Seed dispersal by waterfowl

Background/Question/Methods

As recognized by Darwin in the Origin of Species, dispersal by migratory waterbirds can explain the extremely wide distribution of many species of aquatic plants and invertebrates, many of which occur both in the breeding and wintering areas used by a migratory population. However, the study of seed dispersal by vertebrates has focused mainly on plants with flesh fruits dispersed in terrestrial systems. In recent years, there has been growing attention  to dispersal by waterfowl of seeds from plants lacking fleshy fruits. We review our current understanding of global patterns of seed dispersal by waterfowl, based on the literature and on unpublished data and analyses. We also consider the value of such dispersal as an ecosystem service.

Results/Conclusions

Darwin underestimated the ability of seeds to be transported inside the guts of waterbirds, and recent studies suggest that endozoochory is a more important process than epizoochory/ectozoochory. Migratory Anatidae and shorebirds are major vectors of long-distance dispersal, and seeds of most plant taxa survive gut passage at a high rate. As well as aquatic plants, waterfowl disperse seeds of a broad range of terrestrial plants from watersheds, and many of these plants have previously been assumed to have very different dispersal modes over a shorter range. This brings into question the assumption that dispersal mode is predictable from seed morphology, which underlies much literature (e.g. comparing dispersal modes between floras of different biogeographical regions).  Seed dispersal by waterfowl is likely to play a vital role in the changes in species distributions and population genetics which can be expected as a response to global change such as climate warming. Many new waterbodies are being created worldwide, partly to mitigate against destruction and degradation of natural waterbodies.  Colonization of these new wetlands by plants carried by waterfowl is an ecosystem service likely to be of significant value. On the other hand, waterfowl can and do promote the spread of alien species, and their role as vectors should be taken into account when considering how to prevent and manage biological invasions. We outline priorities for future research.