Data from: Functional trait differences and trait plasticity mediate biotic resistance to potential plant invaders

1. Biotic resistance represents an important natural barrier to potential
invaders throughout the world, yet the underlying mechanisms that drive
such resistance are still debated. In theory, native communities should
repel both functionally similar invaders which compete for the same
resources, and invaders which possess less competitive traits. However,
environmental stress, trade-offs across vital rates and
competition-induced plastic trait shifts may modify expected competitive
outcomes, thereby influencing invasion dynamics. 2. In order to test these
theoretical links between trait distributions and biotic resistance, we
performed a mesocosm experiment with 25 non-native ornamental species
invading native plant communities. Each non-native species was grown with
and without the native community under two watering treatments (regular
and reduced). We measured biotic resistance as the difference in
performance of non-native individuals grown with and without the community
in terms of their survival, growth and reproduction. We quantified overall
functional dissimilarity between non-native ornamental individuals and
native communities based on the combination of plant height, specific leaf
area and seed mass. Then, assuming each of these traits is also
potentially linked to competitive ability, we measured the position of
non-natives on trait hierarchies. While height is positively correlated
with competitive ability for light interception, conservative leaf and
seed characteristics provide greater tolerance to competition for other
resources. Finally, we quantified plastic trait shifts of non-native
individuals induced by competition. 3. Indeed, the native community
repelled functionally similar individuals by lowering their survival rate.
Simultaneously, shorter ornamental individuals with larger specific leaf
areas were less tolerant to biotic resistance from the community across
vital rates, although the effect of trait hierarchies often depended on
watering conditions. Finally, non-natives responded to competition by
shifting their traits. Most importantly, individuals with more competitive
traits were able to overcome biotic resistance also through
competition-induced plastic trait shifts. 4. Synthesis. Our results
highlight that both functional dissimilarity and trait hierarchies mediate
biotic resistance to ornamental plant invaders. Nevertheless,
environmental stress as well as opposing trends across vital rates are
also influential. Furthermore, plastic trait shifts can reinforce
potential invaders’ competitive superiority, determining a positive
feedback.