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Gut travellers: internal dispersal of aquatic organisms by waterfowl

Authors

  • Casper H. A. van Leeuwen,

    Corresponding author
    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Animal Ecology and Ecophysiology, Nijmegen, The Netherlands
    2. Radboud University Nijmegen, Institute for Water and Wetland Research, Aquatic Ecology & Environmental Biology, Nijmegen, The Netherlands
    • Aquatic Ecology, Netherlands Institute of Ecology, Royal Netherlands Academy of Arts and Sciences (NIOO-KNAW), Wageningen, The Netherlands
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  • Gerard van der Velde,

    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Animal Ecology and Ecophysiology, Nijmegen, The Netherlands
    2. Naturalis Biodiversity Centre, Leiden, The Netherlands
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  • Jan M. van Groenendael,

    1. Radboud University Nijmegen, Institute for Water and Wetland Research, Aquatic Ecology & Environmental Biology, Nijmegen, The Netherlands
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  • Marcel Klaassen

    1. Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University, Australia
    2. Animal Ecology, Netherlands Institute of Ecology, Royal Netherlands Academy of Arts and Sciences (NIOO-KNAW), Wageningen, The Netherlands
    3. Utrecht University, Landscape Ecology, Utrecht, The Netherlands
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Correspondence: Casper H. A. van Leeuwen, NIOO-KNAW, Droevendaalsesteeg 10, 6708 PB Wageningen, The Netherlands.

E-mail: c.vanleeuwen@nioo.knaw.nl

Abstract

Aim

Patterns of high biodiversity among less mobile organisms throughout isolated locations suggest that passive dispersal importantly contributes to biodiversity. We examined the contribution of waterbirds to the dispersal of plant seeds and macroinvertebrates between aquatic wetlands. Birds are renowned vectors for seeds of terrestrial plants, but less is known about their role in more dispersal-dependent aquatic systems. We therefore performed a meta-analysis on bird-mediated endozoochorous dispersal of aquatic species.

Location

Our review included studies that collected data world-wide.

Methods

We analysed data from 81 peer-reviewed publications on endozoochorous dispersal of aquatic plant seeds and macroinvertebrates by waterbirds.

Results

In total, 36% of 1581 waterbird droppings collected in the field contained one or more intact propagules, with macroinvertebrates found almost as frequently as plant seeds. Positive droppings contained on average 3.3 intact propagules, of which one-third were viable. In 728 trials from 17 published feeding experiments 24% of the ingested propagules were retrieved intact, with c. 6.5% both viable and intact. As many as 17 species of Anatidae and Rallidae were involved in the dispersal of at least 39 species of macroinvertebrates and seeds from 97 species of plants across a wide taxonomic range. Smaller propagules seemed less affected by digestion than larger ones. We provide a first quantitative model that can be used to estimate waterbird-mediated dispersal of propagules between wetlands. This model indicates that an average waterbird has the potential to disperse five viable propagules after flying more than 100 km, and one additional propagule after flying 300 km.

Main conclusions

We demonstrate that waterbirds have the potential to transport a wide variety of aquatic plants and animals over several hundreds of kilometres. High survival of propagules might be explained by propagule adaptations or by the digestive adaptations of birds, whereby energy absorption is thought to be maximized rather than assimilation efficiency. Our meta-analysis suggests that waterbirds might contribute significantly to wetland biodiversity around the world, despite several limitations to our current knowledge. We outline avenues for future research to address these knowledge gaps.

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