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- Söderquist, Pär, et al.
(författare)
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Wild Mallards have more ”goose-like” bills than their ancestors
- 2015
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Ingår i: 4th Pan-European Duck Symposium, Hangö, Finland, 7-11/4, 2015. ; , s. 38-
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Konferensbidrag (refereegranskat)abstract
- Wild populations of the world’s most common dabbling duck, the Mallard (Anas platyrhynchos), run the risk of genetic introgression by farmed conspecifics released for hunting purposes. We tested whether bill morphology of free-living birds has changed since large-scale releases of farmed Mallards started. Three groups of Mallards from Sweden, Norway and Finland were compared: historical wild (before large-scale releases started), present-day wild, and present-day farmed. Higher density of bill lamellae was observed in historical wild Mallards (only males). Farmed Mallards had wider bills than present-day and historical wild ones. Present-day wild and farmed Mallards also had higher and shorter bills than historical wild Mallards. Present-day Mallards thus tend to have more ‘‘goose-like’’ bills (wider, higher, and shorter) than their ancestors. Our study suggests that surviving released Mallards affect morphological traits in wild population by introgression. We discuss how such anthropogenic impact may lead to a maladapted and genetically compromised wild Mallard population. Our study system has bearing on other taxa where large-scale releases of conspecifics with ‘alien genes’ may cause a cryptic invasive process that nevertheless has fitness consequences for individual birds.
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- Elmberg, Johan, et al.
(författare)
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Density dependent breeding success in mallards
- 2003
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Konferensbidrag (refereegranskat)abstract
- Breeding success in wild mallards was studied on small eutrophic nemoral lakes in a two-year cross-over experiment in which wing-clipped conspecifics were added to increase pair density. The number of wild mallards that came to the lakes to nest (prior to introductions) did not differ between years. Introduction treatment led to a significant reduction in brood number in wild mallards, but it did not alter the number of stage 2+ ducklings finally produced on a lake. Introduction had no effect on lake utilization by broods, ducklings and non-breeding adults (cumulative days over the entire breeding season). Abundance of invertebrate prey differed greatly among lakes, but it did not correlate with breeding success. Breeding success was thus subject to sequential density-dependence; i.e. a lower number of broods still produced the same number of 2+ ducklings. We speculate that predation is the most likely process behind both patterns. We conclude that late and snapshot measures of duckling productivity may mask density dependent population processes of fundamental importance to regulation and harvest policy.
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- Elmberg, Johan, et al.
(författare)
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Farmed European mallards are genetically different and cause introgression in the wild population following releases
- 2016
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Konferensbidrag (refereegranskat)abstract
- The practice of restocking already viable populations to increase harvest potential has since long been common in forestry, fisheries and wildlife management. The potential risks of restocking native species have long been overshadowed by the related issue of invasive alien species. However, during the last decade releases of native species with potentially non-native genome have received more attention. A suitable model to study genetic effects of large-scale releases of native species is the Mallard Anas platyrhynchos, being the most widespread duck in the world, largely migratory, and an important quarry species. More than 3 million unfledged hatchlings are released each year around Europe to increase local harvest. The aims of this study were to determine if wild and released farmed Mallards differ genetically, if there are signs of previous or ongoing introgression between wild and farmed birds, and if the genetic structure of the wild Mallard population has changed since large-scale releases started in Europe in the 1970s. Using 360 Single Nucleotide Polymorphisms (SNPs) we found that the genetic structure differed among historical wild, present-day wild, and farmed Mallards in Europe. We also found signs of introgression in the wild Mallard population, that is, individuals with a genetic background of farmed stock are part of the present free-living population. Although only a small proportion of the released Mallards appears to survive to merge with the free-living breeding population, their numbers are still so large that the genetic impact may have significance for the wild population in terms of individual survival and longterm fitness.
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8. |
- Gunnarsson, Gunnar, et al.
(författare)
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Experimental evidence for density-dependent breeding success in mallards
- 2005
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Konferensbidrag (refereegranskat)abstract
- It is unresolved to what extent waterfowl populations are regulated by density-dependent pro cesses. By doing a 2-year crossover perturbation exper iment on ten oligotrophic boreal lakes we addressed the hypothesis that breeding output is density depen dent. Wing-clipped mallard (Anas platyrhynchos) hens were introduced with their own brood and then moni tored for 24 days. Predicted responses were that per capita duckling and hen survival would be lower in high-density than in low-density treatments. Survival was evaluated by model fitting in program MARK. Density, year, and lake were used as main effects, while day after introduction, a weather harshness index, and presence of hens were covariates. Daily survival in ducklings was lower in the high-density treatment, but this effect was year dependent. The highest-ranking model for duckling survival also included a positive effect of duckling age and presence of hens, and a nega tive effect of harsh weather. Density did not affect female survival although there was a prominent year effect. The highest-ranking model for female survival also included negative effects of day after introduction and harsh weather. This is the first study to report den sity-dependent survival in experimentally introduced ducklings in a natural setting. Implications for population dynamics and management of harvested populations are far-reaching if such regulation occurs in some years, but not in others.
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9. |
- Gunnarsson, Gunnar, et al.
(författare)
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Food limits survival in breeding mallards
- 2003
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Ingår i: Integrating wildlife with people, 10th International Perdix Symposium, Braga, Portugal, September 1st-6th 2003. - Braga : International Union of Game Biologists.
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Konferensbidrag (refereegranskat)
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10. |
- Gunnarsson, Gunnar, et al.
(författare)
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Food limits survival of breeding boreal mallards Anas platyrhynchos
- 2003
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Konferensbidrag (refereegranskat)abstract
- During the breeding period dabbling ducks (Anas sp.), and especially newly hatched ducklings, face heavy mortality. The reasons are not clear, but suggested factors contributing are scarce food, predation, chilling and disease. We highlighted the question why many of the boreal lakes in Scandinavia are without breeding ducks and why mortality is considerable during brood period. In an experimental study in 2002 we hypothesized food being a major factor deciding duck survival during breeding. One wing-clipped hen mallard with her own newly hatched brood (10 ducklings) was introduced onto each of 10 lakes. Food was added ad libitum at 5 of these lakes (experimental lakes), whereas the other five lakes (controls) did not get any extra food added. Survival of hens, broods as well as each individual duckling was monitored regularly until 24 days after introduction. At all three levels (i.e. duckling, brood and adult), survival was significantly higher on lakes with food added than on control lakes, although the difference was most pronounced on the duckling level. Direct consequences (i.e. dying from starvation) as well as indirect (e.g. undernourished individuals being more easily taken by predators) may both explain this pattern. Our results clearly show that food is a major limiting factor on mallard survival in this environment. Also, our results may explain why many boreal lakes in Scandinavia do not have any breeding waterfowl at all. It seems likely that such lakes are too poor to raise broods and even to sustain adults.
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