Data from: Bird-mediated seed dispersal: reduced digestive efficiency in active birds modulates the dispersal capacity of plant seeds

Plant populations in fragmented ecosystems rely largely on internal dispersal by animals. To unravel the mechanisms underlying this mode of dispersal, an increasing number of experimental feeding studies is carried out. However, while physical activity is known to affect vertebrate digestive processes, almost all current knowledge on mechanisms of internal seed dispersal has been obtained from experiments with resting animals. We investigated how physical activity of the mallard Anas platyrhynchos, probably the quantitatively most important biotic dispersal agent in aquatic habitats in the entire Northern Hemisphere, affects gut passage survival and retention time of ingested plant seeds. We fed seeds of nine common wetland plants to mallards trained to subsequently swim for six hours in a flume tank at different swimming speeds (activity levels). We compared gut passage survival and retention times of seeds against a control treatment with mallards resting in a conventional dry cage. Intact gut passage of seeds increased significantly with mallard activity (up to 80% in the fastest swimming treatment compared to the control), identifying reduced digestive efficiency due to increased metabolic rates as a mechanism enhancing the dispersal potential of ingested seeds. Gut passage speed was modestly accelerated (13% on average) by increased mallard activity, an effect partly obscured by the interaction between seed retention time and probability of digestion. Gut passage acceleration will be more pronounced in digestion-resilient seed species, thereby modulating their dispersal distances. Our findings imply that seed dispersal potential by mallards calculated from previous experiments with resting birds is highly underestimated, while dispersal distances may be overestimated for some plant species. Similar effects of physical activity on digestive efficiency of mammals suggests that endozoochorous dispersal of plant seeds by vertebrates is more effective and plays a quantitatively more important ecological role in both terrestrial and aquatic ecosystems than previously thought.

破碎化生态系统中的植物种群，在很大程度上依赖动物介导的内部传播。为阐明这类传播模式背后的潜在机制，相关实验性饲喂研究的数量正持续增长。然而，尽管学界已证实物理活动会影响脊椎动物的消化过程，但目前关于种子体内传播机制的几乎所有认知，均来自对静止状态动物开展的实验。
本研究聚焦绿头鸭（Anas platyrhynchos）——其大概率是全球北半球水生栖息地中定量层面最为关键的生物传播媒介——探究其物理活动水平对摄入植物种子的肠道通过存活率（gut passage survival）与滞留时间（retention time）的影响。
我们将9种常见湿地植物的种子饲喂给经训练的绿头鸭，这些个体可在不同游泳速度（即活动水平）的流水槽（flume tank）中游动6小时；同时设置对照组，让绿头鸭在常规干燥笼舍中静止休息，以此对比两组的种子肠道通过存活率与滞留时间。
实验结果显示，随着绿头鸭活动量提升，种子的完整肠道通过比例显著升高：最快游泳组的完整通过比例最高可达对照组的80%。这表明代谢率提升所导致的消化效率降低，是提升摄入种子传播潜力的关键机制之一。
绿头鸭活动量增加会小幅加快肠道通过速度（平均提升13%），但该效应部分被种子滞留时间与消化概率之间的交互作用所掩盖。肠道通过速度的加快在耐消化的种子物种中会更为显著，进而调节其传播距离。
本研究结果提示，基于此前针对静止鸟类开展的实验所估算的绿头鸭种子传播潜力，存在显著低估；而部分植物物种的传播距离则可能被高估。物理活动对哺乳动物消化效率的类似影响表明，脊椎动物介导的植物种子体内动物传播（endozoochorous dispersal），其实际传播效果更为显著，且在陆地与水生生态系统中发挥的定量生态学作用，也较此前的认知更为重要。