This New York Times article, written by Anthony Di Fiore, a primate biologist at NYU, talks about the day he encountered an interaction between Woolly and Spider monkeys
(First picture below on the left: Woolly Monkey. On the left: Spider Monkey)
Although the time of the interaction was small (~15mins), Professor De Fiore may be getting to something big. Most species don’t interact outside of their own, even if they share a common ancestor. Even within own species, it is rare that they interact outside of the herd (For example, chimpanzees live with their herd but if chimpanzees outside of the herd they are not welcomed) . So how could two different species interact, even co-exist in the same place,without any conflict?
One possible theory I have come up is that the interaction was possible because it happened during meal time. In human, intake of food makes people happy. Food may have similar effect on these monkeys as well, and since the interaction happened right after food intake, they were happy enough to tolerate presence of other specie. This would also explain the short interaction time – the feeling of “happiness” disappeared and they quickly became aware of possible threats to each other.
Another possibility is that they have some benefit by being together for a short period of time. Many individual means more eyes for predators. This is crucially important during meal time. Therefore, each specie are benefiting by each other’s presence.
Neither of them may not be the case, but this may be an interesting case to be doing an observation for.