Vulnerable broom crowberry (Corema conradii) benefits from ant seed dispersal in coastal US heathlands

Ant seed dispersal is a globally important mutualism that occurs in over 10,000 plant species. Relatively little research has been conducted on ant seed dispersal of Corema conradii (broom crowberry), a key constituent of globally threatened coastal heathland ecosystems where fire is part of the disturbance regime. We conducted field studies at Cape Cod National Seashore, MA, USA to better understand the fruiting biology of C. conradii and to explore the benefits of ant seed dispersal. We identified how C. conradii fruit is displayed to foraging ants, determined the ant species that disperse C. conradii fruit, and quantified the distance that ants disperse fruit. We hypothesized that ants would disperse fruit away from C. conradii parent plants that become burn footprints following fire, to ensure seed dispersal to suitable germination sites, where we expected to find higher seedling establishment. We recorded eight ant species dispersing the fruit of C. conradii an average distance of 136 cm (±10.45) (range: 7–641 cm). Two ant species, Aphaenogaster treatae and Formica dolosa, dispersed 60 % of fruit in fruit-baiting experiments, suggesting they may function as primary dispersers in this system. Ants dispersed fruit outside the burn footprints 82 % of the time, and seedlings occurred outside the burn footprints 90 % of the time. Our results suggest that ant seed dispersal confers important reproductive benefits to C. conradii by directing seed dispersal sufficient distances away from parent plants onto suitable substrates for germination after intense, episodic fires.