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The expansion of alien plant species is of global concern, yet our understanding of their dispersal mechanisms is limited. Here we address the potential of alien plant seeds to disperse via ingestion, transport and egestion in waterfowl (endozoochory). Based on their general rapid expansions, we expected alien plant species to have several advantages for endozoochory compared to native plant species. We hypothesised that seeds of alien species would have higher passage rate, longer gut retention times, higher germinability after gut passage and shorter time-to-germination after egestion by waterfowl. In order to test our hypotheses, we compared the endozoochorous dispersal ability of six pairs of congeneric alien and native wetland plant species in a feeding experiment with mallards (Anas platyrhynchos). We focused on differences in seed survival, gut retention time, germinability and time-to-germination. In the analyses we corrected for seed shape and volume as these seed traits are known to have important effects. With gut passage, alien species had higher passage rates and germinated slower, whereas native species had shorter retention times and greater germinability. Controlling for seed traits did not alter these conclusions, but seed traits affected all aspects of the endozoochory process. This suggests that alien species may have particular traits correlated with a higher endozoochory potential. Among control seeds, alien seeds germinated faster and their germinability was higher than natives. Seed traits explained differences in germinability and time-to-germination in control seeds. Seeds of alien plant species have traits that correlate with successful endozoochory. This may provide alien species with a competitive advantage over native plant species by ensuring higher endozoochory rates in new environments, potentially enabling their rapid expansions. Our study underlines the important role of seed traits in the endozoochory potential

Aim: How plants can disperse in response to global change is a critical question, yet major knowledge gaps persist about long-distance dispersal (LDD) mechanisms. We studied the potential a migratory waterfowl has for LDD of flowering plants via gut passage of seeds (endozoochory), comparing spring and autumn migration. Location: United Kingdom and Iceland. Taxon: Pink-footed Goose (Anser brachyrhynchus, Baillon) and Angiosperma. Methods: We studied endozoochory by Pink-footed geese migrating within and between the UK and Iceland by faecal sampling and GPS tracking. We collected 614 faecal samples from 14 areas in the UK and one in Iceland. Using GPS tracks to and from these areas, we estimated how far seeds can be dispersed by Pink-footed geese, and where to or from. Results: We recorded 5507 intact seeds of 35 species (27 terrestrial) from 15 plant families, with lower seed abundance per dropping when birds were migrating northwards in the UK during spring than upon their arrival in autumn. Species richness of plant seeds was highest in Iceland and in autumn. Only four plant species dispersed had an “endozoochory syndrome”. GPS movements showed that seeds retained in guts for up to 24 h can be readily dispersed in both directions between the UK and Iceland, with maximum distances exceeding 2000 km, as well as between UK localities separated by 100 s of km. Movements northwards of ≤400 km were even recorded in autumn. While at stopover sites, daily movements between roost and feeding sites often exceed 20 km. Main Conclusions: Pink-footed geese are LDD vectors for plants previously assumed to lack an LDD mechanism. Spring migration is not the only period when geese move plants to cooler latitudes. The pink-footed goose can allow terrestrial and aquatic plants to cross the ocean and to keep pace with climate change

1. We review progress in our understanding of the importance of waterbirds as dispersal vectors of other organisms, and identify priorities for further research. 2. Waterbirds are excellent for long-distance dispersal (LDD), whereas other vectors such as fish and mammals disperse similar propagules, but over shorter distances. Empirical studies of internal and external transport by waterbirds have shown that the former mechanism generally is more important. Internal transport is widely recognised for aquatic plants and aquatic invertebrates with resting eggs, but also is important for other organisms (e.g., terrestrial flowering plants not dispersed by frugivores, bryophytes, tardigrades, fish eggs). 3. Waterbird vectors also are important in terrestrial habitats, and provide connectivity across terrestrial–aquatic boundaries. There are important differences in the roles of different waterbird species, especially those using different habitats along the aquatic–terrestrial gradient. Early attempts to predict zoochory based on propagule morphology have been found wanting, and more research is needed into how the traits of vectors and vectored organisms (including life history, dormancy and growth traits) explain dispersal interactions. Experimental studies have focused on the potential of propagules to survive internal or external transport, and research into factors determining the establishment success of propagules after dispersal is lacking. 4. Recent spatially explicit models of seed dispersal by waterbirds should be expanded to include invertebrate dispersal, and to compare multiple bird species in the same landscape. Network approaches have been applied to plant–waterbird dispersal interactions, and these are needed for invertebrates. Genetic studies support effective LDD of plants and invertebrates along waterbird flyways, but there remains a lack of examples at a local scale. Next Generation Sequencing and genomics should be applied to waterbird-mediated dis

We review progress in our understanding of the importance of waterbirds as dispersal vectors of other organisms, and identify priorities for further research. Waterbirds are excellent for long-distance dispersal (LDD), whereas other vectors such as fish and mammals disperse similar propagules, but over shorter distances. Empirical studies of internal and external transport by waterbirds have shown that the former mechanism generally is more important. Internal transport is widely recognised for aquatic plants and aquatic invertebrates with resting eggs, but also is important for other organisms (e.g., terrestrial flowering plants not dispersed by frugivores, bryophytes, tardigrades, fish eggs). Waterbird vectors also are important in terrestrial habitats, and provide connectivity across terrestrial–aquatic boundaries. There are important differences in the roles of different waterbird species, especially those using different habitats along the aquatic–terrestrial gradient. Early attempts to predict zoochory based on propagule morphology have been found wanting, and more research is needed into how the traits of vectors and vectored organisms (including life history, dormancy and growth traits) explain dispersal interactions. Experimental studies have focused on the potential of propagules to survive internal or external transport, and research into factors determining the establishment success of propagules after dispersal is lacking. Recent spatially explicit models of seed dispersal by waterbirds should be expanded to include invertebrate dispersal, and to compare multiple bird species in the same landscape. Network approaches have been applied to plant–waterbird dispersal interactions, and these are needed for invertebrates. Genetic studies support effective LDD of plants and invertebrates along waterbird flyways, but there remains a lack of examples at a local scale. Next Generation Sequencing and genomics should be applied to waterbird-med

The cover image is based on the Review Article Dispersal of aquatic and terrestrial organisms by waterbirds: a review of current knowledge and future priorities, by Andy J. Green et al.