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

Aim The main aims were to determine: i) the relative contribution of
species replacement and richness difference components to overall
taxonomic (TDβ) and functional (FDβ) beta diversity of spider communities;
ii) the degree to which TDβ and FDβ components can be explained by the
environmental or geographic predictors; iii) 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 (TDβtotal) and total functional (FDβtotal) beta diversity were
calculated, by pairwise comparisons, and partitioned into their
replacement (βrepl) and richness difference (βrich) 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 of 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 βrepl was the
dominant component contributing to 84.2% and 72.8% for TDβtotal and
FDβtotal, respectively. TDβtotal and FDβtotal (and their replacement
components) were higher between- than within-biogeographic regions.
TDβtotal and TDβrepl 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 TDβrich. The observed slopes of the regressions
of FDβtotal and FDβrepl in relation to environmental distance were slower
than the null model expectations. Main conclusions Spider’ assemblages
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.