Plant traits associated with seed dispersal by ducks and geese in urban and natural habitats

Abstract

Ducks and geese are little studied dispersal vectors for plants lacking a fleshy fruit, and our understanding of the traits associated with these plants is limited. We analyzed 507 faecal samples of mallard (Anas platyrhynchos) and Canada goose (Branta canadensis) from 18 natural and urban wetlands in England, where they are the dominant resident waterfowl. We recovered 930 plant diaspores from 39 taxa representing 18 families, including 28 terrestrial and five aquatic species and four aliens. Mallards had more seeds and seed species per sample than geese, more seeds from barochory and hydrochory syndromes, and seeds that on average were larger and from plants with greater moisture requirements (i.e., more aquatic). Mallards dispersed more plant species than geese in natural habitats. Plant communities and traits dispersed were different between urban (e.g., more achenes) and natural (e.g., more capsules) habitats. Waterfowl can readily spread alien species from urban into natural environments but also allow native terrestrial and aquatic plants to disperse in response to climate heating or other global change. Throughout the temperate regions of the Northern Hemisphere, the mallard is accompanied by a goose (either the Canada goose or the greylag goose) as the most abundant waterfowl in urbanized areas. This combination provides a previously overlooked seed dispersal service for plants with diverse traits.

The dispersal potential of endangered plants versus non‐native garden escapees

“…The higher rate of wind-dispersed species among endangered native plants may be particularly beneficial in urban to rural contexts due to human mobility infrastructure and wind from passing vehicles, fostering an increased likelihood of dispersing to novel urban or natural remnant habitats (Planchuelo et al, 2020;von der Lippe & Kowarik, 2008). Endozoochory likely serves as another important dispersal avenue in urban green spaces (Tóth et al, 2023), which can foster a high diversity of animals, such as birds (Davies et al, 2009).…”

“…Studies show, for example, that endangered species, such as orchids can thrive along roadsides and in the neo-habitats humans create (Fekete et al, 2020;Rewicz et al, 2017). Similarly, numerous animals use human-made habitats, such as gardens and ponds, and can effectively disperse native plants from urban areas to natural ecosystems (Tóth et al, 2023). My analysis indicates that, based on dispersal ecological differences alone, there is no inherent reason why endangered native plants, especially those suited to gardening, should not benefit from these types of dispersal.…”

“…Thus, not only zoochory by humans but also zoochory by animals, especially endozoochory, that is, the transport of seeds by the ingestion of animals, is probably an important means of dispersal away from urban and rural green spaces (e.g. Tóth et al, 2023).…”

“…Seed stickiness, hooks or barbs may enhance attachment and facilitate dispersal by humans (Auffret & Cousins, 2013;Ridley, 1930;Wichmann et al, 2009). Also, floating devices like balloon structures can make seeds more accessible to waterbirds in garden ponds, aiding in endozoochory (Tóth et al, 2023). Nutrient-rich structures may increase seed ingestion, also promoting endozoochory.…”