Table 1.
Social group, age, sex and rank of chimpanzees in this study.
Figure 1.
The tower was constructed of steel mesh and rods that allowed the chimpanzees to see clearly inside the tower. Food was only accessible from the top of the tower if the hanging tray was raised to the top without tipping the tray such that all the food fell to the bottom of the tower. Along the bottom edges of the tower were steel panels to discourage chimpanzees from attempting (in vain) to access fallen food from the ground. The tower was baited through a pipe that extended from the side of the tower to the outside of the room. The size of the chimpanzee is to scale relative to the tower (drawn from photo of adult chimpanzee BOB).
Figure 2.
Change in Rewards Obtained from Solo Sessions when in the Presence of Higher and Lower Ranked Individuals.
The number of rewards obtained with higher and lower ranking partners was subtracted from the number of rewards obtained in solo sessions. Subjects from Group 3 and 4 are represented by open and closed circles, respectively. Statistics were calculated only on subjects tested with both higher and lower ranking partners in Group 4 (Wilcoxon signed ranks test, W = 21, N = 6, P = 0.031).
Figure 3.
Dyadic Association Index & Time Shared on Tower.
The y-axis shows the duration in seconds in which both chimpanzees were located on top of the tower during dyadic sessions. The x-axis shows the twice-weight association index generated from six months of focal follows. Dyads that showed at least one occurrence of cooperative problem solving are represented by a square (with the exception of the dyad LOU & BUF because no AI was available). In both social groups, there was a significant positive correlation between AI and time shared on the tower (Mantel tests, Group 3: rS = 1, N = 6, P<0.01; Group 4: rS = 1, N = 8, P<0.01).
Table 2.
Frequency of sessions with and without aggression, categorized by whether collaborative problem solving occurred in the session.
Table 3.
Frequency of sessions with and without aggression, categorized by whether one chimpanzee, two chimpanzees, or neither chimpanzee solved the task in the session.