Density‐dependent fitness, not dispersal movements, drives temporal variation in spatial genetic structure in dark‐eyed juncos (Junco hyemalis)

Abstract

Some studies have found that dispersal rates and distances increase with density, indicating that density‐dependent dispersal likely affects spatial genetic structure. In an 11‐year mark–recapture study on a passerine, the dark‐eyed junco, we tested whether density affected dispersal distance and/or fine‐scale spatial genetic structure. Contrary to expectations, we found no effect of predispersal density on dispersal distance or the proportion of locally produced juveniles returning to the population from which they hatched. However, even though density did not affect dispersal distance or natal return rates, we found that density still did affect spatial genetic structure. We found significant positive spatial genetic structure at low densities of (postdispersal) adults but not at high densities. In years with high postdispersal (adult) densities that also had high predispersal (juvenile) densities in the previous year, we found negative spatial genetic structure, indicating high levels of dispersal. We found that density also affected fitness of recruits, and fitness of immigrants, potentially linking these population parameters with the spatial genetic structure detected. Immigrants and recruits rarely nested in low postdispersal density years. In contrast, in years with high postdispersal density, recruits were common and immigrants had equal success to local birds, so novel genotypes diluted the gene pool and effectively eliminated positive spatial genetic structure. In relation to fine‐scale spatial genetic structure, fitness of immigrants and new recruits is poorly understood compared to dispersal movements, but we conclude that it can have implications for the spatial distribution of genotypes in populations.

Application of stable isotopes to study movement ecology and diet variation in a migratory songbird

“…It is found breeding and molting in the northern regions of Canada and Alaska, and mountainous regions of the United States (U.S.) and wintering in the lower latitudes of Canada and the majority of the continental U.S. and northern Mexico (Nolan et al, 2002). This species has shown negative population trends of over 40% in some areas in the last decade (PIF 2017;Rockwell et al, 2019) and its physiology and migratory behaviors have been the focus of numerous studies (Nolan and Ketterson, 1983;Rogers et al, 1994.;Fudickar et al, 2016;Liebgold et al, 2019). Bridge et al (2010) analyzed hydrogen isotope ratios from secondary feathers in a population of Dark-eyed Juncos, all from the same hyemalis subspecies group (slate-colored), sampled during the winter of 2009 in central Oklahoma (U.S.) and showed isotopic variation ranging from -175.6‰ to -118.6‰ from Vienna Standard Mean Ocean Water (VSMOW).…”

“…This species has shown negative population trends of over 40% in some areas in the last decade (PIF 2017; Rockwell et al, 2019) and its physiology and migratory behaviors have been the focus of numerous studies (Nolan and Ketterson, 1983; Rogers et al, 1994. ; Fudickar et al, 2016; Liebgold et al, 2019).…”