Ant removal distance, but not seed manipulation and deposition site increases the establishment of a myrmecochorous plant

Abstract

Myrmecochory (seed dispersal by ants) is a unique seed dispersal syndrome among invertebrates. It comprises three main phases: seed removal, seed manipulation, and seed deposition. However, the contribution of each phase to seed and seedling fate remains unclear. Here, we experimentally quantified the effects of each phase of myrmecochory on seed germination and seedling establishment, the two most critical life history stages involved in plant recruitment. We established 30 sample points, and each included an adult Mabea fistulifera tree, an Atta sexdens nest entrance, and six seed depots. We monitored the germination of M. fistulifera seeds for 3 months and subsequently followed the growth and mortality of the resulting seedlings for 12 months. Only the dispersal distance influenced plant establishment, reducing seed germination and increasing seedling growth, but with no effect of seed manipulation and deposition site. Despite the contrasting effects of distance on seed germination and seedling growth, the positive effect of dispersal distance on seedling growth was ten times greater than the negative effect on seed germination. Moreover, A. sexdens behaved neither as granivore nor as herbivore of M. fistulifera seeds or seedlings, which suggests that seed dispersal by A. sexdens is advantageous to M. fistulifera. Thus, the joint occurrence of these two species in disturbed areas could have a positive effect on this pioneer plant population, which might promote forest regeneration.

Keywords: Direct dispersal; Insect-plant interaction; Leaf-cutting ant; Seed-seedling conflict; Zoochory.