Metapopulation‐level analyses reveal positive fitness consequences of immigration in a small bird

Dispersal links eco-evolutionary dynamics of subpopulations in fragmented landscapes and may play a crucial role in the viability of populations by increasing individual fitness and subpopulation growth rates. However, knowledge of individual fitness of immigrants and residents and their offspring at the local and metapopulation levels is often lacking due to the difficulty of quantifying fitness in geographically structured wild populations, which requires extensive field efforts. A comprehensive dataset that includes more than 15 years of individual capture-mark-recapture information and a high-resolution SNP-based pedigree from an insular wild house sparrow (Passer domesticus) metapopulation, was used to examine the fitness consequences of successful immigration for parent and offspring generations, and assess the relative contributions of immigrants and residents to the local pool of recruits versus individuals that recruited in other populations within the metapopulation. We show that immigrants produced more recruiting offspring annually and during their lifetime than residents. Moreover, we found that hybrid recruits (produced by immigrant-resident parents) had higher adult survival and produced more recruiting offspring during their lifetime than recruits produced by two resident or two immigrant parents. Additionally, although contributions to the local pool of recruits did not differ between immigrant and resident parents during their lifetime, immigrant parents produced more offspring that recruited in other populations than resident parents. Our results indicate that the benefits of being an immigrant last at least through the first offspring generation. Such positive fitness effects of immigrants may improve local population viability as well as metapopulation viability. Our study shows the importance of quantifying fitness of successful immigrants at a wide geographic scale in structured populations, because it may be difficult to a priori predict whether dispersers and residents contribute similarly or differently to the dynamics at local population and metapopulation levels.