Does a history of population co-occurrence predict plant performance, community productivity, or invasion resistance?

A history of species co-occurrence in plant communities is hypothesized to
lead to greater niche differentiation, more efficient resource
partitioning, and more productive, resistant communities as a result of
evolution in response to biotic interactions. A similar question can be
asked of co-occurring populations: do individual species or community
responses differ when communities are founded with plants sharing a
history of population co-occurrence (sympatric) or originating from
different locations (allopatric)? Using shrub, grass, and forb species
from six locations in the western Great Basin, USA, we compared
establishment, productivity, reproduction, phenology, and resistance to
invaders for experimental communities with either sympatric or allopatric
population associations. Each community type was planted with six taxa in
outdoor mesocosms, measured over three growing seasons, and invaded with
the annual grass Bromus tectorum in the final season. For most
populations, the allopatric or sympatric status of neighbors was not
important. However, in some cases, it was beneficial for some species from
some locations to be planted with allopatric neighbors, while others
benefited from sympatric neighbors, and some of these responses had large
effects. For instance, the Elymus population that benefited the most from
allopatry grew 50% larger with allopatric neighbors than in single origin
mesocosms. This response affected invasion resistance, as B. tectorum
biomass was strongly affected by productivity and phenology of Elymus
spp., as well as Poa secunda. Our results demonstrate that while community
composition can affect plant performance in semi-arid plant communities,
assembling communities from sympatric populations is not sufficient to
ensure high productivity and invasion resistance. Instead, we observed an
idiosyncratic interaction between sampling effects and evolutionary
history, with the potential for seed source of individual populations to
have community-level effects.