Dispersal of aquatic and terrestrial organisms by waterbirds:A review of current knowledge and future priorities

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-mediated dispersal across the landscape. More studies of biogeography, ...