Can Disruption of an Ant–Plant Mutualism Explain a Lack of Recovery of Forest Herbs in Post-Agricultural Forests of New York?

Abstract

A substantial proportion New York's forests regenerated following agricultural abandonment around the turn of the 20th century. Many myrmecochorous (ant-dispersed) plant species are lacking in these forests decades after land abandonment despite being present in residual stands. To determine if disruption to this ant–plant mutualism can partially explain the current distribution patterns of myrmecochorous plants, we quantified the proportion of seeds removed by ants while accounting for predation by rodents in residual and post-agricultural forests. We experimentally manipulated ant access and controlled for rodent access to seeds of 3 myrmecochorous understory herbs in 3 paired residual and post-agricultural forests in central New York. We identified Aphaenogaster rudis as the primary seed disperser. We found no difference in mean (± 1 SE) proportion of seeds removed by ants between residual stands (73.7% ± 7.7%) and post-agricultural stands (75.8% ± 7.9%). Rodents removed few to no seeds (5.3% ± 1.5%), but an invasive slug, Arion subfuscus (Dusky Arion), was observed removing elaiosomes from seeds in both stand types. Our data indicated neither a lack of ant-dispersal activity nor excessive rodent predation would be limiting to dispersal of myrmecochorous seeds in post-agricultural forests during the period of our study. Given the presence of A. rudis in post-agricultural stands, programs to assist plant migration will likely be sufficient to reestablish this ant–plant mutualism in degraded sites.