Journal Article

Sympatry leads to reduced body condition in chickadees that occasionally hybridize

Burg, Theresa M., Otter, Ken A., Grabenstein, Kathryn C., Taylor, Scott A.

2022

Overview

Both abiotic and biotic drivers influence species distributions. Abiotic drivers such as climate have received considerable attention, even though biotic drivers such as hybridization often interact with abiotic drivers. We sought to explore the (1) costs of co‐occurrence for ecologically similar species that hybridize and (2) associations between ecological factors and condition to understand how abiotic and biotic factors influence species distributions. For two closely related and ecologically similar songbirds, black‐capped and mountain chickadees, we characterized body condition, as a proxy for fitness, using a 1358‐individual range‐wide dataset. We compared body condition in sympatry and allopatry with several abiotic and biotic factors using species‐specific generalized linear mixed models. We generated genomic data for a subset of 217 individuals to determine the extent of hybridization‐driven admixture in our dataset. Within this data subset, we found that ~11% of the chickadees had hybrid ancestry, and all hybrid individuals had typical black‐capped chickadee plumage. In the full dataset, we found that birds of both species, independent of demographic and abiotic factors, had significantly lower body condition when occurring in sympatry than birds in allopatry. This could be driven by either the inclusion of cryptic, likely poor condition, hybrids in our full dataset, competitive interactions in sympatry, or range edge effects. We are currently unable to discriminate between these mechanisms. Our findings have implications for mountain chickadees in particular, which will encounter more black‐capped chickadees as black‐capped chickadee ranges shift upslope and could lead to local declines in mountain chickadee populations. Understanding how species are distributed across landscapes, the relative influence of abiotic and biotic factors, and the consequences of overlap, is a central goal of evolutionary ecology, especially as ranges shift in response to rapid global change. We compared body condition between black‐capped and mountain chickadees in sympatry and allopatry to several demographic factors of known importance, as well as to abiotic factors, and controlled for hybrid status in a subset of the data using genome‐spanning loci. We found that, for both species, birds in sympatry, regardless of sex or age, had significantly lower body condition than birds in allopatry, and that this pattern might be driven by either the inclusion of cryptic, likely poor condition, hybrids in our full dataset, competitive interactions in sympatry, or range edge effects.

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc,Wiley
• Subject: Abiotic factors / Admixtures / Allopatry / Animal reproduction / Biogeography / Biotic factors / body condition / Datasets / Ecological effects / Ecology / Edge effect / Females / Genomics / Habitats / Hybridization / Hybrids / Influence / interspecific competition / Males / Morphology / Mountains / Plumage / Precipitation / range edges / skyward contractions / Songbirds / Spatial Ecology / Species / species distributions / Statistical models / Sympatry