Maximization of energy or nutrient balancing: the interplay between fruit chemical content and foraging behaviour in fruit-eating birds

PEDRO G. BLENDINGER; IRENE BENDER; SILVIA B. LOMASCOLO; JULIETA MAGRO; MARIANO ORDANO; MARÍA G. NUÑEZ-MONTELLANO; ANDRES F. RAMIREZ-MEJIA; TOBIAS N. ROJAS; ROMÁN A. RUGGERA; MARIANA VALOY

Corbett Landscape

Simposio; 7th Frugivores and seed dispersal symposium; 2020

The fruit diet of frugivores is driven by foraging strategies of energy maximization or nutrient balancing. However, frugivores face a changing fruit market when they make foraging decisions. It is well known that the amount of available fruits and phenotypic trait matching impose filters on the fruit diet, but less is known about the role of foraging decisions of the fruit chemical content. The differences between fruit species in pulp quantity and chemical quality can interact with behavioural, morphological and physiological traits of the consumers, determining the contribution of the fruit species to the provision of nutrients and energy. We use extensive field and laboratory data and modelling to explore whether a fruit-based diet can provide energy and nutrients necessary for frugivores, as well as its variation between functional types of frugivores. Using the Resource Provisioning Effectiveness (RPE) framework we investigate the effectiveness of consumed fruit species to provide daily requirements of energy to Andean birds, and compare them with the composition of field diets. Similarly, we use Nutritional Geometry (NG) framework to assess the adjustment of field fruit diets to a theoretical diet balanced in macronutrients. We use diet data of ca. 35 bird species from different sites and seasons, chemical data of ca. 40 species of fruits; we model the daily ingestion rate of each fruit species for each frugivore, and estimate their energy assimilation and macronutrient balancing in the diets. Then, we assess how fruit RPEs and balances depend on the bird's fruit handling behaviour, body size and specialization, and the adjustment of the diet to energy maximization (in terms of RPE) and nutrient balancing (in terms of NG) strategies. We provide valuable information on how fruit chemical composition interacts with the ability of the frugivores to acquire pulp, determining the foraging decisions and the composition of the fruit diet.