Secondary removal of seeds dispersed by chimpanzees in a Nigerian montane forest

What volume of seeds can a chimpanzee carry in its body?

Great apes are important seed dispersers with large bodies, able to swallow large seeds and travel long distances. Although there have been several studies investigating seed dispersal quality [sensu Schupp (Vegetatio 107/108:15-29, 1993)] by chimpanzees, there is little information on the volume of seeds they can carry in their bodies. When a relatively fresh corpse of a mature female chimpanzee was found at Mahale, Tanzania, we took advantage of the rare opportunity to investigate the total weight and cubic volume of seeds recovered from the corpse. The seeds contained in the corpse weighed 258.8 g (dry weight) and measured 489.4 cm³. The volume of seeds was 14.7 % of the previously reported capacity of the digestive tract of a chimpanzee in captivity. We also indirectly estimated the volume of seeds from the values of observed seed volume in feces, the reported number of defecations per day, and the seed passage time. The estimated volume was significantly lower than the observed seed volume, suggesting that the number of defecations per day is underestimated because it may not include nighttime defecation.

Seed-dispersal ecology of tropical montane forests

Seed-dispersal ecology in tropical montane forests (TMF) differs in some predictable ways from tropical lowland forests (TLF). Environmental, biogeographic and biotic factors together shape dispersal syndromes which in turn influence forest structure and community composition. Data on diaspore traits along five elevational gradients from forests in Thailand, the Philippines, Tanzania, Malawi and Nigeria showed that diaspore size decreases with increasing altitude, fleshy fruits remain the most common fruit type but the relative proportion of wind-dispersed diaspores increases with altitude. Probably corresponding to diaspore size decreasing with increasing elevation, we also provide evidence that avian body size and gape width decrease with increasing altitude. Among other notable changes in the frugivorous fauna across elevational gradients, we found quantitative evidence illustrating that the proportion of bird versus mammalian frugivores increases with altitude, while TMF primates decrease in diversity and density, and switch diets to include less fruit and more leaf proportionately. A paucity of studies on dispersal distance and seed shadows, the dispersal/predation balance and density-dependent mortality thwart much-needed conclusive comparisons of seed dispersal ecology between TMF and TLF, especially from understudied Asian forests. We examine the available evidence, reveal knowledge gaps and recommend research to enhance our understanding of seed dispersal ecology in tropical forests. This review demonstrates that seed dispersal is a more deterministic and important process in tropical montane forests than has been previously appreciated.