Interactions between ants and seeds of two myrmecochorous plant species in recently burnt and long‐unburnt forest sites

TLDR: Differences in the proportions of seeds removed, elaiosomes robbed and seeds ignored appeared to be largely driven by an increase in abundance of A. nr. nitidiceps and a decrease in abundances of M. sydneyense in burnt vegetation.

Abstract: Myrmecochory (seed dispersal by ants) is a common seed dispersal strategy of plants in fire-prone sclerophyll vegetation of Australia, yet there is little understanding of how fire history may influence this seed dispersal mutualism. We investigated the initial fate of seeds of two myrmecochorous plant species, the small-seeded Pultenaea daphnoides J.C. Wendl. and the large-seeded Acacia pycnantha Benth., in replicated burnt (3.25 years since fire) and unburnt (53 years since fire) forest plots in the Mount Lofty Ranges, South Australia. Specifically we measured (i) seed removal rates; (ii) the frequency of three ant–seed interactions (seed removal, elaiosome robbery and seed ignoring); (iii) the relative contribution of different ant species to ant–seed interactions; and (iv) the abundance of common interacting ant species. Rates of seed removal from depots and the proportion of seeds removed were higher in recently burnt vegetation and the magnitude of these effects was greater for the smaller-seeded P. daphnoides. The overall proportion of elaiosomes robbed was higher in unburnt vegetation; however, the decrease in elaiosome robbery in burnt vegetation was greater for P. daphnoides than for A. pycnantha. Ants ignored seeds more frequently in burnt vegetation and at similar rates for both seed species. In total, 20 ant species were observed interacting with seeds; however, three common ant species accounted for 66.3% of ant–seed interactions. Monomorium sydneyense almost exclusively robbed elaiosomes, Rhytidoponera metallica typically removed seeds and Anonychomyrma nr. nitidiceps showed a mix of the three behaviours towards seeds. Differences in the proportions of seeds removed, elaiosomes robbed and seeds ignored appeared to be largely driven by an increase in abundance of A. nr. nitidiceps and a decrease in abundance of M. sydneyense in burnt vegetation. Understanding how these fire-driven changes in the initial fate of myrmecochorous seeds affect plant fitness requires further investigation.