DOI: 10.5061/dryad.7wm37pvtr
title: Partitioning beta diversity to untangle mechanisms underlying the assembly of bird communities in Mediterranean olive groves

description: Aim: We investigated taxonomic and functional beta diversity of bird
 communities inhabiting Mediterranean olive groves subject to either
 intensive or extensive management of the ground cover and located in
 landscapes with different degrees of complexity. Location: Andalusia,
 southern Spain. Methods: We partitioned taxonomic and functional beta
 diversity into its two additive components, turnover and nestedness. We
 also explored the contributions of single sites to overall beta diversity
 (LCBD) and separated the effects of species replacement (turnover) and
 richness difference (nestedness) in order to identify ecologically unique
 sites -keystone communities- within the metacommunity. In a further step,
 we employed abundance- and functional-based indicator species analyses to
 characterize bird assemblages.  Results: Taxonomic beta diversity
 increased with landscape complexity. Although both taxonomic and
 functional differences among assemblages were driven mainly by species
 replacement (regardless of management or landscape type), the contribution
 of trait replacement to the total functional beta diversity was much
 lower, suggesting that species performing similar functions replace each
 other between sites. There were no differences in LCBD between management
 types or categories of landscape complexity, but the contributions of
 sites to beta diversity decreased as the percentage cover of olive groves
 increased. Species richness was also important in explaining variation in
 LCBD as species-poor sites tended to contribute the most to the
 local-to-regional beta diversity. However, some farms displayed high
 values of LCBD due to the existence of a high replacement component,
 indicating that some species recorded in these sites were scarce
 elsewhere. The indicator species analyses revealed that the woodchat
 shrike Lanius senator may constitute an excellent
 indicator of biodiversity in this agro-forestry-system.  Main
 conclusions: Our results show that agricultural expansion
 promotes biotic homogenization and exemplify how the identification of
 both keystone species and communities can represent a powerful tool for
 the management of anthropized landscapes.
description: Bird censuses carried out in the framework of the LIFE project
 'Olivares Vivos' (https://olivaresvivos.com)
 Surveys were conducted using point census stations. At each count
 point, all individuals detected -seen or heard- within a 100-m radius were
 identified and counted for 5 min. We set six stations
 in small olive farms (&lt;25 ha) and 10 in large olive farms
 (&gt;25 ha). To avoid repeated counts between neighbor census
 stations, they were located at least 200 m apart in small olive groves and
 at least 300 m apart in large olive groves. Surveys were carried out
 monthly in two slots (from April to June 2016, and from September 2016 to
 March 2017) under favorable weather conditions by a team of skilled
 ornithologists.  Monthly data (abundances) were merged
 into a single plot x species quantitative matrix used as input in
 beta-diversity analyses.  
description: Bird abundance data (97 species) for each olive farm (plot). Each
 farm is catalogued according to the level of landscape complexity (high;
 intermediate; low) and the type of management of the ground cover
 (extensive or intensive).