Data from: Disentangling the processes driving plant assemblages in mountain grasslands across spatial scales and environmental gradients

Habitat filtering and limiting similarity are well‐documented ecological
assembly processes that hierarchically filter species across spatial
scales, from a regional pool to local assemblages. However, information on
the effects of fine‐scale spatial partitioning of species, working as an
additional mechanism of coexistence, on community patterns is much
scarcer. In this study, we quantified the importance of fine‐scale spatial
partitioning, relative to habitat filtering and limiting similarity in
structuring grassland communities in the western Swiss Alps. To do so, 298
vegetation plots (2 m × 2 m) each with five nested subplots (20 cm × 20
cm) were used for trait‐based assembly tests (i.e., comparisons with
several alternative null expectations), examining the observed plot and
subplot level α‐diversity (indicating habitat filtering and limiting
similarity) and the among‐subplot β‐diversity of traits (indicating
fine‐scale spatial partitioning). We further assessed variations in the
detected signatures of these assembly processes along a set of
environmental gradients. We found habitat filtering was the dominating
assembly process at the plot level with diminished effect at the subplot
level, whereas limiting similarity prevailed at the subplot level with
weaker average effect at the plot level. Plot‐level limiting similarity
was positively correlated with fine‐scale partitioning, suggesting that
the trait divergence resulted from a combination of competitive exclusion
between functionally similar species and environmental
micro‐heterogeneities. Overall, signatures of assembly processes only
marginally changed along environmental gradients, but the observed trends
were more prominent at the plot than at the subplot scale. Synthesis. Our
study emphasises the importance of considering multiple assembly processes
and traits simultaneously across spatial scales and environmental
gradients to understand the complex drivers of plant community
composition.