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Title:Primate nutritional ecology: the role of food selection, energy intake, and nutrient balancing in Mexican black howler monkey (Alouatta pigra) foraging strategies
Author(s):Righini, Nicoletta
Director of Research:Garber, Paul A.
Doctoral Committee Chair(s):Garber, Paul A.
Doctoral Committee Member(s):Stumpf, Rebecca M.; Ambrose, Stanley H.; Lambert, Joanna E.
Department / Program:Anthropology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Primate feeding ecology
Nutritional ecology
Geometric Framework
Alouatta pigra
Abstract:Studying primate nutritional ecology is critical for addressing questions related to individual and group-based decision making, feeding ecology, life history, and reproductive success. However, understanding food selection is a complex task, and it requires integrating information on physiology, behavior, and the ecological and social environments in which the animals live. In this dissertation, I examined the nutritional ecology of Mexican black howler monkeys (Alouatta pigra), an endangered nonhuman primate species characterized by a high intraspecific variability in time spent feeding on leaves, fruits, flowers, and other items (such as bark and stems) across seasons and study sites. Howler monkeys are considered the most folivorous New World primates, with leaves accounting for up to 100% of feeding time during certain months. Given assumptions regarding the challenges faced by foragers exploiting difficult to digest or high fiber foods that also may contain plant secondary compounds, howlers are considered energy-limited. While howler monkeys do consume a leaf-heavy diet during certain seasons of the year, and possess certain anatomical and physiological traits such as a capacious colon where fermentation occurs, a relatively long food transit time for their body mass, and molars with high shearing crests that contribute to the efficient processing of leafy material, describing them as folivores is an oversimplification of their dietary ecology. In this 15-month field study, I combined ecological, behavioral, and phytochemical data to analyze patterns of patch and food choice, nutrient and energy intake, and nutrient balancing in two groups (n = 14) of black howler monkeys inhabiting a 1400-ha semi-deciduous forest (“El Tormento”) in Campeche, Mexico. By following a single individual and recording its complete diet over the course of a single day, the amount in grams of each resource consumed, and the phytochemical characteristic of the food ingested, I constructed complete daily dietary profiles for each focal animal, and analyzed individual food choices using the Geometric Framework for nutrition. The GF is a multidimensional approach in which variables such as different food components and the amount of ingested nutrients are viewed in geometric space. The first chapter examines the role of resource mixing (i.e., switching between patches characterized by different types of resources and proportions of macronutrients) in individual feeding patch choice and patch leaving decisions. The second chapter analyzes the effects of plant phytochemical characteristics, including macronutrients and minerals, on individual food selection. The third chapter utilizes nutritional geometry to explore the synergistic effects of multiple nutrients and energy requirements on howler food choice across three different seasons (rainy, dry, and nortes). Finally, in the fourth chapter I outline the major conclusions and contributions of this research. I found that resource mixing offered the strongest explanation for feeding patch choices of black howler monkeys. This is based on data indicating that individuals frequently switched among complementary food items (e.g., from mature fruits to young leaves, from young leaves to immature fruits), moving from a lower protein patch to a higher protein food patch and vice versa. Moreover, neither patch depletion, satiation, nor social factors (e.g., intra-group aggression) were found to play an important role in individuals’ decisions to leave a patch. During the dry and rainy seasons, indices of howler food selectivity did not correlate with the nutrient and energetic content of foods consumed. This is not expected in a nutrient maximization model, but is consistent with the expectations of nutrient balancing. Based on the amount of food ingested (grams dry weight), howler monkeys were characterized by a fruit dominated diet (58% fruits, 37% leaves, 5% flowers), but this pattern differed among seasons. Leaves (mainly mature) were the most consumed food items during the nortes (49.5%). However, despite temporal changes in food consumption and food availability, and despite the fact that the food items consumed by howlers at El Tormento contained on average ~11% available protein, high levels of condensed tannins, and a low protein-to-fiber ratio (0.4 for young and mature leaves), across seasons the howlers consumed on average 102 kJ of available protein per metabolic body mass per day and 628 kJ/mbm of total energy. These values surpassed their daily requirements for protein and metabolizable energy, and were higher than those reported for primates considered ripe fruit specialists such as spider monkeys (Ateles spp.). Maintaining a balance in daily protein and non-protein energy intake was the most consistent strategy adopted by howler monkeys across all seasons of the year. These findings support the idea that howler monkey feeding strategies enable them to translate energy into rapid growth rates and high reproductive output compared to other atelines. Finally, this research supports the increasing recognition of nutrient balancing as a dietary strategy used by nonhuman primates to exploit nutritionally imbalanced and complementary foods in order to meet their dietary needs.
Issue Date:2014-05-30
Rights Information:Copyright 2014 Nicoletta Righini
Date Available in IDEALS:2014-05-30
Date Deposited:2014-05

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