What are the strengths and limitations of direct and indirect assessment of dispersal? Insights from a long-term field study in a group-living bird species
Molecular methods of assessing dispersal have become increasingly powerful and have superseded direct methods of studying dispersal. Although now less popular, direct methods of studying dispersal remain important tools for understanding the evolution of dispersal. Here, we use data from Siberian jays Perisoreus infaustus, a group-living bird species, to compare natal dispersal distances and rates using visual mark–recapture, radio-tracking and microsatellite data. Siberian jays have bimodal natal dispersal timing; socially dominant offspring remain with their parents for up to 5 years (delayed dispersers), while they force their subordinate brood mates to leave the parental territory at independence (early dispersers). Early dispersers moved about 9,000 m (visual mark–recapture, radio-tracking) before settling in a group as a non-breeder. In contrast, delayed dispersers moved about 1,250 m (visual mark–recapture only) and mainly moved to a breeding opening. Dispersal distances were greater in managed habitat compared to natural habitat for both early and delayed dispersers. Molecular estimates based on 23 microsatellite loci and geographical locations supported distance estimates from the direct methods. Our study shows that molecular methods are at least 22 times cheaper than direct methods and match estimates of dispersal distance from direct methods. However, molecular estimates do not give insight into the behavioural mechanisms behind dispersal decisions. Thus, to understand the evolution of dispersal, it is important to combine direct and indirect methods, which will give insights into the behavioural processes affecting dispersal decisions, allowing proximate dispersal decisions to be linked to the ultimate consequences thereof.
KeywordsNatal dispersal Neighbourhood size Philopatry Biased dispersal Genetic population structure
We are grateful to Folke and May Lindgren for sharing dispersal data and their knowledge of Siberian jays with us, and to the late Gunnar Pavval for his hospitality at Lappugglan. We are thankful to Sönke Eggers, Magdalena Nystrand and Katya Dobrovolskaya for help in the field, to Szymon M. Drobniak for statistical advice, and to and Andreas Rudh for help in the lab. Ben Hatchwell, Jacob Höglund, Yang Liu, Tania Jenkins, Carles Vilà, Simone Webber, Mario Pesendorfer and an anonymous reviewer gave much appreciated advice in the lab or comments on the manuscript. Lantmäteriet provided aerial photographs for Fig. 1 under Uppsala University licence i2012/921.
The experiments comply with the current laws and were done under the licence of the Umeå Ethics Board (licence number A80-99 and A45-04).
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