To explore sources of variation in tropical forest primate biomass, and, in particular, to test the hypothesis that soil conditions are a major ultimate determinant of the biomass of colobine monkeys and other primates, we compared data on the soils, vegetation, and primate community at a site in West Africa (Tiwai Island, Sierra Leone) with information from other sites, especially two other African sites (Douala—Edea in Cameroon, and Kibale Forest in Uganda). The biomass of eight anthropoid primate species in old secondary high forest on Tiwai was estimated from data on population densities assessed by transect samples combined with data on social group densities and individual body masses. Samples of soil and tree foliage were collected at the same site, and subjected to a variety of chemical and mechanical analyses. Our estimate of anthropoid biomass at Tiwai is 1229—1529 kg/km2, including 682—889 kg/km2 of colobines. This is one of the highest primate biomasses recorded anywhere. The soils at Tiwai were found to be relatively high in sand content and low in pH, and to have low levels of mineral nutrients. Levels of condensed tannins in the mature foliage of the trees comprising a major part of the forest canopy were higher than at other sites, but the ratio of protein to fiber in this foliage was also higher than at any other site except Kibale. It is argued that a wide range of environmental factors affect primate population densities, and that nutrient—poor soils and high tannin levels in tree foliage do not necessarily produce a low primate (or colobine) biomass, as some earlier studies had suggested. Furthermore, seeds (an important food source for Tiwai colobines) are apparently a common part of the colobine dietary repertoire and are not consumed largely as a response to a scarcity of digestible foliage.

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SummaryColobine monkeys are widely reported to spend considerable portions of their daily activity budgets resting. To test the hypothesis that resting and associated postures are related to energy conservation and thermoregulation, resting behaviours in Colobus polykomos are examined in relation to vegetation cover, weather conditions and diet. Seasonal differences in hunching are shown to be significantly correlated with cool, wet conditions and low energy intake, while postures associated with heat dissipation are more closely related to hot weather. These results support the hypothesis that C. polykomos are energy limited in wet seasons, and suggest their behaviourial thermoregulation is related not just to climatic conditions, but also to energy content and availability of food.RésuméOn a rapporté largement que les colobidés passent une grande partie de leur temps à se reposer. Pour éprouver l'hypothèse selon laquelle le repos et les attitudes qui s'y associent seraient liés à la conservation de l'énergie et à la thermorégulation, on examine les comportements de repos chez Colobus polykomos en relation avec le couvert végétal, les conditions atmosphériques et le régime alimentaire. On montre que les différences saisonnières de la chasse sont significativement liées à des conditions fraîches et humides et à une faible absorption d'énergie alors que les attitudes qui dépensent de la chaleur sont plus étroitement liées au temps chaud. Ces résultats supportent l'hypothèse que C. polykomos dispose d'une énergie limitée en saison des pluies et suggèrent que la thermorégulation active n'est pas liée uniquement aux conditions climatiques mais aussi au contenu énergétique et à la disponibilité de la nourriture.