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Functional importance of avian seed dispersers changes in response to human-induced forest edges in tropical seed-dispersal networks

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Abstract

Although seed-dispersal networks are increasingly used to infer the functioning of ecosystems, few studies have investigated the link between the properties of these networks and the ecosystem function of seed dispersal by animals. We investigate how frugivore communities and seed dispersal change with habitat disturbance and test whether relationships between morphological traits and functional roles of seed dispersers change in response to human-induced forest edges. We recorded interaction frequencies between fleshy fruited plants and frugivorous bird species in tropical montane forests in the Bolivian Andes and recorded functional bird traits (body mass, gape width and wing tip length) associated with quantitative (seed-removal rate) and qualitative (seed-deposition pattern) components of seed-dispersal effectiveness. We found that the abundance and richness of frugivorous birds were higher at forest edges. More fruits were removed and dispersed seeds were less clustered at edges than in the interior. Additionally, functional and interaction diversity were higher at edges than in the interior, but functional and interaction evenness did not differ. Interaction strength of bird species increased with body mass, gape width and wing tip length in the forest interior, but was not related to bird morphologies at forest edges. Our study suggests that increases in functional and interaction diversity and an even distribution of interaction strength across bird morphologies lead to enhanced quantity and tentatively enhanced quality of seed dispersal. It also suggests that the effects of species traits on ecosystem functions can vary along small-scale gradients of human disturbance.

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Acknowledgments

We are grateful to Rodrigo Calvimontes, Fabrizzio Peralta, and especially to Veronica Avalos, for their help during fieldwork, to the staff of the Herbario Nacional de Bolivia for their help with the identification of plant species and to R. van den Elzen (Zoologisches Forschungsmuseum Alexander Koenig, Bonn), R. Prŷs-Jones and M. P. Adams (Natural History Museum, Tring), G. Mayr (Senckenberg Museum, Frankfurt/M.) and R. Winkler (Naturhistorisches Museum, Basel) for providing access to the bird collections kept in their charge. M. Hennen, J. Bates and D. Willard [Field Museum of Natural History (FMNH), Chicago] sent specimens, and J. V. Remsen and S. W. Cardiff (Louisiana State University Museum of Natural Science, Baton Rouge) and D. Willard (FMNH, Chicago) provided additional measurements. We also thank R. Diesener, S. Frahnert, C. Bracker, P. R. Becker, J. Fjeldså, N. Krabbe and J. Mlíkovsky for information about collection holdings. The study was funded by the German Science Foundation (Deutsche Forschungsgemeinschaft) (HE2041/20-1). M. S. was also supported by the research funding program Landes-Offensive zur Entwicklung Wissenschaftlich-ökonomischer Exzellenz of Hesse’s Ministry of Higher Education, Research and the Arts. This study was done under permission and current laws of the government of Bolivia.

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Correspondence to Francisco Saavedra.

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Communicated by Joanna E. Lambert.

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Saavedra, F., Hensen, I., Beck, S.G. et al. Functional importance of avian seed dispersers changes in response to human-induced forest edges in tropical seed-dispersal networks. Oecologia 176, 837–848 (2014). https://doi.org/10.1007/s00442-014-3056-x

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