DOI: 10.5061/dryad.h18931zjw
title: Bird communities in the Swiss Alps, 1999-2018, abundance data

description: Aim: Mountains are biodiversity hotspots and are among the most
 sensitive eco- systems to ongoing global change being thus of conservation
 concern. Under this scenario, assessing how biological communities vary
 over time along elevational gra- dients and the relative effects of
 niche-based deterministic processes and stochastic events in structuring
 assemblages is essential. Here, we examined how the temporal trends of
 bird communities vary with elevation over a 20 year-period (1999–2018). We
 also tested for differences in temporal dynamics among habitat types
 (among-community variability) and functional groups (within-community
 variability). Taxon: 97 species of common breeding birds.
 Location: Swiss Alps. Methods: We used abundance data
 from the Swiss breeding bird survey to compute different temporal dynamic
 metrics (temporal turnover, synchrony, rate of community change and
 community-level of covariance among species). We also examined the
 relative contribution of deterministic and stochastic processes in
 community assembly using the Raup-Crick method and the normalized
 stochasticity ratio. Results: We found that, with
 greater elevation, temporal species turnover increased while the rate of
 overall community change over successive years decreased, suggesting that
 high-elevation communities display more erratic dynamics with no clear
 trend. Despite this, we found a more deterministic assembly of alpine
 communities in comparison to those located at lower elevations.
 Deterministic processes had greater influence than stochastic processes on
 community assembly along the entire elevational gradient (80% of
 communities). Forest communities exhibited higher synchrony in comparison
 to the remaining habitats likely because they consisted of species with
 greater functional redundancy, whereas alpine communities were the least
 stable as a result of their low taxonomic richness (‘portfolio’ effect).
 Main conclusions: Community-level synchrony was overall positive
 supporting the idea that compensatory mechanisms are rare in natural
 biological communities. Our results suggest that rather than competition,
 the existence of differences in the eco-logical strategies of species may
 have a stabilizing effect on bird communities by weakening the concordance
 of species responses to fluctuations in environmental conditions
 (i.e. enhanced interspecific temporal asynchrony). This study provides
 evidence that, although species turnover in metacommunities is frequent, a
 high tem- poral turnover does not necessarily imply the overriding
 importance of stochastic processes.
description: Relative abundance data (number of territories per site)
 collected during two decades (period 1999-2018) in 131 plots along
 a ~2,300 m elevational gradient (range: 380–2,710 m) in the Swiss Alps. A
 total of 97 common species (one columen per species) were considered in
 this study. The first two columns indicate plot ID and study year,
 respectively. 
description: Data comes from the ‘Monitoring HäufigeBrutvögel’ (MHB) scheme,
 a volunteer-based programme aimed at annual monitoring of population
 dynamics of common breeding species in Switzerland. This program is
 coordinated by the Swiss Ornithological Institute
 (www.vogelwarte.ch).