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 33 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 65% 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

Gut travellers: Internal dispersal of aquatic organisms by waterfowl

Little is known about the role of migratory waterfowl in the long-distance dispersal (LDD) of seeds. We studied the gut contents of 42 teals Anas crecca collected in the Camargue, southern France, and found intact seeds of 16 species. There was no relationship between the probability that a given seed species was found intact in the lower gut, and the seed hardness or size. The number of seeds found in the oesophagus and gizzard (a measure of ingestion rate) was the only significant predictor of the occurrence of intact seeds in the lower gut, so studies of waterfowl diet can be used as surrogates of dispersal potential. In a literature review, we identified 223 seed species recorded in 25 diet studies of teal, pintail Anas acuta, wigeon A. penelope or mallard A. platyrhynchos in Europe. We considered whether limited species distribution reduces the chances that a seed can be carried to suitable habitat following LDD. Overall, 72% of plant species recorded in duck diets in southern Europe (36 of 50) were also recorded in the north, whereas 97% of species recorded in duck diets in the north (137 of 141) were also recorded in the south. This suggests a great potential for LDD, since most dispersed plants species occur throughout the migratory range of ducks. Migratory ducks are important vectors for both terrestrial and aquatic plant species, even those lacking the fleshy fruits or hooks typically used to identify seeds dispersed by birds. Finally, we show ducks are important vectors of exotic plant species. We identified 14 alien to Europe and 44 native to Europe but introduced to some European countries whose seeds have been recorded in duck diet.

The role of migratory ducks in the long‐distance dispersal of native plants and the spread of exotic plants in Europe

The study was funded by ESF - EURODIVERSITY project BIOPOOL. DSV was supported by the Fundacao para a Ciencia e Tecnologia grant SFRH/BD/48091/2008, co-financed by the European Social Fund (ESF)

Migratory strategies of waterbirds shape the continental-scale dispersal of aquatic organisms

Summary
Dabbling ducks (Anatinae) are omnivorous birds that are widespread, numerous, highly mobile and often migratory, and therefore have great potential for (long distance) dispersal of other organisms, including plants. However, their ability to act as plant dispersal vectors has received little attention compared to frugivores and is often assumed to be relevant only for wetland species.
To evaluate the potential for plant dispersal by dabbling ducks, we collated and analysed existing data. We identified all plant species whose seeds have been recorded in the diets of the seven dabbling duck (Anas) species in the Western Palaearctic, as reported from gut content analyses. We then analysed the habitats and traits of these plant species to identify general patterns, and related these to data on gut passage survival and duck movements.
A large number of plant species (> 445 species of 189 genera and 57 families) have been recorded in the diet of dabbling ducks. These plant species represent a very wide range of habitats, including almost the full range of site fertility, moisture and light conditions, excluding only very dry and deeply shaded habitats. The ducks prefer seeds of intermediate sizes (1–10 mm3), which have good chances to survive gut passage, but also ingest smaller and larger seeds. Ingested seeds represent a wide range of dispersal syndromes, including fleshy fruits. Many species (62%) were not previously considered animal-dispersed in plant data bases, and 66% were not identified as bird-dispersed. Rarefaction analyses suggest that our analysis still greatly underestimates the total number of plant species ingested.
Synthesis. Dabbling ducks do not exclusively ingest seeds of wetland plants, which make up only 40% of the ingested species. Rather, they feed opportunistically on a wide cross-section of plant species available across the landscapes they inhabit. Given the millions of ducks, the hundreds to thousands of seeds ingested per individual on a daily basis, and known gut passage survival rates, this results in vast numbers of seeds dispersed by ducks per day. Internal seed dispersal by dabbling ducks appears to be a major dispersal pathway for a far broader spectrum of plant species than previously considered.

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Seed dispersal by dabbling ducks: an overlooked dispersal pathway for a broad spectrum of plant species

The importance of waterbirds as vectors of aliens has been recognized since Darwin's time, yet research by pioneers has been forgotten during the development of modern invasion biology, which tends to overlook this means of dispersal. Waterbirds are ignored in databases of alien species and invasion pathways, making management and prevention of invasions more difficult. I summarize 22 studies that provide empirical evidence for the dispersal of alien plants and invertebrates by waterbirds in aquatic and terrestrial ecosystems, complementing 14 studies recently identified by Reynolds et al. (2015, Diversity and Distributions, 21, 744–754). Together, these studies provide empirical evidence for the dispersal of 79 alien plant species and eight alien invertebrates by waterbirds, including some of the worst aquatic invaders and the most widely distributed alien terrestrial plant species. Waterbirds known to be vectors include ducks, geese, swans, shorebirds, gulls, herons and rails. Aliens are usually dispersed after being ingested or becoming attached to plumage, bills or feet, but waterbirds also disperse alien species when making nests, when preying on other vectors such as fish, or even attached to leg rings. Whilst waterbirds may have a trivial role in explaining the arrival of alien species to new continents, they have a vital role in spreading aliens around once they get there. Greater focus on the role of waterbird vectors is essential if management of invasions is to be effective, and I make proposals for future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/ddi.12392

The importance of waterbirds as an overlooked pathway of invasion for alien species.

Seed dispersal is an important process for plants, but may be particularly important for plants occurring in spatially isolated habitats like wetlands. Variation in the geographic distribution of wetland plant species may be strongly influenced by their ability to use waterbirds, particularly waterfowl to enhance dispersal. We used controlled feeding and germination experiments to investigate recovery, retention time, and germination for the seeds of 10 wetland plant species (Chenopodium album, Digitaria ischaemum, Echinochloa colonum, Echinochloa crusgalli, Eleocharis palustris, Panicum dichotomiflorum, Polygonum lapathifolium, Polygonum pensylvanicum, Rumex crispus, and Scheonoplectus maritimus) and compared how these metrics varied with seed characteristics. We fed a known number of seeds to captive raised mallards (Anas platyrhynchos) and collected fecal samples every 4 hours for 48 hours; all recovered seeds were planted in seedling trays and watched for 60 days to monitor germination. We co...

https://bioone.org/journals/wetlands/volume-28/issue-2/07-101.1/Dispersal-of-wetland-plant-seeds-by-mallards--influence-of/10.1672/07-101.1.pdf

Chanpen Wongsriphuek

Papers

Dispersal of wetland plant seeds by mallards: influence of gut passage on recovery, retention, and germination