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.

Non‐native plants are typically released from specialist enemies but continue to be attacked by generalists, albeit at lower intensities. This reduced herbivory may lead to less investment in constitutive defences and greater investment in induced defences, potentially reducing defence costs. We compared herbivory on 27 non‐native and 59 native species in the field and conducted bioassays and chemical analyses on 12 pairs of non‐native and native congeners. Non‐natives suffered less damage and had weaker constitutive defences, but stronger induced defences than natives. For non‐natives, the strength of constitutive defences was correlated with the intensity of herbivory experienced, whereas induced defences showed the reverse. Investment in induced defences correlated positively with growth, suggesting a novel mechanism for the evolution of increased competitive ability. To our knowledge, these are the first linkages reported among trade‐offs in plant defences related to the intensity of herbivory, allocation to constitutive versus induced defences, and growth.

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