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

1. 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.2. We analysed 507 faecal samples of mallard (<i>Anas platyrhynchos</i>) and Canada goose (<i>Branta canadensis</i>) from 18 natural and urban wetlands in England, where they are the dominant resident waterfowl.3.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.4.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.

1. 鸭类与鹅类作为缺乏肉质果实的植物的传播媒介，尚未得到充分研究，学界对这类关联植物的功能性状的认知也较为有限。2. 我们对英格兰境内18处自然与城市湿地的507份绿头鸭（Anas platyrhynchos）和加拿大黑雁（Branta canadensis）的粪便样本开展了分析，这两种鸟类均为当地优势定居水鸟。3. 我们从隶属于18个科的39个类群中，共检出930个植物传播体（plant diaspores），其中包含28种陆生植物、5种水生植物以及4种外来物种。绿头鸭每份样本中的种子数量与种子物种数均高于加拿大黑雁，其粪便中源自重力传播（barochory）与水媒传播（hydrochory）综合征的种子占比更高，且平均种子尺寸更大，来源植物的水分需求更高（即更偏向水生习性）。在自然生境中，绿头鸭传播的植物物种数多于加拿大黑雁。城市生境与自然生境中被传播的植物群落及功能性状存在显著差异：城市生境中瘦果（achenes）占比更高，自然生境中则以蒴果（capsules）居多。4. 水鸟可轻易将外来物种从城市生境扩散至自然环境，同时也能助力本土陆生与水生植物通过扩散以应对气候变暖或其他全球变化问题。在北半球温带区域，绿头鸭常与某一类鹅（加拿大黑雁或灰雁）一同成为城市化地区数量最多的水鸟类群。这一组合为具备多样功能性状的植物提供了此前被忽视的种子传播服务。