Feeding in Forest Chimpanzees: Do Food Type and Canopy Location Predict Positional Behavior?

Area of Science:

• Primate Ecology
• Paleoanthropology
• Behavioral Ecology

Background:

• Great ape anatomy and positional behaviors, such as upright torso stability and suspension, are often linked to ripe fruit consumption in canopy terminal zones.
• However, fossil evidence prompts re-evaluation of these hypotheses.

Purpose of the Study:

• This study investigates the relationships between feeding posture, food type, and canopy zone in chimpanzees.
• It aims to test the hypothesis that specific feeding behaviors evolved to support specialized diets in arboreal environments.

Main Methods:

• Focal follow data were collected over 10 months on 103 chimpanzees in Kibale Forest, Uganda.
• Generalized Linear Mixed Modeling analyzed the effects of food type, canopy location, and age on arboreal feeding posture versatility.
• Branch and tree characteristics were also examined.

Main Results:

• Consuming leaves versus ripe fruit increased feeding posture versatility across all trees.
• In large-canopy trees, unripe versus ripe fruit consumption negatively affected versatility.
• Terminal zone feeding increased versatility, with leaf consumption in this zone negatively impacting it.

Conclusions:

• A positive "terminal zone effect" on versatility was observed in large trees, influenced by food type.
• Leaf consumption over ripe fruit enhanced versatility in the overall forest context.
• These results indicate that varied combinations of food type and availability can lead to similar outcomes (equifinality) in great ape positional versatility, suggesting that hominoid specializations can arise in multiple ecological settings.