Data from: Along with intraspecific functional trait variation, individual performance is key to resolving community assembly processes

Species contributing high proportions to community biomass strongly
influence ecosystem processes within the community. Studies have shown
that dominant species may serve as nurse plants, helping to ensure biomass
stability of the subordinate species under stress conditions. The question
is widely debated as to whether either niche differentiation or neutral
processes drive the net outcome of plant interactions within a subordinate
plant community. To answer this question, requires precise estimates of
individual variation in functional traits and performance. In a five-year
mesocosm experiment, the functional responses of a subordinate plant
community to the removal of the dominant species were evaluated across two
drought-stress scenarios. Small scale (i.e., large pots) wetland
communities were constructed comprising one dominant species (Carex elata)
and three subordinate species. Removal of the dominant species allowed
evaluation of the net effects of drought and interspecific interactions.
We estimated the functional divergences for three traits (specific leaf
area, leaf dry matter content and height growth allocation) and compared
these with performance differences quantified individually. This enabled
distinctions to be made between deterministic (i.e., niche
differentiation) and neutral processes driving the drought response of the
subordinate community. We showed that the dominant species decreased
relative performance differences within the subordinate plant community
under conditions of permanent drought stress. These changes were
associated with the convergence of traits related to resource acquisition
and growth. The dominant species equalised species performance differences
by supressing relatively drought-tolerant species with low competitive
ability and by supporting the less drought-tolerant species with
relatively high competitive ability. Meanwhile, under conditions of
interannual drought, the subordinate species likely coexisted due to
differentiation in resource-use strategies and the interaction with the
dominant species. Inclusion of individual variation in performance with a
functional trait approach provides valuable insights into the processes
structuring plant communities. Ours is the first study to provide evidence
that subordinate species exposed to drought may coexist via neutral
processes arising from their interactions with the dominant species,
leading to functional convergence of traits associated with the trade-off
between stress tolerance and competitive ability.