DOI: 10.5061/dryad.d45jj19
title: Data from: Disentangling the effects of multiple environmental drivers on population changes within communities

description: 1. The effects of different environmental drivers on the changes in
 species’ population abundances can be difficult to disentangle since they
 often act simultaneously. Researchers have built statistical models that
 include environmental variables (such as annual temperature), or species
 attributes (such as a species’ temperature preference), which are assumed
 to detect the impacts of specific drivers (such as climate change).
 However, these approaches are often applied separately or, if combined,
 not explicitly compared. 2. We show the complementary insights gained by
 applying both these approaches to a community dataset on Danish
 terrestrial birds. We use our analysis to compare the relative importance
 of climate change and agricultural land-use change for the abundance
 changes within the community between 1983 and 2013. 3. Population models
 were fitted to the community data of species’ annual abundances with
 predictors comprising: species attributes (species’ temperature and
 habitat preferences), environmental variables (climatic and agricultural
 land-use change variables), or both. Relationships between species’
 abundances and environmental variables were used to identify the drivers
 associated with average abundance changes of species in the community.
 Relationships between species’ abundances and their attributes were used
 to understand the drivers causing interspecific variation in abundance
 changes.4. Warmer winters were positively associated with community-level
 abundances, and warm-adapted species had more positive abundance changes
 than cold-adapted ones. Agricultural land-use area was negatively
 associated with community-level abundances, and birds using a high
 proportion of meadow and habitat specialists had more negative abundance
 changes than birds using other habitats and habitat generalists. Effect
 sizes of environmental variables were larger for agricultural land-use
 change while those for species attributes were larger for climate change.
 5. The environmental-data approach suggested that agricultural land-use
 change has decreased the average abundances of species in the community,
 affecting total community size while the species-attribute based approach
 suggested that climate change has caused variation in abundance among
 species, affecting community composition. Environmental variables and
 species attributes that are hypothesized to link to specific drivers can
 be used together to provide complementary information on the impacts of
 different drivers on communities.
description: SOM_data_file_1_ynglefugle_index_og_standard_errorThese indices are based on annual point count surveys that now involves c. 370 routes across the country monitored in the period 1st May – 15th June (Nyegaard et al. 2015). Most routes consist of 10–20 marked ‘points’ at which all birds seen and heard are recorded in a 5-min observation period (Heldbjerg 2005). All routes are counted in at least two years by the same observer, at the same time of year (± 7 days), same time of day (± 30 min) and under good weather conditions. The annual national abundance indices for each species had been calculated by DOF-Birdlife Denmark by fitting a log linear regression model to the point count data with Poisson error terms using the software TRends and Indices for Monitoring data (TRIM) (Pannekoek & van Strien 2004).The most up-to-date data files can be found on their website (http://www.dof.dk). For further details, see: See Nyegaard, T., Larsen, J.D., Brandtberg, N. & Jørgensen, M.F. (2015) Common bird Census in Denmark 1975-2014. Dansk Ornitologisk Forening (in Danish, with English summary).