What effect temporally and spatially complex fruits may have on chimp cognition

Photo credit Sergio Morchon

A recent study by Janmaat and colleagues (2016) details how fruits in chimpanzee habitat are spatially and temporally complex (see that post here). As Janmaat and colleagues stated, this complexity in diet has implications for chimpanzee intelligence.

Fruits are a preferred food. It's worth hunting down these high-energy food items. That said, fruits aren't always easy to find. It's a waste of energy to travel to a specific fruiting tree with the thought of consuming a high-energy meal if that tree isn't producing. Wasting energy wandering around a forest looking for fruits that don't exist definitely isn't adaptive, and it's not something we would expect to see in chimpanzees or in any other species. It's in a chimpanzee's best interest to know where a fruit tree is and whether or not it will be fruiting. This type of processing  takes a certain amount of knowledge and brain power. 

The ecological intelligence hypothesis suggests that primates consuming foods that are fleeting in their availability and scattered geographically would require larger ranges and the cognitive capability to forage optimally for those ephemeral and scattered foods (Milton and May, 1976; Milton, 1980; Milton, 1981; Milton, 1988). Being able to remember where these scattered foods are and when they are available would be advantageous for the primate.

Janmaat and colleagues (2016) found substantial variation between fruiting species in regards to the timing of fruit production, and the authors suggest that chimps would benefit from learning species-specific fruiting patterns to locate these foods. There was also significant variation within a species in the monthly percentage of fruiting trees across years and between forests. Rather than this knowledge being genetic or something all chimpanzees are born with, it is more likely that chimpanzees learn about synchronicity of fruiting.

In regards to remembering trees that produce large amounts of fruit, the authors used existing literature and their own observations of great variation in fruit tree production histories to hypothesize that chimpanzees use their ranging patterns to monitor trees that are likely to produce large crops of fruit. Chimps would need to store information on fruit production histories over many years, particularly for species that fruit every few years rather than every few months, providing further evidence of how chimpanzees use their brains and intelligence to survive in their environment.

The forests chimpanzees inhabit clearly provide challenges for our closest relatives in terms of finding their preferred foods, ripe fruits. However, these intelligent animals have the brain power needed to master this environment and the challenges forests present. Their intelligence not only helps them navigate living in a social group and managing complex relationships but it also allows them to navigate the complex ecology surrounding them.

Links of possible interest:
Chimpanzees and long term memory
NOVA's Ape Genius


Works cited:

Milton, K., & May, M. L. (1976). Body weight, diet and home range area in primates. Nature, 259(5543), 459-462.

Milton, K. (1980). The foraging strategy of howler monkeys: a study in primate economics. Columbia University Press.

Milton, K. (1981). Distribution patterns of tropical plant foods as an evolutionary stimulus to primate mental development. American Anthropologist, 83(3), 534-548.

Milton K. 1988. Foraging behaviour and the evolution of primate intelligence. In: Byrne RW, Whiten A, editors. Machiavellian intelligence: social expertise and the evolution of intellect in monkeys, apes and humans. Oxford: Clarendon Press. p 285–305.

Gorillas and humans diverged from one another earlier than thought

Studying ancient humans and primates tells us more about our owns selves and what it means to be human, what it means to be of the species modern Homo sapiens. While we can look at our closest living relatives, apes and other primates, to theorize a great deal about how our ancestors acted  5 million years ago (mya), we also rely on fossil evidence and genetic studies. Studying human ancestors presents one very large problem: lack of fossil evidence. The fossilization process requires just the right conditions at time of death and the right conditions afterwards.  Thus, there are many gaps in our knowledge because the data simply isn't available. The fossils haven't been found.

Juvenile mountain gorillas, Photo credit: Philip Milne

Scientists are particularly interested in fossils from 12-7 mya because this is around the time when African apes (gorillas, chimpanzees, and bonobos) and humans split. Yet, few fossils from this time have been discovered.

Katoh and colleagues (2016) studied fossilized teeth found in Ethiopia's Afar Rift from an ancestral gorilla, called Choroapithecus abyssinicus, and the surrounding layers of earth these fossils were found in. Their results that suggest C. abyssinicus is older than previously believed. The teeth have been dated to 8 mya, which would mean that these ancestral gorillas and ancestral humans had to have diverged earlier in time than previously thought.

Previous estimates of the split between African apes and humans suggested the two lines diverged more recently. Data from genetics suggests that humans and gorillas split somewhere between seven to eight million years ago.  When C. abyssinicus was first discovered, it was found in deposits that are older than 8mya. The geology previously suggested that this species lived 10-10.5 mya (Suwa et al., 2007). Thus, this study provides some needed clarity on the age of these fossils.

With these new results, we can place the age of these fossils at 8 mya, meaning this ancestral ape and humans likely split around 10 mya rather than 8 mya and suggesting the mutation rate between the two was slower than previously thought. We can also confirm that ancestral great apes evolved in Africa, as opposed to Europe or Asia.

It's always impressive how a few extra teeth and a lot of hard work can transform what we know about our own origins.

Works cited:

Katoh, S., Beyene, Y., Itaya, T., Hyodo, H., Hyodo, M., Yagi, K., ... & Nakaya, H. (2016). New geological and palaeontological age constraint for the gorilla–human lineage split. Nature, 530(7589), 215-218.

Suwa, G., Kono, R. T., Katoh, S., Asfaw, B., & Beyene, Y. (2007). A new species of great ape from the late Miocene epoch in Ethiopia. Nature, 448(7156), 921-924.

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.