Partitioning beta diversity to untangle mechanisms underlying the assembly of bird communities in Mediterranean olive groves

Vicente García‐Navas,Rubén Tarifa,José L Molina‐Pardo,Pedro J Rey,Teresa Salido,Carlos Martínez‐Núñez,Francisco Valera,Francisco M Camacho,John Lambrinos

doi:10.1111/ddi.13445

Abstract

AbstractAimWe investigated taxonomic and functional beta diversity of bird communities inhabiting Mediterranean olive groves subject to either intensive or low‐intensity management of the ground cover and located in landscapes with different degrees of complexity.LocationAndalusia, southern Spain.MethodsWe 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.ResultsTaxonomic 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 conclusionsOur 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.

Highlights

A major goal of ecology is to understand factors affecting the spatial variation of species diversity, which can be divided into alpha, beta and gamma components (Mittelbach & McGill, 2019)
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
We calculated multiple-site dissimilarities and components for all farms together (n = 40 farms) and for each management type and landscape complexity category separately using the beta.multi.abund function of the ‘betapart’ package (Baselga et al, 2021). Since these estimates can be influenced by α diversity, which differs among subsets, we repeated analyses of β diversity using Raup–Crick dissimilarity, an incidence-based, probabilistic metric that is not influenced by differences in species richness (Chase et al, 2011; Vellend et al, 2007)

Summary

| INTRODUCTION

A major goal of ecology is to understand factors affecting the spatial variation of species diversity, which can be divided into alpha, beta and gamma components (Mittelbach & McGill, 2019). The dominant functional traits in biological communities should provide a much better ecological characterization of a group of sites, in terms of the local environmental conditions and ecosystem functioning, than the mere occurrence of species In this way, it is feasible to determine those functional attributes that better inform about the specific properties of certain sites along natural (e.g. successional stages) or human-induced environmental gradients (e.g. land-use intensity in farmland landscapes). Landscape heterogeneity and configuration have been increasingly recognized to play an important role in structuring the composition of biological communities in agroecosystems and act synergistically with management practices or the farming system (e.g. Martins da Silva et al, 2017) Given their high dispersal capacity, bird communities inhabiting olive groves are likely to be influenced by habitats directly adjacent to crop fields (functional ‘spillover’ from natural to managed habitats; Blitzer et al, 2012). By integrating species functional characteristics and species abundances, we examined whether these environmental conditions are associated with specific functional traits (e.g. diet or foraging strategy)

| MATERIAL AND METHODS

| RESULTS

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Findings

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