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.

水鸟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，以及其因此产生的经消化道通过后存活的潜力，在水鸟物种内部与不同物种间均存在差异。本研究在受控实验条件下，探究种子性状与消化策略的交互作用如何影响水鸟介导传播后的种子萌发能力。我们将30种湿地植物的种子暴露于钻水鸭（dabbling duck）消化系统的三类主要消化过程：机械消化、化学消化与肠道消化。上述过程分别通过以下方式模拟：1）压力测试与种皮划破（scarification treatment）处理；2）模拟胃液孵育；3）使用宰杀绿头鸭（Anas platyrhynchos）的肠道内容物进行孵育。我们评估了各消化过程单独及联合作用对种子萌发的影响，并明确了种子大小与种皮性状在抵御消化作用力中的功能。总体而言，种子对单一消化过程具备较强抗性，但对联合消化过程则极为敏感。化学预处理可使种子抵御机械破碎的能力降低最高达80%，对于种皮通透性较强的种子尤为显著。经种皮划破处理的种子，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%。大种子以及种皮薄、通透性强的种子，对化学与肠道消化过程尤为敏感。上述结果表明，种子要成功经消化道存活，需要多重消化过程协同作用。负责机械消化的肌胃（gizzard）在种子存活过程中发挥关键作用。相较于纯植食性或食谷性鸟类，杂食性鸟类的肌胃相对较轻，因此其最有可能成功传播种子。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，或已适应通过水鸟进行体内传播（endozoochorous dispersal）。