Effect of ingestion by five avian dispersers on the retention time, retrieval and germination of Ruppia maritima seeds

1. Vertebrates are important seed dispersers for many plants, particularly those inhabiting naturally fragmented habitats such as lakes and wetlands. Such dispersal often takes place through the transport of ingested seeds (endozoochory). 2. Endozoochorous passage of seeds is likely to vary among both disperser and dispersed species. We hypothesized that seed retention time and survival of gut passage varies among disperser species (here Anas ducks) and is influenced by intraspecific differences in seed size. 3. Wigeongrass (Ruppia maritima) seeds were ingested by five duck species; Teal, Wigeon, Shoveler, Pintail and Mallard. Defecated seeds were recovered and germinated. 4. Total retrieval and germination of seeds, patterns of retrieval over time and seed weight before and after gut passage did not differ among duck species. Hence interspecific differences among Anas ducks and intraspecific differences in seed weight do not affect seed retention time or the response of seeds to gut passage. 5. Germination of retrieved seeds was influenced by the retention time in the gut, with seeds voided earlier more likely to germinate than those voided later. 6.The probability of dispersal at different retention times by any given duck was low. However, when considering the thousands of ducks moving among wetlands, the dispersal probabilities of seeds become significant. 7.Estimation of seed dispersal distance as a function of retention time suggested higher dispersal probabilities for seeds voided earlier. Based on average flight speeds ranging from 10 to 70 km h(-1), most probable dispersal distances range from 40 to 280 km. Dispersal over greater distances is possible, but less likely.