Trade‐offs in non‐native plant herbivore defences enhance performance

Abstract

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.

Assessment of leaf defense hypotheses at the intraspecific scale in three Helianthus (Asteraceae) species1

“…Across genotypes of the tall goldenrod Solidago altissima, those with artificially higher nutrient levels had lower constitutive plant defenses, but increased induced resistance after experimental exposure to herbivory (Burghardt 2016). Differences between constitutive and induced defenses could also be important, as they may represent different responses to herbivore pressures (energetic tradeoffs versus plastic responses) (Sun et al 2023). Although we did not measure induced defenses in this study, experimental treatments could be applied to observe if this pattern can be replicated in sunflowers.…”