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- Delin, Anders
(författare)
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Naturvärden vid VOXNAN : Från Klucksjön till Vallhaga
- 1988
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Länsstyrelsen gav ifebruari 1984 Gävleborgs Botaniska Sällskap i uppdrag att inventera den 12 millånga outbyggda delen av VOXNAN mellan klucksjön och Vallhagaforsens kraftverk.Inventeringen skulle omfatta naturvärdena i stort, och framför allt debotaniska. Inventeringen utfördes under maj-september av fyrauniversitetsstuderande i botanik och åtta medlemmar i sällskapet, under ledningav Anders Delin. Denna rapport redogör för resultaten.
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| 5. |
- Lindgren, Gunilla
(författare)
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Bottenfaunan i några sjöar med varierande PH i Delsboområdet
- 1986
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Försurningen av sjöar och vattendrag är ett miljöproblem som orsakar stora biologiska skador i Sverige (Joansson m fl. 1981, Naturvårdsverket 1981 och 1982).Effekterna av försurning är flera och inbegriper bl. a att bottenfaunans sammanfattning ändras (Johannson m fl. 1981, Mossberg 1979) och att vissa djur slås ut och försvinner från systemet (Grahn och Hultberg 1974). Djurgrupper som man vet påverkas är t ex Chironomidae ( fjädermyggor)(Mossberg1979), Ephemeroptera (dagsländor) ( Engblom och Lingdell 1983), Gastropoda ( snäckor) ( Jokland 1980). Och Lamelliberanchiata( musslor) ( K A okland 1980). Genom att studera bl a dessa gruppers sammansättning kan man bedöma försurningsläget i en sjö.I denna rapport beskrivs bottenfaunan i ett antal sjöar med varierande ph i Delsboområdet. Sjöarna ingår i ett kalkningsprogram där två av sjöarna utgör okalkade referenssjöar. PÅ kort sikt är målsättningen med detta arbete att dokumentera bottenfaunan i dessa sjöar samt att göra en översiktlig bedömning av PH- situationen i sjöarna utifrån bottenfaunan.PÅ längre sikt är avsikten med undersökningen även att studera bottenfaunan i sjöarna i minst 3 år för att följa effekterna av de olika kalkningsåtgärderna som utförts i eller i anslutning till dem.
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| 6. |
- Nilsson, Jan-Åke, et al.
(författare)
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Early fledging mortality and the timing of juvenile dispersal in the marsch tit Parus palustris
- 1985
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Ingår i: Ornis Scandinavica. - : JSTOR. - 0030-5693. ; 16, s. 293-298
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Tidskriftsartikel (refereegranskat)abstract
- Family flocks of Marsh Tits Parus palustris in southern Sweden kept together until 11-15 d after fledging and stayed within the former territory of the parents. Mortality in the family flocks was low in one year (1.2-3.6%) but higher in another (18.6%). This level of mortality is compared with post-dispersal mortality in other species of tits. The occurrence of a parent-offspring conflict with regard to when juveniles should disperse is called in question. The level of aggression from parents towards their young was very low. Experimental broods of increased and reduced size stayed equally long within the parental territory, thus refuting the hypothesis that parents force their young to emigrate to avoid local competition for food or the harassment from the begging young. Dispersal of young from a family flock took place over more than one day. Late dis- persers were significantly smalller than their nestmates. This supports the hypothesis that dominant individuals disperse first, while subdominants stay longer in the safety of the parental territory to increase their self-feeding ability,
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- Nilsson, Jan-Åke, et al.
(författare)
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Effects of Dispersal Date on Winter Flock Establishment and Social Dominance in Marsh Tits Parus palustris
- 1988
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Ingår i: Journal of Animal Ecology. - : JSTOR. - 1365-2656 .- 0021-8790. ; 57:3, s. 917-928
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Tidskriftsartikel (refereegranskat)abstract
- (1) We studied the effect of sex, size, age and prior occupancy on social dominance winter flock establishment in a population of marsh tits Parus palustris L. (2) When sex was accounted for, time of establishment in the winter flock-prior occupancy, was critical for the outcome of later aggressive interactions juveniles within flocks. Residents won all interactions with intruders irrespective controlling for sex. (3) Success in, and timing of, establishment were closely linked with hatching lower proportion of late-hatched than early-hatched juveniles became established winter flocks; they also became established later. Even small differences in hatching greatly influenced dominance and the probability of becoming established flock. (4) Since early establishment depends on early hatching, dominance and survival juveniles are determined by how early their parents start breeding. Furthermore, will be strong selection for quick establishment after
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- Nilsson, Jan-Åke, et al.
(författare)
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Incubation feeding as a male tactic for early hatching
- 1988
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Ingår i: Animal Behaviour. - 1095-8282. ; 36:3, s. 641-647
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Tidskriftsartikel (refereegranskat)abstract
- Male marsh tits, Parus palustris, regularly feed their mates from the beginning of nest building until hatching. Over three periods (the 15 days preceding egg formation, egg formation/laying and incubation) the number of food passes by the male to the female increased significantly. There was a significant negative relationship between the frequency with which the male fed the female in the nest during incubation and the length of the incubation period. Female blue tits, Parus caeruleus, experimentally supplied with food in the nestbox during incubation had a significantly shorter incubation period than control females. Clutches of experimentally fed females also tended to hatch more successfully. It is concluded that feeding of the female by the male is a nutritional contribution and that the shorter incubation period and increased hatching success enhance the fitness of both parents. However, the male should balance the benefits against the costs in time and energy and therefore not necessarily work at a maximal level. In accordance with this is the finding that the male's provisioning rate increased when ambient temperatures decreased. Adverse weather may jeopardize the whole or large proportions of the clutch, thereby significantly reducing the benefit from the current breeding attempt.
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- Sandström, Olof, 1945-
(författare)
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The ecology of the plankton fauna in the Gulf of Bothnia
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The geographical distribution of the Gulf of Bothnia zooplankton species is presented together with observations of abundancies and vertical distributions. The historical development of this plankton community in the last 70 years is discussed.Spring and summer development of the plankton fauna was studiedin the Bothnian Bay. Compared to in southern parts of the Balticit could be shown that the start of development in spring formany species was only moderately later in the Bothnian Bay. Theperiod of maximal biomass was in late summer and autumn.In a study of horizontal distribution large between-station variations were found. These variations were not random as close stations formed homogenous groups. Several cases of patchiness were established. Systematically appearing differences in age-distributions were proposed as a factor in the formation of patchiness.The selective prédation on zooplankton by Baltic herring was studied in the Bothnian Bay. Besides chosing certain species herring selects the older and larger stages of these species. Egg-bearing Eurytemora females were more heavily preyed upon than the males.From literature information and own observations it was proposed that in sence of production the Bothnian Bay and the Bothnian Sea are two very different systems. Climatic effects cause a delay of primary production in spring enabling the pelagic consumers to develop in phase with the producers in the Bothnian Bay. Contrary to systems with a spring peak in phytoplankton growth this situation will lead to high pelagial efficiency leaving little to feed the benthic communities.
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