| 1. |
- Elmberg, Johan, et al.
(författare)
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Within-season sequential density dependence regulates breeding success in mallards Anas platyrhynchos
- 2005
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Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 108, s. 582-590
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Tidskriftsartikel (refereegranskat)abstract
- Density dependence in vital rates is a key issue in population ecology but remains largely unexplored experimentally. We studied breeding success, lake use, and prey availability in wild mallards Anas platyrhynchos on small nemoral lakes in a replicated, two-year cross-over experiment in which pair density was increased. The number of wild mallards that settled on lakes prior to introductions of extra pairs did not differ between control and introduction years. Introductions led to a lake-level reduction in the number of broods observed. However, the number of stage 2/ (almost fledged) ducklings did not differ between treatments, nor did lake utilization by nonbreeding adults, broods and ducklings. Prey resource availability differed greatly among lakes, but it did not correlate with breeding success. Partialling out the possible effect of food competition from wild adult nonbreeding mallards did not change this conclusion. Our study demonstrates sequential density dependence in breeding success; introductions caused a decrease in brood number, but despite fewer broods a similar number of nearly fledged ducklings were produced. We suggest that predation and/or lake change of broods soon after hatching created these patterns. We conclude that using a single and late measure of breeding success such as fledged birds can mask regulatory processes. Implications of density dependence and its relation to individual reproductive success are understood better if breeding success is decomposed into nest success, duckling survival and fledgling survival.
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| 2. |
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| 3. |
- Arzel, Céline, et al.
(författare)
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Does foraging in Teal Anas crecca depend on season and disturbance by predators?
- 2006
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Ingår i: Integrating science and duck management. ; , s. 131-
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Konferensbidrag (refereegranskat)abstract
- To ensure wise management of migratory species it is crucial to know their energy requirements throughout their biological cycle, especially during periods like spring migration, that might affect future breeding success. Surprisingly, this period has seldom been studied. To start filling this gap for dabbling ducks and especially Eurasian Teal Anas crecca, we studied their foraging time and foraging methods along their Western European flyway from wintering to breeding grounds. Differences in foraging activity between sexes, species, years, seasons, sites and diel patterns were checked, as well as potential effects of disturbances by potential predators. Ducks of both sexes presented a fairly constant nocturnal foraging along the flyway, whereas diurnal foraging increased at periods of high requirements (spring, breeding, moulting). Ducks might thus not only be income breeders, but also income migrators (relying on the food they encounter along their flyway to fuel their travel). Moreover, Teal foraging depth increased along the flyway when disturbance due to potential predators decreased. This probably reflects their diet switch (from granivorous to carnivorous). The decrease in predator pressure probably makes it possible for teals to use riskiest behaviors (greater depths associated to eyes underwater and less prevention of predators).We thus highlight the need for adequate management of staging wetlands all along the flyway, since ducks have to fulfill high energy requirements there. Water level control may be useful to provide more shallow foraging habitats in which they can use less risky foraging techniques at times when nutrient needs increases and predation risk is relatively high.
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| 4. |
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| 5. |
- Elmberg, Johan
(författare)
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Bergand
- 2007
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Elmberg, Johan
(författare)
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Brånsjön - mer speciell än du tror!
- 2006
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Ingår i: Fåglar i Västerbotten. - Umeå. - 0348-1166. ; 31:1, s. 14-17
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 7. |
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| 8. |
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| 9. |
- Elmberg, Johan
(författare)
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Felbestämd korsnäbb
- 2007
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Ingår i: Vår fågelvärld. - 0042-2649. ; 66:3, s. 36-
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Elmberg, Johan, et al.
(författare)
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Nötkråka
- 2007
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 14. |
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| 15. |
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| 16. |
- Elmberg, Johan, et al.
(författare)
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Skedand
- 2007
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 17. |
- Elmberg, Johan, et al.
(författare)
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Stjärtand
- 2007
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 18. |
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| 19. |
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| 20. |
- Elmberg, Johan
(författare)
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Ärta
- 2007
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 21. |
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| 22. |
- Hettyey, Attila, et al.
