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Summary 1.The survival and retention of seeds was studied by feeding known quantities of seeds of 25 species to four captive Fallow Deer (Dama dama L.). To test for ecological correlates, plant species were selected to represent large variation in seed size, seed shape, seed longevity and habitat fertility. 2. Seeds of 24 out of 25 fed plant species survived ingestion and defecation by Fallow Deer. Seed survival ranged between 0·5 and 42% of germinable seeds fed. Time to recover 50% of all seeds defecated by Fallow Deer in faeces averaged 25 h, and ranged from 13 to 38 h. 3. Seed survival was negatively related to seed mass (R = 0·65) and variance of unit seed dimensions (R = −0·56), and positively related to seed longevity (R = 0·40), but not related to habitat fertility. Log 10 of (seed mass × variance of seed dimensions) was the best predictor of seed survival (R = −0·68). 4. The ecological correlates of seed survival presented here can help us to estimate the ability of plant species to disperse seeds over long distances.

Summary1. In this study we aimed to estimate distance distributions of adhesively dispersed seeds and the factors that determine them. 2. Seed attachment and detachment were studied using field experiments with a real sheep, a sheep dummy and a cattle dummy. Seed-retention data were used in correlated random walk models to simulate adhesive seed dispersal. 3. Seed attachment to the sheep dummy was larger in quantity and in number of species, and stronger in relation to seed density in the vegetation, than was seed attachment to the cattle dummy. Species found on the real sheep were also found on the sheep dummy. 4. Detachment from sheep wool differed little between smooth, bristly, small or large seeds, but smooth seeds detached from cattle fur within a few metres. Seeds applied within reach of vegetation detached sooner than seeds applied higher on the dummy. 5. The simulations showed that sheep are long-distance seed-dispersal vectors for seeds of any morphology (99 percentile distance, 2·9 km). The virtual cattle and Fallow Deer dispersed bristly and hooked seeds over long distances (99 percentile distance, 435-840 m), but not smooth seeds. Wood Mouse simulations generated only shortdistance dispersal (99 percentile distance, 12 m).

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Seed dispersal via ingestion and defecation by large herbivores (endozoochory) plays a potentially important role in structuring plant communities. In the present study we tested whether cattle disperse seeds between different plant communities in a heterogeneous coastal habitat. We surveyed the seed contents of cattle dung collected from two habitat types within a grazing system, one in dunes and the other in saltmarsh. The dunes are characterized by sandy soil, and infrequent inundation by the sea, whereas the salt-marsh features clay deposited during inundations. Seeds of both salt-marsh and dune species were dispersed into salt-marsh and dune habitats. The seed content of cattle dung collected in salt-marsh and dunes was similar with respect to species composition and seed density. However, dispersal of dune species into salt-marsh and vice-versa did not result in establishment in those communities. Seed traits per se did not differ between dune species and saltmarsh species. Species abundance in the established vegetation and seed density in dung were positively correlated. Seed abundance for most species found in dung was consistent with the availability of viable seeds during the growing season. Seed mass, seed 'roundness' and seed release height were all negatively correlated with seed numbers in dung. An indirect factor, namely, forage quality of the plant, and hence attractiveness for herbivores, could explain the higher likelihood of seed dispersal of salt-marsh species than of dune species. The salt-marsh harbours species with higher forage quality than the dune species, as derived from Ellenberg nitrogen indicator values.