Myrmecochorous plants and their ant seed dispersers through successional stages in temperate cove forests

Abstract

Anthropogenic disturbance can decrease woodland diversity in the species-rich herbaceous layer of eastern deciduous forests, and ant-dispersed (myrmecochorous) plants may be particularly affected due to their limited ability to re-colonise secondary forests. Consequently, we predicted that myrmecochorous plants and their keystone seed-dispersing ants would increase with time since the last disturbance, as reflected by young, middle or mature forest successional stage. Specifically, we hypothesized that myrmecochore abundance and richness would be relatively lowest in the youngest forests, moderate in middle-aged forests and highest in mature forests. We also hypothesized that experimentally introducing ant bait in a regular pattern, as might be expected from intact species-rich myrmecochore communities, would elicit greater ant foraging interest than intermittent baiting, as might be expected in recently disturbed depauperate myrmecochore communities. We found the highest myrmecochore plant abundance in mature forests, but we found the same for herbaceous plants overall. Moreover, regular and intermittent bait offerings elicited similar overall ant responses. The observational results suggested that myrmecochorous plants respond to forest successional stage as do other woodland plants, and our experimental results suggest that disrupted seed delivery by myrmecochores did not affect Aphaenogaster abundance or foraging behaviour. As such, the myrmecochore communities studied here appeared as resilient as other woodland herbs, and seed-dispersing ants did not appear dependent on myrmecochore plant communities. Indeed, given the relatively high myrmecochore richness and abundance across our study sites, forest type (e.g., rich cove forest) might better predict myrmecochore success than successional stage.