Taxonomic divergence and functional convergence in Iberian spider forest communities: Insights from beta diversity partitioning

Abstract Aim The main aims were to determine: (a) the relative contribution of species replacement and richness difference from components to overall taxonomic (TDβ) and functional (FDβ) beta diversity of spider communities; (b) the degree to which TDβ and FDβ components can be explained by the environmental or geographic predictors; (c) whether FDβ components were lower than expected given the underlying TDβ variation. Location This study was carried out in 22 oak forest sites across the Iberian Peninsula. The area comprises two biogeographic regions, Eurosiberian (North) and Mediterranean (Centre and South). Methods Spiders were sampled using a standardized protocol. A species x traits matrix was constructed. Total taxonomic (TDβ total ) and total functional (FDβ total ) beta diversity were calculated, by pairwise comparisons, and partitioned into their replacement ( β repl ) and richness difference ( β rich ) components. Mantel tests were used to relate taxonomic and functional dissimilarity with environmental and geographic distances. A spatial eigenfunction model was constructed and the variation in TDβ and FDβ explained by environment and geographic predictors was quantified. Null models were used to test if FDβ was higher or lower than expected given TDβ. Results β repl was the dominant component contributing to 84.2% and 72.8% for TDβ total and FDβ total , respectively. TDβ total and FDβ total (and their replacement components) were higher between‐ than within‐biogeographic regions. TDβ total and TDβ repl were positively correlated with environmental and geographic distances, even when controlling for a biogeographic effect, but their functional counterparts were only correlated with environmental distance. Variation partitioning showed that pure environmental and spatially structured environmental effects had a small contribution to beta diversity, except for TDβ rich . The observed slopes of the regressions of FDβ total and FDβ repl in relation to environmental distance were slower than the null model expectations. Main Conclusions Spider assemblage variation was mainly determined by the replacement, and not the net loss, of species and traits. TDβ was influenced by niche filtering and dispersal limitation, whereas FDβ was mainly generated by niche filtering. A high level of functional convergence among spider communities, despite the high taxonomic divergence, revealed the signal of replacement of species performing similar functions across sites.