Context Dependency of Biotic Interactions and Its Relation to Plant Rarity

Aim Biotic interactions can determine rarity and commonness of species, however, evidence that rare and common species respond differently to biotic stress is scarce. This is because biotic interactions are notoriously context dependent and traits leading to success in one habitat might be costly or unimportant in another. We aim to identify plant characteristics that are related to biotic interactions and may drive patterns of rarity and commonness, taking environmental context into account. Location Switzerland. Methods In a multispecies experiment, we compared the response to biotic interactions of 19 rare and 21 widespread congeneric plant species in Switzerland, while also accounting for variation in environmental conditions of the species' origin. Results Our results restrict the long-standing hypothesis that widespread species are superior competitors to rare species to only those species originating from resource-rich habitats, in which competition is usually strong. Tolerance to herbivory and ambient herbivore damage, on the other hand, did not differ between widespread and rare species. In accordance with the resource-availability hypothesis, widespread species from resource-rich habitats where more damaged by herbivores (less defended) than widespread species from resource-poor habitats-such a growth-defence trade-off was lacking in rare species. This indicates that the evolutionary important trade-off between traits increasing competitive ability and defence is present in widespread species but may have been lost or never evolved in rare species. Main conclusions Our results indicate that biotic interactions, above all competition, might indeed set range limits and underlines the importance of including context dependency in studies comparing traits of common and rare or invasive and non-invasive species.