Abstract
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.
Highlights
Endozoochory is the primary dispersal mode for many plant species and complementary to other dispersal modes for many others [1]
The volume-effect on the resistance against mechanical forces was not altered by acidic pretreatment, but we found a strong role of seed coat strength in the effect of pre-treatment, indicating that seeds with thin and permeable seed coats suffered most from pre-treatment with acid
Our results demonstrate that seeds are generally well resistant against separate digestive processes, as germination rates following scarification, the chemical digestion treatment or the microbial digestion treatment were similar to germination rates of untreated control seeds
Summary
Endozoochory is the primary dispersal mode for many plant species and complementary to other dispersal modes for many others [1]. In freshwater aquatic and surrounding terrestrial habitats, waterbirds, and especially dabbling ducks, disperse a wide range of aquatic, riparian and terrestrial plants [4,5,6]. This dispersal mechanism enables seeds to reach isolated patches in fragmented habitats and helps to maintain biodiversity in degraded landscapes [7]. Large interspecific differences in gut passage survival exist, suggesting that successful endozoochory is mediated by seed size and other less conspicuous traits [11,12,13]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
