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Integration of exotic seeds into an Azorean seed dispersal network

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Abstract

Seed dispersal plays a central role in plant ecology. Among animals, birds are particularly important seed dispersers, often incorporating exotic plants into their diets and facilitating their integration in the communities. Network theory offers a highly informative framework to study the structural and functional attributes of complex interactions networks. We used information from bird fecal samples to build a quantitative seed dispersal network for the last fragment of native laurel forest in the island of São Miguel—Azores with three specific objectives: (1) to assess the integration of exotic seeds into seed dispersal; (2) to evaluate the impact of exotic plants in network structure; (3) to test the potential of an exotic species to reduce the seed dispersal of a co-occurring native, via competition for seed dispersers. The seed dispersal network was based on the analysis of 1,121 droppings and described 74 unique interactions between 41 plant species and 7 bird species. Exotic seeds deeply infiltrated into the seed dispersal network forming the majority (59 %) of seeds in the droppings and including those of three globally invasive plants. Overall, birds depended equally on native and exotic fruits despite the lower abundance of the latter in the study area. In an experiment, birds did not show a preference for fruits of the exotic Leycesteria formosa over the native Vaccinium cylindraceum consuming them equally. However, the presence of the exotic plant negatively affected the number of native seeds dispersed, by diverting some of the consumers of the native fruits. Taken altogether the results reveal an alarming invasion level of seed dispersal systems in one of the last remnant native forests of the Azores.

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Acknowledgments

We thank the LIFE-Priolo team, particularly Ricardo Ceia, Hugo Sampaio, Carlos Silva and Sandra Parejo for all the logistic support in the field, Márcia Santos, Bronwen Lester and Catarina Heleno for help during fieldwork, and Rachel Gibson and Mariano Devoto for sharing R code.

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Authors and Affiliations

  1. Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, P.O. Box 3046, 3001-401, Coimbra, Portugal

    Ruben H. Heleno

  2. Institute of Marine Research (IMAR/CMA), Department of Life Sciences, University of Coimbra, Coimbra, Portugal

    Jaime A. Ramos

  3. School of Biological Sciences, University of Bristol, Bristol, UK

    Jane Memmott

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  1. Ruben H. Heleno
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  2. Jaime A. Ramos
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  3. Jane Memmott
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Correspondence to Ruben H. Heleno.

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Heleno, R.H., Ramos, J.A. & Memmott, J. Integration of exotic seeds into an Azorean seed dispersal network. Biol Invasions 15, 1143–1154 (2013). https://doi.org/10.1007/s10530-012-0357-z

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