Trends in weather conditions favor generalist over specialist species in rear‐edge alpine bird communities

Abstract

AbstractRear‐edge alpine biodiversity is expected to suffer one of the largest ecological impacts due to current and foreseen climate change. For highly mobile and long‐living species, climate change might operate through a wide spectrum of demographic and ecological processes influencing population dynamics, which in turn affect local abundance and may eventually lead to population extinctions and drifts in the actual range. Using the community of six passerine species breeding in the alpine zone of the Cantabrian mountains (Northwest Iberian Peninsula), we sought to document the changes in bird abundance across the elevational gradient during the last decade, evaluate the relationship between bird abundance and local climatic conditions (i.e., weather conditions), and discuss the mechanisms by which these conditions might be mediating the observed abundance trends in a global warming context. We estimated bird abundance at the home range level using point count transects and distance sampling during the breeding season, and fitted generalized linear mixed models to describe their temporal trends across the elevational gradient. We used a structural equation modeling approach to estimate the direct, indirect, and total effects of weather and temporal variables, while considering the correlations and causal relationships among them and with the elevational gradient. We found that generalist species had an overall positive trend in their abundance, while alpine specialist had a negative trend at the highest elevations during the study period. This pattern was partly explained by the decrease in wind speed and rising temperature during the study period, which seems to have a stronger effect on abundance of specialist species at the highest elevations in this rear‐edge alpine bird community. The effects of weather conditions on the abundance of different bird species in alpine ecosystems seem to be mainly related to the capacity of weather to modulate variations in habitat quality and feeding resources across the elevational gradient. Thus, in a global warming context, it is necessary to gain knowledge of the ecological processes modulating population dynamics of alpine specialists and delineate habitat conservation practices to safeguard alpine biodiversity.