(författare)
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Does testis weight decline towards the Subarctic? : a case study on the common frog, Rana temporaria
- 2005
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Ingår i: Die Naturwissenschaften. - 0028-1042 .- 1432-1904. ; 92:4, s. 188-192
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Tidskriftsartikel (refereegranskat)abstract
- Interpopulation comparisons of variation in resource availability and in allocation patterns along altitudinal and latitudinal gradients allow insights into the mechanisms shaping the life history of animals. Patterns of between-population differences in female life history traits have been studied intensively across a wide range of taxa, but similar investigations in males have remained scarce. To study if testis weight-a measure of reproductive investment-varies on a geographical scale in anurans, we focussed on the variation in relative testis weight (RelTW) and asymmetry in 22 populations of the common frog Rana temporaria along a 1,600-km latitudinal transect across the Scandinavian peninsula. We found that RelTW decreased towards the north. Body mass and body length both had independent positive effects on testes mass. We found evidence for directional asymmetry (DA) in testis weight with the right testis being larger than the left. The level of DA in testis weight was not related to latitude, but both body mass and testes mass had independent positive effects on asymmetry. We discuss the northwards decrease in RelTW in terms of a decreased reproductive investment as a possible consequence of harsher environmental conditions, and perhaps also, weaker sexual selection in the north than in the south.
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| 23. |
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| 24. |
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| 25. |
- Jönsson, K. Ingemar, 1959-, et al.
(författare)
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Radiation tolerance in the eutardigrade Richtersius coronifer
- 2005
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Ingår i: International Journal of Radiation Biology. - : Taylor & Francis. - 0955-3002 .- 1362-3095. ; 81:9, s. 649-656
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Tardigrades have a reputation of being extremely tolerant to extreme environmental conditions including tolerance to ionizing radiation while in a desiccated, anhydrobiotic state. However, the evidence for radio-tolerance in tardigrades is based on only one previous report, and there is an obvious need for complementary studies. In this paper we report an investigation on radio-tolerance in desiccated and hydrated specimens of the eutardigrade Richtersius coronifer.MATERIALS AND METHODS: Groups of 30 - 50 tardigrades were exposed to gamma-radiation at doses between 1.0 - 9.0 (anhydrobiotic animals) or 0.5 - 5.0 (hydrated animals) kGy and the animals were followed until all were dead. Radiation tolerance of both desiccated and hydrated tardigrades was studied.RESULTS: Both desiccated and hydrated animals irradiated with 0.5 and 1 kGy did not deviate in survival from the control groups. Animals from all exposed groups underwent their moulting and egg production cycle, but at decreasing frequency for doses above 1 kGy. No eggs laid by irradiated animals hatched, while eggs laid by controls did so.CONCLUSION: Our study suggests that radiation tolerance in tardigrades is not due to biochemical protectants connected with the desiccated state. Rather, cryptobiotic tardigrades may rely on efficient mechanisms of DNA repair, the nature of which is currently unknown.
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| 26. |
- Jönsson, K. Ingemar, 1959-
(författare)
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Tuffa djur prövas i rymden
- 2007
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Ingår i: Populär astronomi. - 1650-7177. ; 8:4, s. 10-
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 27. |
- Laugen, A T, et al.
(författare)
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Do common frogs (Rana temporaria) follow Bergmann's rule?
- 2005
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Ingår i: Evolutionary Ecology Research. - 1522-0613 .- 1937-3791. ; 7:5, s. 717-731
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Tidskriftsartikel (refereegranskat)abstract
- Questions: Does intraspecific extension of Bergmann's rule - larger size within a species in cooler areas - hold true for ectotherms in general, and for the common frog (Rana temporaria) in particular? What is the relative importance of genetic and environmental factors (i.e. direct environmental induction) in determining latitudinal patterns of body size variation in common frogs?Methods: We tested for a positive association between mean body size and latitude in common frogs (Rana temporaria) across a 1600 km long latitudinal gradient in Scandinavia both for wild-collected adults and laboratory-reared metamorphs.Results: In adults, the mean body size increased from south to mid-latitudes, and declined thereafter. This occurred despite the fact that the mean age of adult frogs increased with increasing latitude, and age and body size were positively correlated. The latitudinal pattern of body size variation in metamorphs reared in a common garden experiment was similar to that observed among wild-caught adults.Conclusions: The results suggest that the concave pattern of body size variation across the latitudinal cline may be at least partly genetically determined, and that although there is considerable geographic variation in mean body size of R. temporaria, this variation does not conform with Bergmann's rule.
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| 28. |
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