NUTRIENT COSTS OF VERTEBRATE-DISPERSED AND ANT-DISPERSED FRUITS

1. In Australia, plant species with fleshy fruits adapted for dispersal by vertebrates are concentrated on fertile soils and species adapted for dispersal by ants on infertile soils. 2. We tested some predictions of a hypothesis that availability of a specific mineral nutrient or nutrients may limit the production of fleshy fruit and so tend to confine frugivory to relatively fertile soils. 3. Nutrient concentrations were compared in the dispersal structures of 22 elaiosome-bearing, 29 fleshy-fruited and five arillate plant species. Discriminant function analysis revealed that K and N were the only nutrients that significantly separated the different dispersal structures. Potassium concentration in the fleshy pulp of vertebrate-dispersed diaspores was significantly higher than in elaisomes of ant-dispersed diaspores. Nitrogen content of elaiosomes was significantly higher than of flesh. Nitrogen and K content of arils was similar to that of elaiosomes but was significantly different from fleshy pulp. Plant species with different dispersal modes, growing at the same site, showed the same differences in K and N concentrations. 4. The hypothesis that fleshy fruit production is limited by the availability of a specific nutrient or nutrients was therefore rejected for all nutrients except K. An examination of dispersal spectra in relation to K availability, rather than to general soil fertility may help explain the observed correlation between dispersal mode and soil fertility in Australia and South Africa.