Tuesday, February 2, 2016

The spatial and temporal complexity of fruit species consumed by chimps

Chimpanzees live in a variety of environments, thus the types of food they consume vary accordingly. We wouldn't expect a chimpanzee troop living in Fongoli (a savanna) to consume the same foods as chimpanzees living in Gombe (a tropical forest).

That caveat aside, chimpanzees across habitats prefer fruits to other food types. We know this because fruits make up a greater proportion of their diet than would be expected given fruit availability (Hladik, 1977; Tutin et al., 1997; Conklin-Brittain et al., 1998; Wrangham et al., 1998; Doran-Sheehy et al., 2006). Fruits are high in energy and low in secondary compounds, or digestive inhibitors or toxins, such as tannins or lignin. (Remember that the fruits we see in a grocery store or at a food stand have been selectively bred to look and taste considerably different than most wild fruits). Interestingly, chimpanzees in Guinea-Bissau consume mainly wild fruits and flowers even when they are in close proximity to agricultural areas (Carvalho et al., 2015). Thus, it seems safe to conclude that fruits are high up on the desired menu.

Feeding on Ficus sur fruits, Photo credit: Alain Houle
A recent study by Janmaat and colleagues (2016) looked at three populations of chimpanzees in tropical lowland rainforest, lowland tropical moist forest, and a moist evergreen tropical forest to better understand how chimpanzees access energy-rich foods. They considered multiple food types that are high-energy: young leaves, unripe fruit, and ripe fruit. The authors also had a particular interest in large crops of ripe fruit. They described the probability of finding trees for each of the aforementioned, three food types and how predictable ripe fruit production is in each focal tree in regards to timing, frequency, and quantity of ripe fruit produced. 

 The authors found that individuals were more likely to encounter young leaves or unripe fruit than ripe fruit, confirming that fruits present more of a challenge than other food types. However, over half of all of the trees chimpanzees encountered over the course of this study were species of fruiting trees consumed by chimps. Thus, finding a tree species known to produce an edible fruit isn't a monumental challenge for these populations. The challenge lies in timing.  

There was considerable variation in the timing of fruit production within a population of a tree species. Within the same species, the length of fruit production varied: one individual may produce fruit for a few months over multiple years whereas another individual may fruit for many more months within the same period. There was also monthly variation in the size of fruit crops produced. Further variation within a species complicates matters for chimps even more, as they can't count on large crops of fruits in certain months, even within individual species.

Look for an upcoming post on the implications of finding ripe fruits in a complex environment. How might the ecology of chimpanzee habitat and their dietary choices affect their intelligence?

Links of potential interest:
Chimps understand and choose to cook
Female chimpanzees more likely to use tools when hunting than males

Works cited:

Carvalho, J. S., Vicente, L., & Marques, T. A. (2015). Chimpanzee (Pan troglodytes verus) Diet Composition and Food Availability in a Human-Modified Landscape at Lagoas de Cufada Natural Park, Guinea-Bissau. International Journal of Primatology, 36(4), 802-822. 
Conklin-Brittain, N. L., Wrangham, R. W., & Hunt, K. D. (1998). Dietary response of chimpanzees and cercopithecines to seasonal variation in fruit abundance. II. Macronutrients. International Journal of Primatology, 19(6), 971-998.
Doran-Sheehy, D. M., Shah, N. F., & Heimbauer, L. A. (2006). Sympatric western gorilla and mangabey diet: re-examination of ape and monkey foraging strategies. Cambridge Studies in Biological and Evolutionary Anthropology, 48, 49.
Hladik, C. M. (1977). Chimpanzees of Gabon and chimpanzees of Gombe: some comparative data on the diet. Primate Ecology: Studies of Feeding and Ranging behaviour in Lemurs, Monkeys, and Apes, 81-501.
Janmaat, K. R., Boesch, C., Byrne, R., Chapman, C. A., Bi, G., Zoro, B., ... & Polansky, L. (2016). Spatio‐temporal complexity of chimpanzee food: How cognitive adaptations can counteract the ephemeral nature of ripe fruit. American Journal of Primatology.
Tutin, C. E., Ham, R. M., White, L. J., & Harrison, M. J. (1997). The primate community of the Lopé Reserve, Gabon: diets, responses to fruit scarcity, and effects on biomass. American Journal of Primatology, 42(1), 1-24.
Wrangham, R. W., Conklin-Brittain, N. L., & Hunt, K. D. (1998). Dietary response of chimpanzees and cercopithecines to seasonal variation in fruit abundance. I. Antifeedants. International Journal of Primatology, 19(6), 949-970.

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