Numerous hypotheses have been proposed to explain variation in reproductive performance and local recruitment of animals. While most studies have examined the influence of one or a few social and ecological factors on fitness traits, comprehensive analyses jointly testing the relative importance of each of many factors are rare. We investigated how a multitude of environmental and social conditions simultaneously affected reproductive performance and local recruitment of the red-backed shrike Lanius collurio (L.). Specifically, we tested hypotheses relating to timing of breeding, parental quality, nest predation, nest site selection, territory quality, intraspecific density and weather. Using model selection procedures, predictions of each hypothesis were first analysed separately, before a full model was constructed including variables selected in the single-hypothesis tests. From 1988 to 1992, 50% of 332 first clutches produced at least one fledgling, while 38.7% of 111 replacement clutches were successful. Timing of breeding, nest site selection, predation pressure, territory quality and intraspecific density influenced nest success in the single-hypothesis tests. The full model revealed that nest success was negatively associated with laying date, intraspecific density, and year, while nest success increased with nest concealment. Number of fledglings per successful nest was only influenced by nest concealment: better-camouflaged nests produced more fledglings. Probability of local recruitment was related to timing of breeding, parental quality and territory quality in the single-hypothesis tests. The full models confirmed the important role of territory quality for recruitment probability. Our results suggest that reproductive performance, and particularly nest success, of the red-backed shrike is primarily affected by timing of breeding, nest site selection, and intraspecific density. This study highlights the importance of considering many factors at the same time, when trying to evaluate their relative contributions to fitness and life history evolution.
We analyzed more than 1,600 dispersal events from two populations of a North American cooperatively breeding woodpecker species to determine what factors influence natal dispersal distance and whether distance traveled affects reproduction later in life. We found significant heritability of natal dispersal distance, in both males and females, indicating substantial additive genetic variance for this behavioral trait. Natal dispersal distance additionally was affected by social and ecological factors: individuals dispersing in their first year of life moved longer distances than those staying on their natal site as helpers for a prolonged time prior to dispersal, and increasing territory isolation led to longer dispersal distances. Successful dispersers incurred fitness costs, with lifetime fledgling production (in both sexes) and lifetime production of recruits to the breeding population (in females only) decreasing with increasing natal dispersal distance. We conclude that natal dispersal distance has a genetic basis but is modulated by environmental and social factors and that natal dispersal distance in this species is (currently) under selection.
Species often occur in subdivided populations as a consequence of spatial heterogeneity of the habitat. To describe the spatial organization of ubpopulations, existing theory proposes three main population models: patchy population, metapopulation and isolated populations. These models differ in their predicted levels of connectivity among subpopulations, and in the risk that a subpopulation will go extinct. However, spatially discrete subpopulations are commonly considered to be organized as metapopulations, even though explicit tests of metapopulation assumptions are rare. Here, we test predictions of the three models on the basis of demographic and genetic data, a combined approach so far surprisingly little used in mobile organisms. From 2002 to 2005, we studied nine subpopulations of the wetland-restricted reed bunting (Emberiza schoeniclus) in the southeastern part of the Canton Zurich (Switzerland), from which local declines of this species have been reported. Here, wetlands are as small as 2.7 ha and separated through intensively used agricultural landscapes. Demographic data consisted of dispersal of colour-banded individuals among subpopulations, immigration rates and extinction-/recolonization dynamics. Genetic data were based on the distribution of genetic variability and gene flow among subpopulations derived from the analysis of nine microsatellite loci. Both demographic and genetic data revealed that the patchy population model best described the spatial organization of reed bunting subpopulations. High levels of dispersal among subpopulations, high immigration into the patchy population, and genetic admixture suggested little risk of extinction of both subpopulations and the entire patchy population. This study exemplifies the idea that spatially discrete subpopulations may be organized in ways other than a metapopulation, and hence has implications for the conservation of subpopulations and species. AbstractSpecies often occur in subdivided populations as a consequence of spatial heterogeneity of the habitat. To describe the spatial organization of subpopulations, existing theory proposes three main population models, which predict different levels of connectivity among and extinction risks of subpopulations: patchy population, metapopulation and isolated populations. However, spatially discrete subpopulations are commonly considered to be organized as metapopulations, although explicit tests of metapopulation assumptions are rare.Here, we test predictions of the three models on the basis of demographic and genetic data, a combined approach so far surprisingly little used in mobile organisms. This study exemplifies that spatially discrete subpopulations may be organized in ways other than a metapopulation, which has implications for the conservation of subpopulations and species.Patchy population structure in Reed buntings 3
In recent decades, female red-cockaded woodpeckers (Picoides borealis) have laid eggs increasingly earlier in response to a changing climate, as has been observed in several other bird species breeding at north temperate latitudes. Within each year, females that lay earlier are more productive than females that lay later. However, inexperienced females, experienced females who change mates and inbred birds have not adjusted to the changing climate by laying earlier, and have suffered reproductive costs as a result. Failure to respond to global climate change may be a further example of the reduced ability of inbred animals to respond to environmental challenges.
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