Data from: Does natural variation in diversity affect biotic resistance?

1. Theories linking diversity to ecosystem function have been challenged
by the widespread observation of more exotic species in more diverse
native communities. Few studies have addressed the key underlying process
by dissecting how community diversity is shaped by the same environmental
gradients that determine biotic and abiotic resistance to new invaders. 2.
In grasslands on highly heterogeneous soils, we used addition of a recent
invader, competitor removal, and structural equation modelling (SEM) to
analyse soil influences on community diversity, biotic and abiotic
resistance, and invader success. 3. Biotic resistance, measured by
reduction in invader success in the presence of the resident community,
was negatively correlated with species richness and functional diversity.
However, in the multivariate SEM framework, biotic resistance was
independent of all forms of diversity, and was positively affected by soil
fertility via community biomass. Abiotic resistance, measured by invader
success in the absence of the resident community, peaked on infertile
soils with low biomass and high community diversity. Net invader success
was determined by biotic resistance, consistent with this invader's
better performance on infertile soils in unmanipulated conditions. 4. Seed
predation added slightly to biotic resistance without qualitatively
changing the results. Soil-related genotypic variation in the invader also
did not affect the results. 5. Synthesis In natural systems, diversity may
be correlated with invasibility and yet have no effect on either biotic or
abiotic resistance to invasion. More generally, the environmental causes
of variation in diversity should not be overlooked when considering the
potential functional consequences of diversity.