Geographical variation in diaspore traits of an ant-dispersed plant (Helleborus foetidus): are ant community composition and diaspore traits correlated?

Abstract

1 We explored geographical variation in the interaction between the elaiosome-bearing seeds of Helleborus foetidus and ant dispersers. We looked for correlation across nine Iberian localities, between diaspore traits and structural and functional characteristics of ant communities. 2 Mean diaspore traits did not show a distance-dependent pattern. Seed size-related traits (length, width, diaspore mass and seed mass) varied mostly among localities and ant reward-related traits (elaiosome mass and elaiosome to seed mass ratio) mainly within plants. 3 Ant communities showed distance-dependent patterns in composition and abund- ance. Almost all ant species responded positively to diaspore offerings and preferred seeds with elaiosomes. The extent of the preference differed among species and was affected by ant size. Ant size was however, similar in almost all localities and the quality of the disperser guild, estimated as the ant response to seed offerings, did not vary. 4 We found a large-scale lack of adjustment: seed traits could not be predicted from ant community composition or geographical distance. Nor could structural and functional ant community parameters explain variation in seed traits. 5 Comparison of ant sizes, position on a Principal Components Analysis of seed traits, and indirect estimates of dispersal success, suggests that there is a mosaic of well- matched and mismatched situations which probably obscures the overall relationships among seed traits and ant assemblages. This is consistent with the role proposed for the geographical structure of interactions in recent coevolutionary theories.