Ecological networks, the sets of links that connect species to one another through their ecological functions, constitute the foundation of biodiversity, and the understanding of their properties and dynamics represents one of the most important challenges for our society, faced with the global change of ecosystems. Most studies of ecological networks use species as basic interactors, assuming that all individuals of a species have the same ecological role. However, there is intraspecific variability in individual traits or properties related to the establishment of interactions among species. In mutualistic networks connecting plants with their pollinators and seed dispersers, an individual's preference to feed on --and therefore disperse pollen or seeds of-- one or another plant species may depend on individual nutritional needs, which in turn depend on the health status of the individual. We are exploring these types of extrinsic influences on network properties using two study systems: the network that links hummingbirds with the plants they pollinate, and the one that links understory birds with the plants they help to disperse. We will analyze the effect of avian malaria and virus infections on the structure and properties of these networks. We hypothesize that diseased birds will prefer distinctive sets of plant species, particularly those that contain nutrients important for their maintenance in the face of infection.If network properties change predictably depending on which individuals (infected or healthy) are used to calculate network parameters, the architecture of mutualistic networks will depend on pathogen prevalence, an overlooked mechanism to explain disease impacts on ecosystems with important implications for ecology and conservation biology.