Seed dispersal interactions promoting plant invasions

Abstract

Animal dispersers in new areas are essential for many alien plants since they allow seeds movement and might promote seed germination and seedling establishment, increasing their chances of invasion. Here we review the published literature on seed dispersal of alien plant species by native and/or alien animals. We aim to answer the following questions: (i) Are interactions between alien plants and their animal dispersers evenly studied worldwide? (ii) Which are the distinctive traits (i.e. geographical origin, life form, dispersal strategy and propagule traits) of alien plants dispersed by animals? (iii) Which are the most studied groups of dispersers of alien plants around the world? (iv) Does literature provide evidence for the invasional meltdown hypothesis (alien plant-alien disperser facilitation)? (v) Which is the role of animal dispersers in the different stages of the alien plant regeneration process? Our dataset consisting of 204 articles indicates that geographical distribution of the studies was highly heterogeneous among continents, with the highest number coming from North America and the lowest from Asia and Central America. Most of the alien plants involved in dispersal studies were woody species from Asia with fleshy fruits dispersed by endozoochory. More than the half of the animal dispersers was birds, followed by mammals, ants and reptiles. The dominance of bird-dispersal interactions over other animal groups remained consistent across geographical regions. Although most of the studies involved only native dispersers, alien-alien interactions were detected, suggesting the occurrence of invasional meltdown mechanisms. Of the total reviewed articles reporting seed removal, 74% evaluated seed dispersal, but only few studies include seed germination (35.3%), seedling establishment (5.4 %) or seed predation (23.5 %). Finally, this chapter provides some research biases and directions for future studies in the area.