How frequent is external transport of seeds and invertebrate eggs by waterbirds? A study in Doñana, SW Spain

Vertebrates are important seed dispersers for many plants. In addition to of seeds, ingestion often affects the proportion or rate of seed germination. present one of the first studies comparing the effects of different waterbird species the seeds of a subcosmopolitan pondweed, Potamogeton pectinatus. We also present first comparison of the effects of digestion by ducks (mallard Anas platyrhynchos, A. clypeata and wigeon A. penelope) and physical-chemical “simulation digestion” on pondweed seed germination. In two experiments differing in the of the preceding stratification period, two to three individuals per duck species force-fed 150 seeds each. Average retrieval, total germination and germination did not differ significantly between duck species. Germination rate was higher for ingested seeds, intermediate for scarified seeds (i.e. after mechanical removal of epicarp+mesocarp) and lowest for the controls and acid treated seeds, independently the length of the stratification period. Total germination, however, did not differ among duck-ingested, scarified, control and acid treated seeds. Consequently changes in germination rate after ingestion by ducks seem related to the treatment in the gut and unrelated to exposure to acidic conditions. The coexistence ingested and uningested seeds within a given seed cohort will increase the of seed germination patterns, which can favour the colonisation of habitats by unpredictable environmental conditions.