Dispersal-mediated selection on plant height in an autochorously dispersed herb

Dispersal ability is an important fitness component in most plant species. Therefore, some phenotypic traits can be selected due to their effect on dispersal. In this study I determine the potential for dispersal-mediated selection on plant height in an autochorous plant, Erysimum mediohispanicum (Brassicaceae). Selection was quantified by selection gradients, structural equation modeling and generalized additive models. I detected significant dispersal-mediated linear selection gradient on plant height, taller plants dispersing seeds farther. Nevertheless, the generalized additive models suggest that the selection on stalk height was non linear. Indeed, it detected a threshold in the effect of stalk height on dispersal ability; plants shorter than that threshold had an extremely short dispersal, whereas plants taller than that threshold dispersed the seeds very far. Furthermore, the structural equation modeling showed that stalk height indirectly affected dispersal distance through its significant effect on one reproduction-related fitness component, taller plants having greater fecundity. Selection on E. mediohispanicum stalk height occurs through two simultaneous paths, one via producing many seeds and the other through increasing probability of dispersing them far away.