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Within-season sequential density dependence regulates breeding success in mallards (Anas platyrhynchos)
Kristianstad University, Department of Mathematics and Science. (Akvatisk biologi och kemi)
Kristianstad University, Department of Mathematics and Science. (Akvatisk biologi och kemi)ORCID iD: 0000-0003-2345-3953
Finnish Game and Fisheries Research Institute, Joensuu Game and Fisheries Research.
Department of Animal Ecology, Swedish University of Agricultural Sciences, Umeå.
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2005 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 108, no 3, p. 582-590Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2005. Vol. 108, no 3, p. 582-590
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:hkr:diva-710DOI: 10.1111/j.0030-1299.2005.13618.xISI: 000226898200016OAI: oai:DiVA.org:hkr-710DiVA, id: diva2:210562
Available from: 2009-04-02 Created: 2009-04-02 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Survival patterns and density-dependent processes in breeding mallards Anas platyrhynchos
Open this publication in new window or tab >>Survival patterns and density-dependent processes in breeding mallards Anas platyrhynchos
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Measuring and assessing vital rates such as births and deaths are prerequisites for understanding population dynamics. Vital rates may be affected by the density of individuals, even though the importance of density dependence on population dynamics has been debated for a long time. The mallard Anas platyrhynchos is one of the foremost game species in the Holarctic, with millions of birds in hunters’ bags annually. Still, basic knowledge about regulation of mallards’ vital rates is poor, and experimental studies on this topic are rare.

In this thesis I have studied survival patterns and density dependence in mallards breeding in Sweden and Finland. Long-term ringing data from both countries were analysed for mortality patterns and causation, as well as for e.g. survival rate estimation. Most of the studies were, though, experiments run over two years involving manipulations of the density of nests, broods and/or adults, in southern and northern Sweden, comprising different biotic regions. Common response variables were survival of nests, ducklings and hens, mainly analysed with program MARK.

About 90% of the recovered mallards in Finland and Sweden were hunting kills. However, survival rates were high, ranging from 0.66 to 0.81 for most groups (sex*age). The generality of density dependence was evident since such processes were detected in all studies. Consequently, depredation rate was higher in high nest density compared to low nest density. Survival of ducklings was density-dependent in both boreal and nemoral biotic regions, with food limitation being evident in the former region but not in the latter. In spite of their generality, density-dependent patterns varied within as well between years, and for nest predation rates also between landscape types.

The findings about density dependence in breeding mallards in this thesis are novel since they are based on experiments. They are potentially of general interest for management because they embrace a variety of lakes in two geographically distant areas, each being representative for large temperate areas in the northern hemisphere. Detection of density dependence at the local scale may be important at larger scales, too, following the principle of ‘ideal preemptive distribution’ in a source-sink dynamic system.

Place, publisher, year, edition, pages
Umeå: Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, 2007. p. 39
Series
Acta Universitatis agriculturae Sueciae, ISSN 1652-6880 ; 2007:12
Keywords
broods, dabbling ducks, density dependence, ducklings, experiments, models, mortality, nest predation, regulation, survival
National Category
Ecology
Identifiers
urn:nbn:se:hkr:diva-6782 (URN)978-91-576-7311-4 (ISBN)
Public defence
2007-03-23, Sveriges Lantbruksuniversitet, Alnarp, 09:00 (English)
Opponent
Supervisors
Available from: 2010-08-24 Created: 2010-06-28 Last updated: 2014-06-05Bibliographically approved

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Elmberg, JohanGunnarsson, Gunnar

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