Karin Schiegg

Genetic and Environmental Influences on Natal Dispersal Distance in a Resident Bird Species

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.

Ecological and social effects on reproduction and local recruitment in the red-backed shrike

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.

Inbreeding and experience affect response to climate change by endangered woodpeckers

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.

Patchy population structure in a short-distance migrant: evidence from genetic and demographic data.

Species 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: 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.

Environmental autocorrelation: curse or blessing?

Theory of population dynamics predicts that environmental autocorrelation increases extinction risk. Recent work by Engen and colleagues confirms this and demonstrates how the spatial extent of population synchrony is influenced by dispersal. However, in a new study, Gonzalez and Holt demonstrate that environmental autocorrelation causes substantial increases in the size of populations with negative growth rates, provided that they are sustained by immigrating dispersers. These new findings could change our view of dispersal and sink populations, whilst providing an explanation for previously enigmatic population outbreaks.

TESTING A SPATIALLY EXPLICIT, INDIVIDUAL-BASED MODEL OF RED-COCKADED WOODPECKER POPULATION DYNAMICS

Stochastic population models are widely used to assess extinction risk under various management scenarios, but due to the lack of independent data, such models are tested only rarely. Here we evaluate the predictive accuracy of a stochastic, spatially explicit, individual-based model of the population dynamics of the Red-cockaded Woodpecker by comparing simulated data with independent empirical data sets from two populations. We examined primary model predictions such as population size and number of territories, and secondary predictions such as population structure, dispersal success, natal dispersal dis- tances, and age distributions. The model predicted most evaluated parameters with high accuracy, but model performance could be enhanced by including pioneering behavior and by improving estimates of male and female dispersal behavior. We judge our model to provide reliable predictions when applied to real populations, with a few specific exceptions.

PERMANENT GENETIC RESOURCES: Isolation, characterization and multiplex genotyping of 11 autosomal and four sex-linked microsatellite loci in the reed bunting, Emberiza schoeniclus (Emberizidae, Aves)

Fifteen highly polymorphic microsatellite loci were characterized in the reed bunting, Emberiza schoeniclus. Eleven loci were autosomal and four linked to the Z chromosome. All loci were characterized and tested in 45 unrelated reed buntings from a Swiss population. Autosomal loci displayed seven to 17 and sex‐linked loci displayed four to 13 alleles with heterozygosities ranging from 0.756 to 0.933 and from 0.478 to 0.957, respectively. These loci will be used in population genetic and mating system studies of reed buntings.

Sources, Sinks and Sustainability: Source–sink status of small and large wetland fragments and growth rate of a population network

Many organisms persist in populations that are spatially structured by human-induced loss and fragmentation of their native habitats. Despite this, the demographic contributions of local populations to a population network and to the growth rate of such a network are still largely unexplored. Using data on individually marked young and adult female reed buntings ( Emberiza schoeniclus ) from 21 local populations studied over six years in northeastern Switzerland , we examined the source—sink status of small and large local populations with recently developed metrics. We hypothesized that including emigration to the population network (the C r metric) would classify more local populations as sources than when only focusing on the ability of local populations to maintain themselves (the Rr metric). We further tested the hypothesis that the relative contribution of small and large local populations to the population network does not differ. The inclusion of emigration to the population network resulted in significantly higher values than when only considering the contribution of local populations to themselves, the difference between the metrics averaging 30%. Despite this, most local populations in our study turned out to be sinks (C r value <1), suggesting that substantial immigration is required for maintaining local populations as well as the entire population network (growth rate of network always <1). Both large and small populations contributed equally to the population network. We conclude that (a) the source—sink status of local populations is more comprehensively described by metrics including emigration (such as C r ) than by metrics focusing on processes within local populations (such as Rr ); (b) the network of local populations studied here is not viable without immigration; and (c) small local populations can be as valuable as large local populations in their contribution to a population network.