RESUMO
Understanding diet selectivity is a longstanding goal in primate ecology. Deciphering when and why primates consume different resources can provide insights into their nutritional ecology as well as adaptations to food scarcity. Plant pith, the spongy interior of plant stems, is occasionally eaten by primates, but the context is poorly understood. We examine the ecological, mechanical, chemical, and nutritional basis of plant pith selection by a wild, frugivorous-omnivorous primate (Cebus imitator). We test the hypothesis that pith is a fallback food, that is, consumed when fruit is less abundant, and test for differences between plant species from which pith is eaten versus avoided. We collected 3.5 years of capuchin pith consumption data to document dietary species and analyzed "pith patch visits" in relation to fruit availability, visits to fruit patches, and climatic seasonality. We analyzed dietary and non-dietary species for relative pith quantity, mechanical hardness, odor composition, and macronutrient concentrations. Capuchins ate pith from 11 of ~300 plant species common in the dry forest, most commonly Bursera simaruba. We find that pith consumption is not directly related to fruit availability or fruit foraging but occurs most frequently (84% of patch visits) during the months of seasonal transition. Relative to common non-dietary species, dietary pith species have relatively higher pith quantity, have softer outer branches and pith, and contain more terpenoids, a class of bioactive compounds notable for their widespread medicinal properties. Our results suggest that greater pith quantity, lower hardness, and a more complex, terpenoid-rich odor profile contribute to species selectivity; further, as pith is likely to be consistently available throughout the year, the seasonality of pith foraging may point to zoopharmacognosy, as seasonal transitions typically introduce new parasites or pathogens. Our study furthers our understanding of how climatic seasonality impacts primate behavior and sheds new light on food choice by an omnivorous primate.
RESUMO
Studying fruit traits and their interactions with seed dispersers can improve how we interpret patterns of biodiversity, ecosystem function and evolution. Mounting evidence suggests that fruit ethanol is common and variable, and may exert selective pressures on seed dispersers. To test this, we comprehensively assess fruit ethanol content in a wild ecosystem and explore sources of variation. We hypothesize that both phylogeny and seed dispersal syndrome explain variation in ethanol levels, and we predict that fruits with mammalian dispersal traits will contain higher levels of ethanol than those with bird dispersal traits. We measured ripe fruit ethanol content in species with mammal- (n = 16), bird- (n = 14) or mixed-dispersal (n = 7) syndromes in a Costa Rican tropical dry forest. Seventy-eight per cent of fruit species yielded measurable ethanol concentrations. We detected a phylogenetic signal in maximum ethanol levels (Pagel's λ = 0.82). Controlling for phylogeny, we observed greater ethanol concentrations in mammal-dispersed fruits, indicating that dispersal syndrome helps explain variation in ethanol content, and that mammals may be more exposed to ethanol in their diets than birds. Our findings further our understanding of wild fruit ethanol and its potential role as a selective pressure on frugivore sensory systems and metabolism.