Data from: Great cormorants reveal overlooked secondary dispersal of plants and invertebrates by piscivorous waterbirds

In wetland ecosystems, birds and fish are important dispersal vectors for plants and invertebrates, but the consequences of their interactions as vectors are unknown. Darwin suggested that piscivorous birds carry out secondary dispersal of seeds and invertebrates via predation on fish. We tested this hypothesis in the great cormorant (Phalacrocorax carbo L.). Cormorants regurgitate pellets daily, which we collected at seven European locations and examined for intact propagules. One-third of pellets contained at least one intact plant seed, with seeds from 16 families covering a broad range of freshwater, marine and terrestrial habitats. Of 21 plant species, only two have an endozoochory dispersal syndrome, compared with five for water and eight for unassisted dispersal syndromes. One-fifth of the pellets contained at least one intact propagule of aquatic invertebrates from seven taxa. Secondary dispersal by piscivorous birds may be vital to maintain connectivity in meta-populations and between river catchments, and in the movement of plants and invertebrates in response to climate change. Secondary dispersal pathways associated with complex food webs must be studied in detail if we are to understand species movements in a changing world.

在湿地生态系统中，鸟类与鱼类是植物及无脊椎动物的重要扩散媒介（dispersal vector），但二者作为扩散媒介的交互作用所带来的生态后果尚不明确。达尔文曾提出，食鱼鸟类可通过捕食鱼类完成植物种子与无脊椎动物的二次扩散。我们以普通鸬鹚（Phalacrocorax carbo L.）为研究对象对该假说进行了验证。普通鸬鹚每日会反刍吐出食丸（pellets），我们在欧洲7处采样点收集了这些食丸并检测其中的完整繁殖体（propagules）。结果显示，三分之一的食丸中至少含有一粒完整的植物种子，涉及16个植物科，涵盖淡水、海洋与陆生多种生境。在21种被检测的植物中，仅2种具有体内动物传播（endozoochory）扩散综合征（dispersal syndrome），另有5种依赖水体传播，8种为无辅助扩散。五分之一的食丸中至少含有一个来自7个类群的水生无脊椎动物完整繁殖体。食鱼鸟类介导的二次扩散或许对维持集合种群（meta-populations）的连通性、河流流域间的物种连接，以及植物与无脊椎动物响应气候变化的迁移活动至关重要。若要理解气候变化背景下的物种迁移规律，我们亟需深入研究与复杂食物网相关的二次扩散路径。