Overlooked seed-dispersal modes and underestimated distances

Abstract

Long-distance seed dispersal is a crucial process determining the distribution of plant biodiversity and, therefore, of major interest in biogeography and macroecology. A recent data article on Global Ecology and Biogeography presented a database of estimated seed-dispersal distance classes for the European flora, where the classes are defined by the morphological dispersal syndrome of species associated with a single dispersal mode. We explain how this article overlooks literature on the unreliable capacity of dispersal syndromes for predicting key dispersal modes involved in long-distance seed dispersal. Consequently, the published database does not consider the possibility that individual species can naturally be dispersed through multiple modes (polychory). Most importantly, the database consistently omits seed-dispersal modes that can mediate dispersal distances several orders of magnitude longer than the mode predicted by the syndromes. This is the case of many terrestrial and aquatic plants dispersed by animals, notably ungulates and waterbirds, and that of coastal plants dispersed by the sea. We thus urge caution when using this database to model potential plant dispersal because long-distance seed dispersal is underestimated in many species.