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Front. Ecol. Evol. | doi: 10.3389/fevo.2018.00018

The Strength and Drivers of Bird-mediated Selection on Fruit Crop Size: A Meta-Analysis

Facundo X. Palacio1, 2* and  Mariano Ordano2
  • 1Sección Ornitología, División Zoología de Vertebrados, Facultad de Ciencias Naturales y Museo Universidad Nacional de La Plata, Argentina
  • 2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Fundación Miguel Lillo and Unidad Ejecutora Lillo (UEL-FML-CONICET), Argentina

In seed-dispersal mutualisms, the number of fruit a plant displays is a key trait, as it acts as a signal for seed dispersers that entails fruit removal and exportation of reproductive units (fruit crop size hypothesis). Although this hypothesis has gained general acceptance, forces driving the shape and strength of natural selection exerted by birds on fruit crop size remains an unresolved matter. Here, we propose that ecological filters promoting high functional equivalence of interacting partners (similar functional roles) translate into similar selection pressures on fruit crop size, enhancing selection strength on this trait. We performed a meta-analysis on 50 seed-dispersal systems to test the hypothesis that frugivorous birds exert positive selection pressure on fruit crop size, and to assess whether different factors expected to act as filters (fruit diameter, fruit type, fruiting season length, bird functional groups and latitude) influence phenotypic selection regimes on this trait. Birds promote larger fruit crop sizes as a general pattern in nature. Short fruiting seasons and a high proportion of species belonging to the same functional group showed higher selection strength on fruit crop size. Also, selection strength on fruit crop size increased for large-fruited species and towards the tropics. Our results support the hypothesis that fruit crop size represents a conspicuous signal advertising the amount of reward to visually driven interacting partners, and that both plant and bird traits, as well as environmental factors, drive selection strength on fruit display traits. Furthermore, our results suggest that the relationship among forces impinged by phenology and frugivore functional roles may be key to understand their evolutionary stability.

Keywords: frugivory, Mutualism, phenotypic selection, plant-animal interactions, Seed Dispersal

Received: 20 Oct 2017; Accepted: 14 Feb 2018.

Edited by:

Marco A. Molina-Montenegro, University of Talca, Chile

Reviewed by:

Robert Bagchi, University of Connecticut, United States
Rodrigo S. Rios, University of La Serena, Chile
Constanza C. Neghme, Independent researcher, Spain  

Copyright: © 2018 Palacio and Ordano. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Facundo X. Palacio, Facultad de Ciencias Naturales y Museo Universidad Nacional de La Plata, Sección Ornitología, División Zoología de Vertebrados, Paseo del Bosque s/n, La Plata, 1900, Buenos Aires, Argentina, facundo_palacio@yahoo.com.ar