SHELL STRENGTH AND PRIMATE SEED PREDATION OF NONTOXIC SPECIES IN EASTERN AND SOUTHERN AFRICA

The large African primates that eat fruit destroy the seeds of a number of fruiting species. This paper addresses several questions about seed-eating. What is the nature of the dietary niche provided by the nonpoisonous seeds of eastern and southern Africa? How well are these seeds mechanically protected? What other means of reducing seed predation are employed by the plants? and is the niche ecologically stable? Measurements of seed shell strength on 3 7 species from 17 families reveal a range of values, from <100-kg (numerous species) to over 2000-kg (palm nuts) breaking load. Primates crack open with their teeth seed shells from species exhibiting test strengths less than 600 kg. Variation in shell strength appears to increase dramatically for average species strengths above 100 kg. Plant species are not characterized by specific shell strengths but instead, display envelopes of shell strength overlapping broadly with other species. Taking this into account, adult male baboons (Papio spp.) appear to be dentally capable of preying upon most of the seed species of eastern and southern Africa. The possibility for predation of nonpoisonous seeds exists primarily because the plants periodically produce large crops in synchrony and the hard-shelled seeds are effectively dispersed, sometimes explosively but more often by means of edible fruits. The concomitant primate seed predation is a facultative specialization, of little apparent threat to the community of plants that support it.