Seed 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.

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Mutualistic interactions provide essential ecosystem functions, such as promoting and maintaining diversity. Understanding if functionally important mutualisms are resilient (able to resist and recover) to anthropogenic disturbance is important to understand the capacity for diversity to recover. Animal-mediated seed dispersal supports plant population growth and community structure, and disturbance of this function can threaten plant diversity and contribute to low resiliency. Ant-mediated seed dispersal mutualisms are particularly sensitive to anthropogenic disturbance, as they rely on one to a few high-quality dispersal partners. In North American eastern deciduous forests (NAEDF), ants in the genus Aphaenogaster are keystone dispersers of 30-40% of understory forbs adapted to dispersal by ants (myrmecochores). The majority of present day NAEDF have regenerated from previous disturbance in the form of historical land use change (HLUC), due to clearing for agriculture. Previous studies have revealed that myrmecochore diversity is not resilient to HLUC. Here, we ask if seed dispersal mutualisms are resilient to HLUC and if decreases in mutualistic interactions with partners, Aphaenogaster sp., or increases in antagonistic interactions cause degradation of function. In a large-scale natural experiment (20 sites), we measured seed removal, the abundance of mutualistic partners and other invertebrates interacting with seeds, myrmecochore cover and diversity, along with ant habitat and forest structure. We found lower and more variable seed removal in secondary forests compared to remnant forests. A path analysis of all forests revealed that abundance of mutualists was the primary determinant of variation in seed removal, and that seed damage by antagonists (invasive slugs) negatively affected dispersal and was higher in secondary forests. In a path analysis of remnant forests, the link between mutualist abundance and seed removal was absent, but present in the secondary forest path, suggesting that seed dispersal is more variable and dependent on mutualist abundance in secondary forests and is stable and high in remnant forests. Here we show that functional resilience to HLUC is variable and may impede recovery of understory plant communities. This work provides key insights on the effects of anthropogenic disturbance on mutualistic interactions and how the resilience of critical ecosystem functions impacts diversity resiliency.

Mutualistic interactions provide essential ecosystem functions that contribute to promoting and maintaining diversity in ecosystems. Understanding if functionally important mutualisms are "resilient" (i.e., able to resist or recover) to anthropogenic disturbance is essential for revealing the capacity for diversity to recover. Animal-mediated seed dispersal supports plant population growth and influences community structure, and disturbance affecting seed dispersal can contribute to low resiliency of plant diversity. Ant-seed dispersal mutualisms are sensitive to anthropogenic disturbance, as they rely on one to a few high-quality dispersal partners. In North American eastern deciduous forests, ants in the genus Aphaenogaster are "keystone dispersers" of understory forbs adapted to dispersal by ants (myrmecochores), which make up more than one-third of the understory herbaceous community. The majority of forests within this region have regenerated from previous disturbance in the form of clearing for agriculture. Previous studies have revealed that myrmecochore diversity is not resilient to previous clearing. Here, we ask if seed dispersal mutualisms are resilient to historical forest disturbance and if decreases in mutualistic interactions with partners, Aphaenogaster sp., or increases in antagonistic interactions cause degradation of function. In a large-scale natural experiment (20 sites), we measured seed removal, the abundance of mutualis-