawn species at the Atlantic east coast : does gene flow prevent local adaptation?
- 1983
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Ingår i: Marine Biology. - 0025-3162 .- 1432-1793. ; 77:1, s. 49-57
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Tidskriftsartikel (refereegranskat)abstract
- Two Palaemon prawn species, P. adspersus Rathke and P. squilla (L.), occur along the European Atlantic coast. In areas heavily affected by tides (Netherlands and France), one species, P. squilla, inhabits the intertidal zone, and P. adspersus is found subtidally in the Zostera marina meadows. In areas with small tidal ranges (Sweden) both species occur in the Z. marina zone, and here the body size of P. squilla is reduced, something that in turn reduces reproductive output in this species. Is adaptive improvement in non-tidal P. squilla populations prevented by too extensive gene flow from tidal areas? To wanswer this, genetic differentiation was studied by horizontal starch gel electrophoresis. Each of the two species was sampled at five sites along the European Atlantic coast. Twenty-two enzymes representing 25 loci were scored. Significant genetic heterogeneity between sites was found in both species. Thus the extensive gene flow hypothesis was not supported by the results, and non-tidal populations ought to have the possibility to adapt to local conditions.
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| 25. |
- Berglund, Anders, et al.
(författare)
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Mate choice, fecundity and sexual dimorphism in two pipefish species (Syngnathidae)
- 1986
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Ingår i: Behavioral Ecology and Sociobiology. - 0340-5443 .- 1432-0762. ; 19:4, s. 301-307
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Tidskriftsartikel (refereegranskat)abstract
- In order to understand the causes of sexual dimorphism, mate choice and size-related fecundity were studied in two pipefish species, Syngnathus typhle and Nerophis ophidion. Sexual dimorphism is more pronounced in N. ophidion; females are larger, have sexual colourings, and are more active during courtship. In S. typhle the sexes are alike in all these respects. Males brood their offspring in both species. In N. ophidion fecundity was positively correlated with both body size and the amount of sexual colouring in females. In males no correlation between body size and fecundity, or between body size and embryo size existed. Predictably, in mate choice experiments with equal-sized females, males chose females with more extensive sexual colourings. We explain sexual dimorphism in this species as a consequence of both natural selection (fecundity increases with size in females but not in males) and sexual selection (males prefer larger females). We argue that sexual size dimorphism did not evolve by selection minimizing overlap in food niches between the sexes, because food production is high in the Zostera beds where the fishes live, and no size dimorphism was found in the sympatrically occurring S. typhle. Furthermore, in N. ophidion dimorphism is not greater in a particular mouth character than in overall body size. In S. typhle egg size and the average number of eggs transferred per spawning were positively correlated with female body size. Apparently more energy per offspring was provided by larger males than by smaller males, and larger males also carried more offspring. As predicted, large mates were preferred by both sexes in mate choice experiments. This is explicable in terms of both natural selection (fecundity increases with size in both sexes) and sexual selection (both sexes prefer large mates). As a consequence of selection acting in the same direction in both sexes, sexual dimorphism is absent in S. typhle.
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| 26. |
- Berglund, S., et al.
(författare)
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Arsenopyrite and sphalerite as T-P indicators in sulfide ores from northern Sweden
- 1980
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Ingår i: Mineralium Deposita. - 0026-4598 .- 1432-1866. ; 15:2, s. 175-187
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Tidskriftsartikel (refereegranskat)abstract
- The compositions of arsenopyrite and sphalerite from five Swedish metamorphosed Cu, Zn-sulfide deposits are related to T and P, according to the methods described by Kretschmar and Scott (1976) and Scott (1973). The As/S ratio of arsenopyrite indicates an equilibrium temperature around 400°C for all the deposits studied, whereas the sphalerite barometer shows pressures between 5 and 7 kb. The mineral assemblages of the bedrocks indicate a similar temperature but a lower pressure. A constant fs2 is probably only effective over distances of millimetres or a few centimetres in the samples studied. The fs2 has always been lower in the surrounding rocks than in the ores as indicated by a higher As/S in arsenopyrite, more FeS in sphalerites and the absence of pyrite.
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| 27. |
- Bergqvist, David, et al.
(författare)
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The economics of general thromboembolic prophylaxis
- 1988
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Ingår i: World Journal of Surgery. - 1432-2323. ; 12:3, s. 349-355
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Tidskriftsartikel (refereegranskat)abstract
- The clinical and economic effects of each of 3 alternatives—no prophylaxis, general prophylaxis, and selective treatment—have been assessed in conjunction with 3 types of surgery—general surgery, the subset surgery for cholelithiasis, and elective hip surgery. The costs of thromboembolic and hemorrhagic complications have been calculated from the figures for 28 patients hospitalized at the Department of Surgery, Malmö General Hospital, Malmö, Sweden. The anticipated number of thromboembolic complications—and thus even the number of fatal pulmonary embolisms—can be minimized in all 3 types of surgery by means of general prophylaxis. General prophylaxis with low-dose heparin is, however, accompanied by the greatest incidence of hemorrhagic complications. Health care costs are minimized with general prophylaxis in elective hip and general surgery, while no prophylaxis is the best alternative in surgery for cholelithiasis. From the patient's point of view, general prophylaxis minimizes the duration of thromboembolic disease in general surgery as well as in elective hip surgery. In surgery for cholelithiasis, however, no differences in health loss for the individual are shown between the 2 main alternatives, no prophylaxis and general prophylaxis. Selective treatment means treatment after diagnosis of thrombosis with some screening method. The alternative selective treatment was the least satisfactory of those 3 studied.
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| 28. |
- Bertin, G., et al.
(författare)
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Global spiral modes in stellar disks containing gas
- 1988
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 195, s. 105-113
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Tidskriftsartikel (refereegranskat)abstract
- The authors present a linear study of the role of gas on global spiral modes in stellar disks using a simple two-fluid model. The local destabilizing role of a cold component has been known for many years and calculated by various authors. The authors confirm the effectiveness of a small amount of gas in fueling spiral instabilities with a response which is primarily at short wavelengths by constructing a synthetic diagram which summarizes the local stability analysis. Then they proceed to consider global spiral modes in two-component systems with applications to regimes of astrophysical interest that are expected to be associated with normal spiral structure. Moderate growth spiral modes are found that are very close in structure to those of one-component systems, but for substantially higher values of the stability parameter Q. A simple model of self-regulation is also presented.
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| 29. |
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| 30. |
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