Interações entre cactos e vertebrados na Caatinga, floresta tropical seca do nordeste brasileiro

Abstract

Cacti species play a major role in frugivory networks in arid and semiarid ecosystems. Several studies reinforced the role of birds, bats, and lizards as effective cacti seed dispersers, although little is known about how these interactions are distributed in a network. Our objective was to describe network structure (nestedness and modularity) of mutualistic network of cacti-seed dispersal by vertebrates at Caatinga, Rio Grande do Norte State, Brazil. We also seek to identify how much cacti species differ on the community of frugivores that feed on their fruits using the BrayCurtis dissimilarity index. For that, we monitored frugivory in six cacti species (globular Melocactus zehntneri, prickly-pear Tacinga inamoena, columnar Pilosocereus gounellei, P. chrysostele, P. pachycladus, and Cereus jamacaru) using camera-traps during eleven months, contemplating both daytime and nighttime. We found 23 vertebrate species feeding on four cacti species fruits, except on T. inamoena and P. chrysostele, and these interactions were not nested or modular, meaning that interactions within network are relatively symmetric. Our data show that cacti have a generalist strategy of attracting a wide variety of animals that provide different dispersal services, such as birds, reptiles, and mammals, all of which were recorded as primary dispersers. Despite this generalization, columnar cacti P. pachycladus and C. jamacaru, shared a similar community of frugivores, mainly birds. The columnar cactus P. gounellei was more similar to the globular M. zehntneri, and both had fruits consumed mainly by lizards (Tropidurus hispidus) and mammals, probably because they provide fruits closer to the ground. During our study, we found new interactions between lizards Salvator merianae to P. gounellei fruits and Tropidurus hispidus feeding on T. inamoena flowers, recorded during the eleven months survey with camera-traps. S. merianae consumed P. gounellei fruits in two different days, while T. hispidus were recorded eating four T. inamoena flowers in four different days in three months. Cacti offered fruits continuously throughout the year, maintaining different groups of animals that potentially play a complementary role in the dispersion of cactus seeds and, therefore, these mutualistic interactions must be considered in the conservation and restoration of semiarid environments such as Caatinga.