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 2,929 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.