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Identifying the degree to which primates alter their behavior and diets to different ecological conditions has significant implications for examining functional morphology, modeling socioecology and feeding competition, and developing primate conservation strategies. This study seeks to determine if Angola black and white colobus monkeys (Colobus angolensis palliatus) employ consistent dietary section criteria by investigating the behavior and diet of three groups inhabiting ecologically distinct areas of Kenya’s Diani Forest. The primary goals of this research are to examine feeding ecology, dietary flexibility, and food selection in relation to 1) seasonal and spatial availability, 2) mechanical toughness, and 3) nutritional composition of food items. Behavioral data were collected on three habituated groups (Ujamaa, Ufalme, and Nyumbani) over 267 days from July 2014 – December 2015. Behavioral data were recorded using a combination of instantaneous scan sampling and focal follows. Food availability was estimated by combining tree species composition profiles of home ranges with phenology data. Mechanical toughness was recorded with a portable test instrument. Nutritional composition of food items was calculated using a combination of traditional wet chemistry assays and near-infrared reflectance spectroscopy (NIRS) predictive models. Home ranges of the three groups differed significantly with regard to tree species composition and food availability. Diets differed considerably with regard to plant species and species-specific plant parts: only three species ranked in the top 20 food species for all three groups and mean monthly dietary overlap was just 10.4% among all groups. Dietary idiosyncrasies were not readily explained by differences in spatial and temporal availability of the most abundant tree species within the groups’ home ranges (i.e., all groups selected rare tree species and plant parts from their ranges). Leaf toughness was not a strong predictor of food selection; however, toughness significantly impacted foraging efficiency. Leaf toughness negatively correlated with ingestion rate (i.e., g/min) and positively correlated with masticatory investment (i.e., chews/g). NIRS models of nutritional components had strong predictive power despite the highly heterogeneous sample set. Conventional fiber limitation and protein to fiber ratio maximization models explained leaf selection in two of the three groups and one of the three groups, respectively. Despite significant differences in consumption of species-specific plant parts and quantity of kilocalories consumed per day, individuals of different groups balanced their intake of non-protein energy (NPE) and available protein energy (AP) to a consistent ratio of approximately 2:1.This study emphasizes that aspects of behavior and diet can vary considerably among groups living in different areas within the same forest. While availability, mechanical toughness, and nutritional composition of plant parts influenced food selection to varying degrees, maintaining a consistent NPE to AP intake (i.e., intake target) was the only consistent pattern among all three groups. Intake targets can be achieved by consistently consuming foods whose nutritional composition is close to or equal to that of the target or by consuming foods with disparate, yet complementary nutritional compositions. Unlike traditional models of food selection (e.g. protein maximization), the Geometric Framework provides a theoretical approach that can be universally applied to all investigations of primate feeding ecology. |
