Summary:

Dispersal propensity may vary considerably between individuals in a population. Still, dispersal remains one of the least understood processes in ecology and evolution. In this study, we investigate individual variation in juvenile movement during the onset of the dispersal phase in four insular house sparrows Passer domesticus populations in northern Norway. The predictors were clutch size, hatch day, sex and morphology. The study islands differ in degree of patch isolation, configuration of suitable habitat, and characteristics of the matrix habitat. Thus, it was possible to assess the importance of such landscape features on movement. On one of the islands, movement rate was negatively related to hatch day. This pattern may be generated by age-dependent movement since early born individuals are older when the dispersal phase is initiated. However, we suggest that this relationship rather is a result of seasonal variation in the environment experienced by the nestlings, which affects their phenotype and propensity to disperse. Clutch size, sex, body size, mass and condition did not significantly explain variation in movement. On the other hand, movement rate seemed to decrease with increasing patch isolation, i.e. distance between patches and hostility of the matrix habitat. This suggests that habitat configuration is an important factor influencing movement and dispersal capacities of juvenile house sparrows.

Summary:

In age-structured populations, viability and fecundity selection of varying strength may occur in different age classes. On the basis of an original idea by Fisher of weighting individuals by their reproductive value, we show that the combined effect of selection on traits at different ages acts through the individual reproductive value defined as the stochastic contribution of an individual to the total reproductive value of the population the following year. The selection differential is a weighted sum of age-specific differentials that are the covariances between the phenotype and the age-specific relative fitness defined by the individual reproductive value. This enables estimation of weak selection on a multivariate quantitative character in populations with no density regulation by combinations of age-specific linear regressions of individual reproductive values on the traits. Demographic stochasticity produces random variation in fitness components in finite samples of individuals and affects the statistical inference of the temporal average directional selection as well as the magnitude of fluctuating selection. Uncertainties in parameter estimates and test power depend strongly on the demographic stochasticity. Large demographic variance results in large uncertainties in yearly estimates of selection that complicates detection of significant fluctuating selection. The method is illustrated by an analysis of age-specific selection in house sparrows on a fitness-related two-dimensional morphological trait, tarsus length and body mass of fledglings.

Summary:

Translocations are increasingly used in conservation programmes to reinforce small populations. Success of translocations in relation to characteristics of the species, the location or the translocation event, such as propagule size, is well studied. However, much less is known about individual variation in genetic contribution to the release population. Here, we compare sex-specific fitness of resident and introduced individuals based on genetic parentage, following a translocation experiment in house sparrows. The genetic mating pattern revealed assortative mating based on origin, where introduced males were highly unlikely to mate with resident females. Introduced males had fewer mates and fledglings than resident males. Origin had no effect on number of fledglings in females. The effect of origin on number of fledglings was sex-specific as indicated by the significant interaction between sex and origin. The number of recruits and total annual fitness contribution did not differ between resident and introduced individuals. In the house sparrow, male badge size has a function in intra- and intersexual selection. It is likely that the influence of badge size is of greater importance for introduced males, which have to compete with resident males over nest sites and mates. However, the relationship between number of mates and badge size did not differ between resident and introduced males. Still, the effect of badge size on number of fledglings was stronger in introduced males. Our results provide insights about sex-specific individual heterogeneity in reproductive success of introduced individuals, and the potential role of sexually selected traits for the genetic consequences of a translocation event.

Summary:

When investigating parasite-host dynamics in wild populations, a fundamental parameter to investigate is prevalence. This quantifies the percentage of individuals infected in the population. Investigating how prevalence changes over time and space can reveal interesting aspects in the parasite-host relationship in natural populations. We investigated the dynamic between a common avian parasite (Syngamus trachea) in a host metapopulation of House Sparrows (Passer domesticus) on the coast of Helgeland in northern Norway. We found that parasite prevalence varied in both time and space. In addition, the parasite prevalence was found to be different between demographic groups in the local populations. Our results reveal just how complex the dynamic between a host and its parasite may become in a fragmented landscape. Although temperature may be an important factor, the specific mechanisms causing this complexity are not fully understood, but needs to be further examined to understand how parasite-host interactions may affect the ecological and evolutionary dynamics and viability of host populations.