|Photo credit Sergio Morchon|
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
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.