Cactus height increases the modularity of a plant-frugivore network in the Caatinga dry forest

Cacti fruits are key resources to many frugivorous animals in Neotropical arid and semiarid regions. However, most studies have focused on a particular animal group or cacti species, but few have explored the overall interactions of such species at the community level. Here we monitored frugivory on five cacti species using camera traps that sampled diurnal and nocturnal interactions. We investigated the structure of interactions with bird, mammal, and reptile frugivores in the Brazilian Caatinga dry forest. We hypothesized that the height of cacti limit interactions with different types of frugivores, which would result in highly structured and modular interaction networks. In 2929 camera-days, we recorded 23 vertebrate species feeding on cacti fruits, including seven new records, all determined to be primary seed dispersers. As predicted, the cacti-frugivore network was modular and non-nested, with the two shortest cacti species grouped in a module dominated by interactions with reptiles and non-flying mammals. The tallest cacti species were dominated by frugivory interactions with birds and had comparatively less interaction diversity than shorter cacti species. Our results support the contention that cacti are keystone species in semiarid ecosystems where they produce small-seeded fleshy fruits year-round.