Antagonistic and mutualistic interactions alter seed dispersal of understory plants at forest edges

Abstract

AbstractSeed dispersal by ants is an important interaction in North American eastern deciduous forests, where 30–40% of understory plants are myrmecochores, with seeds that possess lipid‐rich appendages (elaiosomes) that attract seed‐dispersing ants. Contemporary forests are fragmented and have regenerated from being previously cleared (secondary forests). In secondary forests, and especially along edges, myrmecochores are a depauperate component of forests. Here, we assess if seed dispersal of myrmecochores by ants, particularly the keystone disperser, Aphaenogaster sp., is intact in forest interiors compared to edges. In three North American northeastern deciduous forests, we compared myrmecochore cover and richness, seed dispersal by ants, and the abundance and richness of ants and other forest floor invertebrates between interiors and edges. We also conducted a seed removal experiment, excluding either ants, rodents (seed predators), or ants and rodents, to test their effects on seed dispersal between interiors and edges. We found differences in the composition of understory plants between interiors and edges, with edges lacking myrmecochores. We also found that seed dispersal by ants was lower in two of the three edges and corresponded to Aphaenogaster sp. abundance. Antagonistic interactions with an invasive slug that is an elaiosome robber, Arion subfuscus, was more apparent than damage by rodents in the experiment, negatively affected dispersal by ants more at edges than in interiors. Here we show that changes in mutualistic and antagonistic interactions affect seed dispersal at forest edges and that not all forest edges are the same, with some more intact than others. Understanding how seed dispersal is impacted in contemporary forests is important towards the goal of conserving and restoring depauperate forest understory communities.