The low level of connectivity and the high proportion of specialists in pollination networks contrast with the view that generalization rather than specialization is the norm in networks. Indeed, most plants species are visited by a diverse array of pollinators which exploit floral resources from a wide range of plant species. A main cause evoked to explain this apparent contradiction is the incomplete sampling of interactions. Indeed, most network properties are highly sensitive to sampling intensity and network size. Network studies are basically phytocentric i.e. based on the observations of pollinator visits to flowers. This plant-centered approach suffers nevertheless from inherent limitations which may hamper the comprehension of mechanisms contributing to community assembly and biodiversity patterns. First, direct observations of pollinator visits to certain taxa such as orchids are often scarce and rare interactions are very difficult to detect in field in general. Pollinator and plant communities usually are composed of few abundant species and many rare species that are poorly recorded in visit surveys.Petanidou, T. & Potts, S. G. (2006). "Mutual use of resources in Mediterranean plant–pollinator communities: How specialized are pollination webs?" In: Waser N. M., Ollerton J. (eds) Plant–pollinator interactions, from specialization to generalization, University of Chicago Press, pages 221–244. These rare species appear as specialists, whereas in fact they could be typical generalists. Because of the positive relationship between interaction frequency (f) and connectivity (s), undersampled interactions may lead to overestimating the degree of specialization in networks. Second, network analyses have mostly operated at species levels. Networks have very rarely been up scaled to the functional groups or down scaled to the individual-based networks, and most of them have been focused on one or two species only. The behavior of either individuals or colonies is commonly ignored, although it may influence the structure of the species networks. Species accounted as generalists in species networks could, therefore, entail cryptic specialized individuals or colonies. Third, flower visitors are by no means always effective pollinators as they may deposit no conspecific pollen and/or a lot of heterospecific pollen. Animal-centered approaches based on the investigation of pollen loads on visitors and plant stigmas may be more efficient at revealing plant-pollinator interactions.
