| 1. |
- Elmberg, Johan, 1960-
(author)
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Density-dependent breeding success in mallards Anas platyrhynchos on a eutrophic lake
- 2003
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In: Wildlife Biology. - 0909-6396 .- 1903-220X. - 0909-6396 ; 9:1, s. 67-73
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Journal article (peer-reviewed)abstract
- Census data from a eutrophic lake collected in 1987-1999 were used to study nesting and breeding success in mallards Anas platyrhynchos. In each year there were 6-19 pair counts and 13-34 brood counts. The maximum combined count of single males and pairs (i.e. on any day in any of three census periods in May) provided the best fit with subsequent estimates of breeding success. Nesting success (average brood:pair ratio = 0.52), brood size of older ducklings (mean = 5.7) as well as fledgling success (2.86 juveniles per nesting pair) were higher than in many previous mallard studies. Per capita brood production as well as per capita fledgling production was negatively density dependent, but the latter was not statistically independent of the former. There was no correlation between per capita fledgling success and duckling mortality on a year-by-year basis, hence the density-dependent pattern in breeding success appears to be mediated through variation in nesting success. The number of paired females at the start of the breeding season correlated positively with the production of fledged juveniles the year before.
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| 2. |
- Palo, Thomas, et al.
(author)
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Spatial and temporal variations of Cs137 in moose Alces alces and transfer to man in northern Sweden
- 2003
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In: Wildlife Biology. - 0909-6396 .- 1903-220X. ; 9:3, s. 207-212
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Journal article (peer-reviewed)abstract
- The radioactive fallout from the Chernobyl accident in 1986 contaminated parts of the boreal forest ecosystems in Sweden, and we report on the activity concentration of radiocaesium 137Cs in the meat of moose Alces alces caught in the county of Västerbotten in north-Sweden during 1986-1996. Countywide, the geographic distribution patterns of 137Cs activity in moose muscle were similar in 1986 and 1993. The underlying relationship between 137Cs concentration in moose muscle and ground deposition remained significant for all years, but the proportion of variation explained by this relationship was variable and low in most years. The transfer rate of 137Cs to moose underwent marked annual fluctuations that appear to be synchronous over large areas. The fluctuations in the uptake of 137Cs by moose most probably result from variations in food selection or shifts in habitats. The transfer rate of 137Cs to moose seems to be higher in coastal areas than in inland areas. The 137Cs activity in moose was considerably higher in 1993 than should be expected from a simple decay model based on original deposition data and the 137Cs levels in moose meat from 1986. The large temporal variations in transfer rate make future predictions of transfer to moose and man unreliable. We found that the annual hunting of moose is a major source of 137Cs transfer to man in this region.
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| 3. |
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| 4. |
- Elmberg, Johan
(author)
-
Density-dependent breeding success in mallards Anas platyrhynchos on a eutrophic lake
- 2003
-
In: Wildlife Biology. - : Nordic Council for Wildlife Research. - 0909-6396. ; 9:1, s. 67-73
-
Journal article (peer-reviewed)abstract
- Census data from a eutrophic lake collected in 1987-1999 were used to study nesting and breeding success in mallards Anas platyrhynchos. In each year there were 6-19 pair counts and 13-34 brood counts. The maximum combined count of single males and pairs (i.e. on any day in any of three census periods in May) provided the best fit with subsequent estimates of breeding success. Nesting success (average brood:pair ratio = 0.52), brood size of older ducklings (mean = 5.7) as well as fledgling success (2.86 juveniles per nesting pair) were higher than in many previous mallard studies. Per capita brood production as well as per capita fledgling production was negatively density dependent, but the latter was not statistically independent of the former. There was no correlation between per capita fledgling success and duckling mortality on a year-by-year basis, hence the density-dependent pattern in breeding success appears to be mediated through variation in nesting success. The number of paired females at the start of the breeding season correlated positively with the production of fledged juveniles the year before.
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| 5. |
- Green, Martin, et al.
(author)
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Site use by dark-bellied brent geese Branta bernicla bernicla on the Russian tundra as recorded by satellite telemetry: implications for East Atlantic Flyway conservation
- 2002
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In: Wildlife Biology. - 0909-6396. ; 8:3, s. 229-239
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Journal article (peer-reviewed)abstract
- In 1999, seven dark-bellied brent geese Branta bemicla bemicla were followed during spring migration from western Europe to Arctic Russia using satellite telemetry. For six of the birds we were also able to monitor their summer stay at the Taymyr Peninsula, and for five birds part of their autumn migration was recorded. In this article, we report on site use during summer and spring/autumn migration. We also describe migration routes and evaluate general migratory performance during autumn migration. All birds spent the summer within areas covered by the Great Arctic Reserve on the Taymyr Peninsula. None of the birds returned to the wintering area with young, so the sites used during summer were most likely used primarily for moulting. The birds remained at the same sites the whole summer until the start of autumn migration, indicating that the build-up of fuel stores for migration took place at the moulting sites. Autumn migration was conducted in a similar way as spring migration regarding routes and general migratory performance. Site use showed both a relatively large variation between individuals and seasons, as well as some degree of site fidelity as all birds returned for a longer stay in autumn to at least one of the areas they had used for more than two days in spring. Thus the migration of brent geese along the Arctic Ocean cannot be considered as a simple migration system with just a few key sites along the route, but instead it is a complex system with several localities used in different ways by different individuals. Most of the areas used by the satellite-tagged birds were previously known stopover areas, but some of them had not been recognised as being of importance for brent geese before. Most of the stopover areas do not have any kind of formal legal protection. It is suggested that further research should be carried out in the areas identified in this study to evaluate their importance and role in the migratory journeys of dark-bellied brent geese.
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| 6. |
- Jonzén, Niclas, et al.
(author)
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Harvesting-induced population fluctuations?
- 2003
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In: Wildlife Biology. - 0909-6396. ; 9:1, s. 59-65
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Journal article (peer-reviewed)abstract
- It has recently been shown that damped endogenous dynamics is a common feature in Finnish grouse species; In this paper, we demonstrate that time-variant harvesting may turn damped dynamics to quasi-periodic fluctuations. Exploited populations, e.g. grouse, may therefore fluctuate more than expected if we do not manage to keep the harvest fraction constant over time. However, the harvest fraction of Finnish grouse varies with the phase of the cycle. Such a harvesting strategy could potentially change the periodicity of the fluctuations, as can a threshold harvest strategy where a constant fraction is harvested above a density threshold. The two non-linear harvesting strategies investigated here can modulate the dynamic properties of the population in a way not predicted by linear models. We argue that the behaviour of exploited populations and the role of harvesting can only be understood if we identify and understand the interplay of endogenous and exogenous components of population dynamics.
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| 7. |
- Jonzén, Niclas, et al.
(author)
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Harvesting spatially distributed populations
- 2001
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In: Wildlife Biology. - 0909-6396. ; 7:3, s. 197-203
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Journal article (peer-reviewed)abstract
- Spatial structure has a paramount influence on population dynamics. This has until recently been neglected in harvesting theory. In this paper, we demonstrate how source-sink and habitat selection theory can provide guidance for harvesting spatially structured populations. We also show how harvesting can affect the spatial distribution of the exploited resource, which has consequences for the design of protected areas. This implicit treatment of space is complemented by a spatially explicit predator-prey model. It turns out that harvesting of the prey and/or the predator species in one patch in space sometimes has effects on the other species outside the harvested patch. We stress the importance of considering how realistic the representation of the spatial dimension has to be in population management.
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| 8. |
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