Data and code from "A dimmer shade of pale: revealing the faint signature of local assembly processes on the structure of strongly filtered plant communities"

Trait-based ecology suggests that abiotic filtering is the main mechanism
structuring the regional species pool in different subsets of
habitat-specific species. At more local spatial scales, other ecological
processes may add on giving rise to complex patterns of functional
diversity (FD). Understanding how assembly processes operating on the
habitat-specific species pools produce the locally observed plant
assemblages is an ongoing challenge. Here, we evaluated the importance of
different processes to community assembly in an alpine fellfield,
assessing its effects on local plant trait FD. Using classical
randomization tests and linear mixed models, we compared the observed FD
with expectations from three null models that hierarchically incorporate
additional assembly constraints: stochastic null models (random assembly),
independence null models (each species responding individual and
independently to abiotic environment), and co-occurrence null models
(species responding to environmental variation and to the presence of
other species). We sampled species composition in 115 quadrats across 24
locations in the central Pyrenees (Spain) that differed in soil
conditions, solar radiation and elevation. Overall, the classical
randomization tests were unable to find differences between the observed
and expected functional patterns, suggesting that the strong abiotic
filters that sort out the flora of extreme regional environments blur any
signal of other local processes. However, our approach based on linear
mixed models revealed the signature of different ecological processes. In
the case of seed mass and leaf thickness, observed FD significantly
deviated from the expectations of the stochastic model, suggesting that
fine-scale abiotic filtering and facilitation can be behind these
patterns. Our study highlights how the hierarchical incorporation of
ecological additional constraints may shed light on the dim signal left by
local assembly processes in alpine environments.