Variation in post-dispersal predation of cactus seeds under nurse plant canopies in three plant associations of a semiarid scrubland in central Mexico

This study compares the post-dispersal predation of seeds from the cacti Myrtillocactus geometrizans and Opuntia pilifera by diurnal vertebrates, nocturnal vertebrates, and ants under nurse plants in three plant associations found in the semiarid scrubland of Tehuacán Valley (Mexico). Experiments on seed removal showed that, regardless of cactus species and plant association, ants were the main seed predators. Predation of M. geometrizans seeds varied depending on plant association and predator type, but it could not be associated with the abundance of granivore guilds; seed predation was more prominent in scrublands dominated by Beaucarnea gracilis. For O. pilifera, seed predation by ants was more intense in scrublands dominated by Neobuxbaumia tetetzo, but there was a significant interaction between plant association and predator type. These results support the existence of spatial variability in interactions between seeds and granivores above the microhabitat scale, which—to varying degrees of intensity—influences the distribution of seeds dispersed by frugivorous animals. This among-plant association variability in seed–granivore interactions, in addition to the within-plant association variability (e.g. nurse canopy vs. open area), should be taken into account when studying the causes of differential recruitment of plant species in arid environments.