Plants’ use of ants for dispersal at West Head, New South Wales

Abstract

Of the world’s known species of myrmecochores, plants which provide food bodies to induce ants to disperse their seeds, many are found in the dry sclerophyll vegetation of Australia. Here we present data and observations on myrmecochory on the West Head, and area of dry sclerophyll vegetation near Sydney, and in the light of these we discuss possible explanations for the distribution of myrmecochory. In most stands myrmecochores made up about 30% of the overall plant species complement, but few of the dominant species were myrmecochores. Myrmecochores tended to occur in a wider range of stands than non-myrmecochores. Within a stand, they tended to occur more of their own diameters from their nearest conspecific neighbours, but otherwise did not occupy detectably different microsites. Many proposed explanations for myrmecochory could explain either its commonness in Australia, or why it should be adaptive in sclerophyll shrubs, but none explain why it should be adaptive in sclerophyll shrubs in Australia but not in California or the Mediterranean. Australian dry sclerophyll vegetation, unlike that of California or the Mediterranean, is delimited by low-phosphorus soils; empirically, the correlation of myrmecochory with low-phosphorus soils is good. Evidence is given to suggest that in the vegetation of the West Head the limiting currency for seed production is phosphorus. Food bodies cost little phosphorus, so that myrmecochory is cheap in terms of the effective currency. However, wings and hairs are also cheap in terms of phosphorus.