Mammalian herbivores can play a role in the endozoochorous dispersal ofProsopisseeds in the arid zones of Argentina, and the introduction of exotic mammals can change relevant parameters of the plant's reproductive ecology. Our specific goals were to quantify the seeds ofProsopis flexuosa,P. chilensisandP. torquatacontained in the faeces of native [mara (Dolichotis patagonum), guanaco (Lama guanicoe)] and exotic [donkey (Equus asinus) and hare (Lepus europaeus)] mammals, and to determine the mortality, germination percentage and germination speed of seeds borne in faeces, compared with those collected from trees. In 2006, seeds were collected directly from trees or removed from mammal faeces. Seeds were counted and classified as apparently healthy or damaged.P. torquataandP. flexuosaseeds were found in the dung of guanaco, hare and mara, whereas onlyP. flexuosaseeds appeared in donkey faeces.P. chilensisseeds were only found in guanaco faeces. There was a notable relative abundance of seeds contained in small herbivore faeces in comparison to the large herbivores. The passage through the digestive tract of animals modified seed germination capacity and speed, with great variability between animal species. Guanacos had greater effects than donkeys on mortality, germination percentage and germination speed. Differences between the effects of both smaller-sized herbivores on seeds were much smaller.

The fate of Prosopis flexuosa seeds dispersed by cattle is dependant on the spatial pattern of dung deposition and foraging movements. We hypothesised that cattle-use site classes explain the response variables related to seed input and fate of seeds, seedlings and saplings (small plants more than one year old). We defined sites with heavy cattle traffic ("trails" and "periphery of trails"), sites used for resting and foraging ("under Prosopis"), and sites where isolated individuals only walk ("under shrubs" and "bare soil"). Considering the established cattle-use site classes, our specific goals were to quantify and compare: (1) seeds transported in cattle dung; (2) seedlings 10 months after dung deposition; (3) established saplings; and (4) germinated and remaining seeds, and seedling survival in dung immediately after dung deposition. In a grazed field at Ñacuñán (Mendoza, Argentina) we worked in four similar areas, each consisting of 25-ha plots 2 km apart. Space use by cattle caused differential seed input: "under Prosopis" and in the "periphery of trails" animals deposited the largest amounts of dung and seeds. Ten months after dung deposition, the highest number of seedlings occurred on "trails", "under Prosopis" and in the "periphery of trails". In the long term, the highest number of established saplings occurred only in the "periphery of trails". The number of seeds germinated immediately after fruit production and dung deposition was very low. Survival of seedlings sprouting from dung-germinated seeds did not exceed one week. On "trails" and in the "periphery of trails" the persistence of seeds in dung was low because of dung disintegration by the action of cattle trampling. The seeds that did not remain in dung were probably the source of seeds that will germinate in the next wet season (i.e. 10 months after dung deposition). With different effects depending on cattle site activity and on the stage of the P. flexuosa plant (seed, seedling, or sapling), defecation and trampling appear to be important processes in the seed dispersal cycle. In this sense, cattle could benefit the establishment of P. flexuosa.

We examined the spatial and social structure of a high-altitude population of the scarcely known southern mountain cavy (Microcavia australis) in Arg