Plant-animal interactions are key processes in the maintenance of ecosystem functioning. Most tropical fleshy fruited plant species rely on animals to disperse their seeds, which in turn rely on those fruits as a food resource. Thus seed-dispersal directly influences vegetation structure and community dynamics in tropical forests. Seed dispersal efficiency is mainly affected by species functional traits, phenology, diet, body mass, co-occurrence of interacting partners, and suitable habitats. Many anthropogenic activities can disrupt seed-dispersal interactions, such as defaunation and introduction of alien species. The loss of animals with large body size, for example, can lead to a cascade effect on lower trophic levels with consequences to species, interactions, and ecosystem functioning. Likewise, alien species are known to outcompete native species and change ecosystem processes although recent studies are discussing aliens' positive effects on replacing functionally extinct species and re-establishing lost interactions. Ecological networks are an important tool to describe patterns and processes of species interactions and have been applied to understand how communities respond to anthropogenic disturbance and rapid evolutionary changes. Here we will apply the theory of ecological networks to understand how defaunation and alien species affect seed-dispersal systems in the Atlantic Rainforest. We will evaluate how the degree of defaunation and the intensity of invasion affect the structure of seed-dispersal networks at different landscape scales. Furthermore, we will analyse the influence of species functional traits and phylogenetic diversity on network structure and robustness. We aim to identify keystone species and interactions, as well as structural patterns fundamental to seed-dispersal network stability at different landscape scales and under different degrees of defaunation and invasion. Based on the results from the network structural analyses, our final goal is to deliver conservation strategies, working together with practitioners and reserve managers, to ensure an efficient seed-dispersal process at different scales of the Atlantic Rainforest biome, either by maintaining or restoring vanished interactions and functions.
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