Context dependency of biotic interactions and its relation to plant rarity

Abstract 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 multi-species 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 to 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-defense tradeoff was
lacking in rare species. This indicates that the evolutionary important
tradeoff 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.