Bird species’ centrality in seed-dispersal networks varies within climatic niches

Understanding how the functional role of species within seed-dispersal networks varies across geographical and climatic gradients can reveal the mechanisms driving network organization. Using data for 157 bird species from all continents, we evaluated the variation of species’ centrality within local networks across species’ climatic niches (occupied climatic conditions) and in response to proxies of competition (number of co-occurring bird species) and resource availability (number of co-occurring plant species). We found that species’ centrality increases towards the climatic niche centroid for most bird species. The effect of competition on species’ centrality was usually opposite to that of resources (i.e., when one was positive, the other was negative), regardless of the network’s position within the climatic niche space. Taken together, our results show that species’ centrality within seed-dispersal networks is influenced by the climatic suitability of network location, supporting the niche centrality hypothesis, whereas competition and resource availability exert opposing effects.