The relationships among developmental stability, canalization and phenotypic plasticity are not straightforward, but may be better understood in the context of temporally heterogeneous environments. Our objective was to investigate the effects of early experience with temporally heterogeneous water availability on the associations between developmental stability, canalization and phenotypic plasticity. We subjected eight plant species to a first round of alternating inundation and drought vs. constantly moderate water treatments and a second round of water conditions. Fluctuating asymmetry (FA), intra- and inter-individual variation (CVintra and CVinter), and plasticity in traits were measured and correlations between variables were calculated for each species. Early temporally heterogeneous experience decreased the leaf size of half of the species, but had complex effects on leaf fluctuating asymmetry (FA) and inter-individual variation (CVinter) in traits immediately or in late conditions, with little effects on intra-individual variation (CVintra). There were several positive correlations between FA and CVinter, positive correlations between CVinter and plasticity in early treatments, but negative correlations in late treatments. Our results suggested complexity and variability in the relationships between different mechanisms. Decreased canalization may promote plastic responses in traits before or during the induction of plasticity, whereas canalization may reflect phenotypic convergence after plastic responses. Temporally heterogeneous experiences may facilitate positive correlations or attenuate negative correlations between decreased canalization and plasticity. We provide direct evidence for relationships between developmental stability, canalization and plasticity as well as the role of temporally heterogeneous environments in modifying these processes. The integrative way that plants deal with environmental variation demonstrates their ability to evolve in multiple directions via many flexible adjustments in response to varying environmental signals over a plant’s lifetime.

Non-native plants are typically released from specialist enemies in new ranges, but continue to be attacked by generalists, but whether they shift relative allocation to constitutive or induced defenses is unknown. We compared herbivory on co-occurring native and non-native species and also constitutive and induced defenses. Non-natives suffered less damage than natives and constitutive defenses of non-natives was lower than that of native congeners, whereas induced defense was the opposite. The strength of constitutive defenses for a species was correlated with the intensity of herbivory experienced, for non-natives, whereas induced defenses showed the reverse. The defenses of natives were not related to herbivory pressure. Finally, the strength of induced defenses correlated positively with growth, suggesting a novel mechanism for the evolution of increased competitive ability. These results expand our understanding of fundamental tradeoffs in constitutive and induced defenses and provide novel insight into how herbivory pressure affects defense allocation.

An important hypothesis for how plants respond to introduction to new ranges is the evolution of increased competitive ability (EICA). EICA predicts that biogeographical release from natural enemies initiates a tradeoff in which exotic species in non-native ranges become larger and more competitive, but invest less in consumer defenses, relative to populations in native ranges. This tradeoff is exceptionally complex because detecting concomitant biogeographical shifts in competitive ability and consumer defense depend upon which traits are targeted, how competition is measured, the defense chemicals quantified, whether defense chemicals do more than defend, whether “herbivory” is artificial or natural, and where consumers fall on the generalist-specialist spectrum. Previous meta-analyses have successfully identified patterns but have yet to fully disentangle this complexity. We used meta-analysis to reevaluate traditional metrics used to test EICA theory and then expanded on these metrics by partitioning competitive effect and competitive tolerance measures and testing Leaf Specific Mass in detail as a response trait. Unlike previous syntheses, our meta-analyses detected evidence consistent with the classic tradeoff inherent to EICA. Plants from non-native ranges imposed greater competitive effects than plants from native ranges and were less quantitatively defended than plants from native ranges. Our results for defense were not based on complex leaf chemistry, but instead were estimated from tannins, toughness traits, and primarily Leaf Specific Mass. Species specificity occurred but did not influence the general patterns. As for all evidence for EICA-like tradeoffs, we do not know if the biogeographical differences we found were caused by tradeoffs per se, but they are consistent with predictions derived from the overarching hypothesis. Underestimating physical leaf structure may have contributed to two decades of tepid perspectives on the tradeoffs fundamental to EICA.