| 1. |
- Carlsson, Anna K, 1966, et al.
(författare)
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Shifts and widths of metal-overlayer quantum-well states near EF observed by photoemission
- 1994
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 50:12, s. 8926 - 8929
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron energy spectra reveal discrete valence-electron states in the range 0–220 meV above EF for 1–3 atomic layers of Na on Cu(111). Apart from a stepwise dependence on the number of atomic Na layers the energy of the quantum-well states depends in a gradual manner on how full the layer is. The states are as well defined in energy as comparable surface states producing peak widths (50–90 meV), which depend on temperature and coverage.
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| 2. |
- Nilsson, Jan-Åke, et al.
(författare)
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Causes and consequences of egg mass variation between and within blue tit clutches
- 1993
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Ingår i: Journal of Zoology. - : Wiley. - 1469-7998 .- 0952-8369. ; 230:3, s. 469-481
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Tidskriftsartikel (refereegranskat)abstract
- Causes of egg‐size variation between and within clutches were studied in clutches of the blue tit (Parus caeruleus L.). We measured the mass of each egg in the laying sequence in unmanipulated clutches, in clutches of parents experimentally supplied with extra food before egg‐laying, and in clutches of parents supplemented with extra food after the start of egg‐laying. Hatchlings were weighed at an age of two days and their mass was found to be positively related to egg mass. No general trend of decreasing or increasing egg mass was found within the laying sequence. Females provided with extra food before egg‐laying laid clutches with significantly less variation in egg mass than did control females. The reason for this was that the first‐laid egg of unmanipulated females was lighter than the rest of the eggs in the clutch. This pattern disappeared in clutches of females receiving extra food. Thus, the reduction in egg mass variation among clutches of foodsupplemented females depended on an ability of these females, in contrast to control females, to lay a first egg of the same mass as the rest of the clutch. Eggs laid after the initiation of incubation were significantly heavier than equivalent eggs in those clutches where incubation started after clutch completion. The difference was small, however, and the adaptive significance of the finding is questionable. We argue that intra‐clutch variation in egg mass is connected with greater fitness consequences than in inter‐clutch variation. Furthermore, our results indicate that energetical constraints on the laying female are more important as a cause of the observed intra‐clutch variation in egg mass than are adaptive responses to the environment.
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| 3. |
- Nilsson, Jan-Åke, et al.
(författare)
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Energetic constraints and ultimate decisions during egglaying in the blue tit
- 1993
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Ingår i: Ecology. - : Wiley. - 0012-9658. ; 74:1, s. 244-251
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Tidskriftsartikel (refereegranskat)abstract
- In a population of Blue Tits, Parus caeruleus, we performed two different food provisioning experiments; one starting before clutch initiaition and one starting when the first eggs were laid. We assessed the effect of these feeding experiments on four fitness—related factors, viz., laying date, clutch size, egg mass, and onset of incubation. Given that breeding birds are food and energy constrained, extra food during the breeding season should be invested in the fitness—related factor(s) that is most important for maximization of overall fitness. In the first feeding experiment, when breeding pairs had access to extra food both before and during egg—laying, the female converted this extra energy into earlier laying dates. When food was provided after clutch initiation only, the above preferred option was no longer available. In this situation, females used the extra energy to start incubating earlier in the laying sequence, with no influence on the other factors studied. Thus, both experiments resulted in surplus energy being used to increase the quality of the offspring instead of their number. In both cases the quality was connected with time savings leading to earlier hatching dates.
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| 4. |
- Nilsson, Jan-Åke, et al.
(författare)
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The frequency and timing of laying gaps
- 1993
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Ingår i: Ornis Scandinavica. - : JSTOR. - 0030-5693. ; 24:2, s. 122-126
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Tidskriftsartikel (refereegranskat)abstract
- The frequency of laying gaps was studied in a nestbox breeding population of Blue Tits Parus caeruleus during the breeding season of 1990. In as many as 27% of the 55 clutches studied, laying was interrupted for at least one day. It is concluded that the interruption of egg laying depends on food availability since the frequency of laying gaps decreased in clutches laid by females experimentally provided with extra food. Most gaps occurred after the laying of the first or second egg, indicating that each female started egg laying on the verge of what is possible for uninterrupted laying. The occurrence of laying gaps was not connected with certain dates, female age, clutch size or mean egg mass of the clutch, instead each female seemed to individually optimize the start of egg laying in relation to the risk of interrupted laying. To some extent the female is able to save energy for egg production because an egg laid after a gap was heavier than corresponding eggs laid in clutches without gaps. Furthermore, eggs laid immediatelly before a gap were lighter than equivalent eggs in other clutches, indicating that females, to some extent, are willing to trade egg quality against uninterrupted laying.
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| 5. |
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