Data from: Regional diversity reverses the negative impacts of an alien predator on local species-poor communities

Species diversity is often an implicit source of biological insurance for
communities against the impacts of novel perturbations, such as the
introduction of an invasive species. High environmental heterogeneity
(e.g., a mountainous gradient) is expected to beget greater regional
species diversity and variation in functional traits related to
environmental tolerances. Thus, heterogeneous metacommunities are expected
to provide more tolerant colonists that buffer stressed local communities
in the absence of dispersal limitation. We tested the hypothesis that
importation of a regional zooplankton pool assembled from a diverse array
of lakes and ponds lessens the impacts of a novel predator on local
species-poor alpine communities by increasing response diversity (i.e.,
diversity of tolerances to environmental change) as mediated by variation
in functional traits related to predator evasion. We also tested if
impacts varied with temperature, as warming may modify (e.g., dampen or
amplify) invasion effects. An eight-week factorial experiment ([fishless
vs. introduced Oncorhynchus mykiss (rainbow trout)] x [ambient temperature
vs. heated] x [local vs. local + regional species pool]) was conducted
using thirty-two 1000 L mesocosms. Associations between experimental
treatments and species functional traits were tested by RLQ and
fourth-corner analyses. Although the introduced predator suppressed local
species richness and community biomass, colonization by several montane
zooplankters reversed these negative effects, resulting in increased
species diversity and production. Invasion resistance was unaffected by
higher temperatures, which failed to elicit any significance impacts on
the community. We discovered that the smaller body sizes of imported
species drove functional overcompensation (i.e., increased production) in
invaded communities. The observed ecological surprise showed how
regionally sourced biodiversity from a highly heterogeneous landscape can
offset, and even reverse, the local negative impacts of an invasive
species. Further, prey body size was found to be a key species trait
mediating the ecological impacts of the aquatic invasive predator. Our
study highlights the novel application of a functional approach to
understanding the impacts of biological invasions, using species traits
that pertain directly to potential responses to exotic species.