Seed dispersal by waterbirds: a mechanistic understanding by simulating avian digestion

Waterbirds disperse plant species via ingestion and egestion of seeds (endozoochory). However, our understanding about the regulating effects seed traits, underlying mechanisms possible (co)evolutionary processes is limited by traditional reliance on data from feeding experiments with living waterbirds. Here, we overcome these limitations developing applying a new bioassay that realistically simulates digestive for Anseriformes We test three hypotheses: 1) survival germination are most affected mechanical digestion in waterbird gizzard; 2) size, hardness, imbibition shape regulate survival; 3) plants growing aquatic habitats benefit endozoochory Experiments 28 200 48 demonstrated species-specific was entirely determined avian gizzard. Intestinal did not affect but establishment (germinability time) 21% species. Large, hard survived simulations best, contrast to generally higher smaller during vivo experiments. This mechanistically explains small escape rather than being inherently more resistant (the ‘escape mechanism'), while large retained until fully digested or regurgitated ‘resistance regurgitation mechanism'). Plants wetter had similar survival, stimulated their germinability accelerated terrestrial plants. indicates relative advantage wet habitats, possibly reflecting co-evolutionary response related dormancy breaking gut passage. Simulating passage using allowed establishing identifying relevant traits involved dispersal information enhances how animal distributions, which extremely now current anthropogenic pressures already severely impact capacities.