The links between dispersal and individual fitness: correlation or causality? : Exploring mechanisms using correlative and experimental approaches in a passerine bird species, the collared flycatcher

Abstract: Dispersal is commonly defined as the movement of an individual from its natal orprevious breeding site to a new breeding site. Because dispersal involves movements ofindividuals and genes among populations, it is recognized as a key life history trait withstrong effects on many ecological and evolutionary processes such as populationdynamics and genetics but also species spatial distribution or response to brutalenvironmental variations induced by human activities. Yet, the consequences of dispersalin terms of individual fitness remain poorly understood despite their crucial importance inthe understanding of the evolution of dispersal. The aim of this PhD is to get betterinsights in the fitness consequences of dispersal using both correlative and experimentalapproaches at different scales, i.e. annual and lifetime scales, in a wild patchy populationof migratory passerine bird, the collared flycatcher (Ficedula albicollis). Using a long-termdata set encompasses more than 20 years of data, differences between dispersing andphilopatric individuals were demonstrated both at a lifetime and annual scale. The resultsshowed strong phenotypic- and condition-dependent effects of dispersal and highlightthat the balance between the costs and benefits of dispersal is likely to be the result ofsubtle interactions between environmental factors and individuals’ phenotype. Moreover,the forced dispersal experiment demonstrated that dispersal might entail costs link tosettlement in a new habitat, which only some individuals may overcome. Nevertheless,the absence of difference in major fitness related decisions after settlement suggests thatdispersal is mostly adaptive for individuals overcome such costs.Key words: dispersal, fitness, collared flycatcher, dispersal costs and benefits,experimental approach, correlative approach, passerine.