Shorebirds as important vectors for plant dispersal in Europe

Ádám Lovas‐Kiss,José A Alves,Neil E Coughlan,Marta I Sánchez,David M Wilkinson,Andy J Green

doi:10.1111/ecog.04065

Abstract

Shorebirds (Charadriiformes) undergo rapid migrations with potential for long‐distance dispersal (LDD) of plants. We studied the frequency of endozoochory by shorebirds in different parts of Europe covering a broad latitudinal range and different seasons. We assessed whether plants dispersed conformed to morphological dispersal syndromes. A total of 409 excreta samples (271 faeces and 138 pellets) were collected from redshank Tringa totanus, black‐winged stilt Himantopus himantopus, pied avocet Recurvirostra avosetta, northern lapwing Vanellus vanellus, Eurasian curlew Numenius arquata and black‐tailed godwit Limosa limosa in south‐west Spain, north‐west England, southern Ireland and Iceland in 2005 and 2016, and intact seeds were extracted and identified. Godwits were sampled just before or after migratory movements between England and Iceland. The germinability of seeds was tested. Intact diaspores were recovered from all bird species and study areas, and were present in 13% of samples overall. Thirteen plant families were represented, including Charophyceae and 26 angiosperm taxa. Only four species had an ‘endozoochory syndrome’. Four alien species were recorded. Ellenberg values classified three species as aquatic and 20 as terrestrial. Overall, 89% of seeds were from terrestrial plants, and 11% from aquatic plants. Average seed length was higher in redshank pellets than in their faeces. Six species were germinated, none of which had an endozoochory syndrome. Seeds were recorded during spring and autumn migration. Plant species recorded have broad latitudinal ranges consistent with LDD via shorebirds. Crucially, morphological syndromes do not adequately predict LDD potential, and more empirical work is required to identify which plants are dispersed by shorebirds. Incorporating endozoochory by shorebirds and other migratory waterbirds into plant distribution models would allow us to better understand the natural processes that facilitated colonization of oceanic islands, or to improve predictions of how plants will respond to climate change, or how alien species spread.

Highlights

Dispersal is an important determinant of distribution (Ridley 1930), correctly characterising dispersal mechanisms can be crucial in understanding past and future changes in distribution related to ecological and climate changes (Wilkinson 1997, Corlett and Westcott 2013, Tamme et al 2014)
Omnivorous migratory waterbirds can act as important vectors for a wide range of plant species (Figuerola et al 2003, Brochet et al 2009, van Leeuwen et al 2012, Green et al 2016, Lovas-Kiss et al 2018a, b)
More empirical work is needed to establish which plants are dispersed by shorebirds, and other waterbirds, and in what direction, and whether there are plant traits that allow us to make a priori predictions. Such advances in research are necessary if we are to better understand what dispersal mechanisms underlie the colonization of oceanic islands, or the establishment of disjunct distributions

Summary

Introduction

Dispersal is an important determinant of distribution (Ridley 1930), correctly characterising dispersal mechanisms can be crucial in understanding past and future changes in distribution related to ecological and climate changes (Wilkinson 1997, Corlett and Westcott 2013, Tamme et al 2014). Studies examining the dispersal of plants by birds via endozoochory (i.e. dispersal of ingested diaspores that survive gut passage) have mainly focused on frugivorous species (Forget et al 2011, Wenny et al 2016). Omnivorous migratory waterbirds can act as important vectors for a wide range of plant species (Figuerola et al 2003, Brochet et al 2009, van Leeuwen et al 2012, Green et al 2016, Lovas-Kiss et al 2018a, b). There has been relatively little modern interest in their role as vectors of plant dispersal, even though seeds are frequently ingested by most shorebird species (Green et al 2002). Some authors have suggested that shorebirds carry seeds within their plumage or in mud adhering to their feet (i.e. epizoochory; Carlquist 1967, Schenk and Saunders 2017), and field data supports this for microscopic diaspores (Lewis et al 2014, see Coughlan et al 2017 for a review of epizoochory)

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Discussion

Conclusion