The role of domestic goats in the conservation of four endangered species of cactus: between dispersers and predators

Questions: The aim of this study was to establish the potential of domestic goats to act as cactus seed dispersers by assessing: (1) the proportion of cactus seeds that can pass undamaged through the domestic goat gut, (2) the temporal pattern of seed defecation, (3) whether ingestion by goats enhances or depresses cactus seed germination, and (4) whether the viable cactus seeds contained within goat faecal pellets can germinate directly from the faeces. Location: River basin of Zapotitlan, Tehuacan-Cuicatlan Biosphere Reserve, Mexico. Methods: Four groups of goats, each comprising three females of similar size and age, were fed the fruits of four endemic cactus species (Echinocactus platyacanthus f.grandis, Ferocactus flavovirens, F.robustus and F.latispinus var.spiralis). The percentage of undamaged seeds in the goat faeces was calculated at different times of collection following ingestion. Recovered seeds were tested for germination and viability, alongside seeds taken directly from the fruit. Intact and artificially cracked faecal pellets, collected from grazed natural areas, were kept in a greenhouse while seedling emergence was quantified. After 103d, all cactus seeds that remained within the faecal pellets were recovered and their germination capacity was compared to that of the seeds taken directly from fruits. Results: For the four species, between 28% and 61% of the seeds ingested were later recovered in the faecal pellets. No significant differences were found between species in the proportion of seeds retrieved during each collection time point. However, the time interval between ingestion and collection significantly influenced the number of seeds retrieved, peaking at between 16-32hr. The digestion process significantly decreased the seed germination rate. Cactus germination from cracked faecal pellets was significantly higher than from intact pellets. Both contained viable seeds of all four cactus species, but particularly E.platyacanthus f.grandis. Conclusions: Domestic goats are potential dispersers of the studied cactus species, although degradation of the faecal pellets is necessary to fully permit seedling emergence. These findings should be taken into account when designing management plans to conserve these endangered species.