Background/Question/Methods Defaunation has been occurring in many areas around the Globe, especially in tropical forests, with profound effects on species diversity and composition of forest plants. We simulated the absence of different animal species on a seed dispersal network to address the changes that defaunation can causes on its pattern. The seed dispersal network was sampled in the Pantanal, a wetland that stretches through Central-West Brazil, Bolivia and into Paraguay. We sampled 275 interactions between 48 fleshy-fruited species and 47 species of seed dispersers. The six different scenarios of defaunation were simulated through the removal of medium and large-bodied animal species from the original network, in which the order of removal was based on the body mass of the species.

Results/Conclusions The pattern of the network was nested in all defaunation scenarios, although the value of nestedness considerably decreased as the network became more defaunated. The network was also considered modular in all scenarios, but the modularity index increased as the network became more defaunated. With defaunation, several plant species ended up depending on very few seed dispersers. Furthermore, our simulation showed that, at the most defaunated scenario, 33% of the plant species lost all their seed dispersers. When we analyzed scenarios based on the removal of random species (in which the order of removal was not based on the body mass of the seed disperser), there were no significant differences in the values of both nestedness and modularity among the different scenarios. In addition, not a single plant species lost all seed dispersers at the most defaunated scenario. These results show that medium- and large-bodied seed dispersers can differentially affect the pattern of the network, when compared to “random” species. A less nested and more modular network is less robust when facing disturbances, as well as less connected. Based on both quantitative and qualitative data from the original network, we also documented the effects of the loss of medium and large body animals on the number of plant species dispersed, as well as on the size of the dispersed seeds. The number of plant species dispersed decreased as the body size of seed dispersers decreased, as well as the average diameter of all dispersed seeds found in scats or ingested during the focal observations.