Intratree Variation in Fruit Production and Implications for Primate Foraging
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- Houle, A., Chapman, C.A. & Vickery, W.L. Int J Primatol (2007) 28: 1197. doi:10.1007/s10764-007-9214-9
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We tested the hypothesis that fruit quantity and quality vary vertically within trees. We quantified intratree fruit production before exploitation by frugivores at different heights in 89 trees from 17 species fed on by primates in Kibale National Park, Uganda. We also conducted a pilot study to determine if the nutritional value of fruit varied within tree crowns. Depending on the species and crown size, we divided tree canopies into 2 or 3 vertical layers. In 2-layered trees, upper crowns produced fruits that were 9.6–30.1% bigger and 0.52–140 times the densities of those from lower crowns, with one exception. Among 2-layered trees, upper crowns produced a mean of 46.9 fruits/m3 (median 12.1), while lower crowns produced a mean of 14.1 fruits/m3 (median 2.5). Among 3-layered trees, upper crowns produced a mean density of 49.9 fruits/m3 (median 12.5), middle crowns a mean of 16.8 fruits/m3 (median 6.6), and lower crowns a mean of 12.8 fruits/m3 (median 1.8). Dry pulp and moisture were systematically greater per fruit in the highest compared to the lowest canopy layers (22.4% and 16.4% respectively in 2-layered trees, 49.7% and 21.8% respectively in 3-layered trees). In 1 tree of Diospyros abyssinica, a pilot nutritional study showed that upper crown ripe fruit contained 41.9% more sugar, 8.4% more crude proteins, and 1.8 times less of the potentially toxic saponin than lower crown ripe fruit, but the result needs to be verified with more individuals and species of trees. We discuss the consequences of intratree variations in fruit production with respect to competition among frugivorous primates.