Fazendo a feira: primatas uacaris (Cacajao, Pitheciidae) selecionam frutos de tamanho ideal para uma refeição parcimoniosa.

Abstract

Optimal foraging theory predicts that animals will seek simultaneously to minimize food processing time and maximize energetic gain. To test this hypothesis, we evaluated whether a specialist seed-predator primate forages optimally when choosing among variable-sized thick-husked fruits. Our objects of study were the golden-backed-uacari (Cacajao ouakary, Pitheciidae) and single seeded pods of the macucu tree (Aldina latifolia, Fabaceae). We predict that golden-backed-uacari will consume fruits of the size class that requires the least time to obtain, handle, and ingest. We used scan-sampling, ad libitum to record feeding observations, and measured fruits, their penetrability and the size of taxidermised C. ouakary hands. To test if uacaris selected for optimal characteristics, we compared 8 metrics from 75 eaten and 105 uneaten seeds/fruits collected. Uacaris selected fruits of medium size and weight disproportionately to their abundance. Processing large fruits took six times longer than did medium-sized fruits, but seeds were only four times as large, that is, for energetic yield per unit time, thus choosing medium-sized pods was optimal. Disproportionate selection by C. ouakary of fruits of medium size and mass in relation to their abundance suggests active sub-sampling of the available weight-size continuum. This selectivity probably maximizes trade-offs between the energy derived from a seed, and time and energy expended in processing fruit to access this, so following optimal foraging theory predictions. The greater time spent processing large pods is attributed to difficulties manipulating objects five to seven times the size of the animal’s palm and one-sixth its own body weight. Vertebrate food items rarely occur in uniform sizes. Animals are, therefore, often limited by food item sizes exceeding gape size, or which are either difficult or time-consuming to handle. Frugivorous primate anatomy may therefore limit consumption of fruits large in relation to the size of the hands and mouth, as processing them can result in larger energetic demands via the increased effort required when handling, opening and chewing such fruit. Given the above, the objective of this study was to analyse the grip and the maximum capacity of the mouth to accommodate fruit, and determine whether such parameters form selection criteria in determining fruits types eaten by of members of the genus Cacajao. To test this, four uacari (Pitheciidae) taxa were used (Cacajao c. calvus [Geoffroy Saint-Hilaire, 1847], C. c. ucayalii [Thomas, 1928], C. melanocephalus [Humboldt, 1812] and C. ouakary [Spix, 1823]), and study area species, including eaten and non-eaten fruit species, and compared these with hand and gape sizes from specimens in zoological collections, divided into three categories (easy, manageable and difficult handling/ingesting), and tested using a contingency table with Chi-square statistics. Except for C. melanocephalus, uacaris, when choosing diet species, appear not to use size of fruit-based levels of difficulty as selection criteria. Diets of C. c. calvus, C. c. ucayalii and C. ouakary large proportions of easy-to-handle fruit species in their diet, followed by manageable and those in the between-canines easy-fit categories. In contrast, the C. melanocephalus diet was dominated by hand manageable and between-canines difficultfit categories. Fruit category selection differences between C. melanocephalus and the other taxa analysed were attributed to body size and habitat composition.