Is early flowering in myrmecochorous plants an adaptation for ant dispersal?

Abstract

To analyze the extent to which early flowering of specialized myrmecochorous plants (i.e. plants producing elaiosome-bearing seeds) may be the result of adaptation for ant dispersal, we investigated flowering and fruiting patterns of common herb and shrub-layer species in a beechwood forest at the western end of the Cantabrian Range (Spain). Over the same period, we estimated ant abundance, the availability of alternative foods for ants, and the rate of removal of seeds by ants. Our results indicate: (i) that the flowering peaks of most strict myrmecochores occurred approximately 4 weeks earlier than in nonmyrmecochores; (ii) that the fruiting peak of both groups of plants occurred around the same time, in early July; (iii) that the peak in ant abundance coincides with the seed availability peak, and precedes the peak in availability of alternative ant foods; and (iv) that the probability of seed removal by Formica rufibarbis (the only ant species present in the study area) varies over the season, peaking in early July. In conclusion, our results show that despite differences in seed size, plants with ant-dispersed seeds show highly synchronous flowering, suggesting that strict myrmecochores in our study area may have adapted their phenologies to the seasonal availability of dispersers.