Seed dispersal in South African trees: with a focus on the megafaunal fruit and their dispersal agents

Includes bibliographical referencesSeed dispersal is a key process. It is important in plant population biology because it influences the fate of seeds and the probability of recruitment, in plant biogeography since dispersal mode can influence the distribution range and rate of response to environmental change and habitat fragmentation, and in animal ecology since fruits can be an important dietary item (Wang and Smith, 2002). The majority of trees in the tropics (70 – 90%) and a large proportion of trees in temperate regions (up to 60%) rely on vertebrates for their dispersal (Howe and Smallwood, 1982; Fleming et al., 1987, Willson, 1990). Vertebrate dispersers range in size from 5g mistletoe birds (Dicaeidae) to 7,500,000g elephants (Elephantidae). The range and distribution of frugivore sizes is not uniform across ecosystems or geographical regions (Mack, 1993). These differences, one might suspect would be mirrored in the range and distribution of fruit size. This is not the case; in South America where the largest frugivorous mammal is the tapir (300kg; Hansen and Galetti, 2009), there is a subset of fruit that are conspicuously large. The paradoxical existence of such large fruit in the lowlands of Costa Rica was first noted by Janzen. In collaboration with Pleistocene faunal expert Paul Martin they conjectured that these fruit were ecological anachronisms that had evolved in the presence of large terrestrial vertebrates (>1000kg - megafauna) but had remained long after their demise (Janzen and Martin, 1982)