Data from: Interactions between seed traits and digestive processes determine the germinability of bird-dispersed seeds

Waterbirds disperse a wide range of plant seeds via their guts, promoting biotic connectivity between isolated habitat patches. However, the intensity of digestive forces encountered by seeds, and therefore their potential to survive digestive tract passage, varies within and between waterbird species. Here, we investigate under controlled conditions how the interaction between seed traits and digestive strategies affect the germinability of seeds following waterbird-mediated dispersal. We exposed seeds of 30 wetland plant species to the main digestive processes in the dabbling duck digestive system: mechanical, chemical and intestinal digestion. These were simulated by 1) a pressure test and scarification treatment, 2) incubation in simulated gastric juice, and 3) incubation in intestinal contents of culled mallards (Anas platyrhynchos). We evaluated their separate and combined effects on seed germination, and identified the role of seed size and seed coat traits in resisting the digestive forces. Seeds were generally resistant to separate digestive processes, but highly sensitive to a combination. Resistance to mechanical break-down was reduced by up to 80% by chemical pre-treatment, especially for seeds with permeable coats. Scarified seeds were 12–17% more vulnerable to chemical and intestinal digestive processes than undamaged seeds. Large seeds and seeds with thin, permeable coats were particularly sensitive to chemical and intestinal digestion. These results indicate that efficient digestion of seeds requires multiple digestive processes. The gizzard, responsible for mechanical digestion, plays a key role in seed survival. Omnivorous birds, which have relatively light gizzards compared to pure herbivores or granivores, are thus most likely to disperse seeds successfully. Regardless of digestive strategy, small seeds with tough seed coats are most resistant to digestion and may be adapted to endozoochorous dispersal by waterbirds.水禽（waterbird）可通过消化道传播多种植物种子，促进孤立生境斑块间的生物连通性。然而，种子所承受的消化作用力强度——进而决定其经消化道存活的潜力——在水禽物种内部及不同物种间均存在差异。本研究在可控实验条件下，探究了种子性状与消化策略的交互作用如何影响水禽介导传播后种子的发芽率（germinability）。我们选取30种湿地植物的种子，模拟钻水鸭（dabbling duck）消化系统的三类核心消化过程：机械消化、化学消化与肠道消化。具体模拟方案为：1）压力测试与种皮划痕处理；2）在模拟胃液中孵育；3）在宰杀的绿头鸭（Anas platyrhynchos）肠道内容物中孵育。我们评估了这三类过程单独及联合作用对种子萌发的影响，并明确了种子尺寸与种皮性状在抵御消化作用力中的功能。整体而言，种子对单一消化过程通常具有抗性，但对联合消化过程则极为敏感。化学预处理可使种子抗机械破碎的能力最高降低80%，对于种皮通透的种子效果尤为显著。经种皮划痕处理的种子，其对化学与肠道消化过程的敏感性较未受损种子高出12%~17%。尺寸较大、种皮薄且通透的种子对化学与肠道消化过程尤为敏感。本研究结果表明，高效的种子消化需要多类消化过程协同作用。负责机械消化的肌胃（砂囊，gizzard）在种子存活过程中发挥关键作用。相较于专性草食动物或食谷动物，杂食性鸟类的肌胃相对较轻，因此其成功传播种子的可能性最高。无论消化策略如何，种皮坚硬的小型种子对消化的抗性最强，这类种子或已适应通过水禽进行体内动物传播（endozoochorous dispersal）。