Farmland bird assemblages exhibit higher functional and phylogenetic diversity than forest assemblages in France

Aim Under a global change scenario, research focused on changes in assembly patterns over spatial and temporal axes is paramount. Despite an increasing need to assess whether associations among diversity and community metrics change in relation to environmental heterogeneity, the way in which community assembly rules vary across habitats has been hardly explored. Here, we tested for differences in patterns of functional diversity (FD) and phylogenetic diversity (PD) between farmland and forest bird communities in order to improve our understanding about how biological communities respond to anthropogenic disturbances. Location Continental France. Taxon 107 species of common birds. Methods We used an extensive dataset (13 years; 7,115 bird communities) from the French Breeding Bird survey in conjunction with a matrix of 142 functional traits (including information on habitat, diet, life-stories, behaviour and morphology) to compute different metrics of FD and PD and examine how these vary between habitat types and across time. Results We found that farmland assemblages showed higher FD and PD than forest assemblages, which were phylogenetically clustered. Both FD and PD of forest assemblages increased with increasing species richness, whereas in farmland assemblages the relationship was asymptotic in both cases. This pattern may be due to the accumulation of generalists, which can end up displacing specialist species when the environment becomes oversaturated triggering a decline in diversity. Contrary to expectations, FD and PD of farmland assemblages increased over the study period, whereas forest assemblages showed a non-linear pattern. Farmland and forest assemblages also showed divergent trajectories over time in relation to FD metrics. Main conclusions Although farmland intensification led to a sharp decline in populations of farmland birds, agricultural landscapes in southern Europe still harbour diversity-rich communities probably due to the legacy effects of past land-use (traditional practices). Our study highlights the need to take into account the influence of historical landscape configurations when assessing the effect that contemporary land uses have on biotic communities.