, 
Understanding the persistence of specialists and generalists within
ecological communities is a topical research question, with far-reaching
consequences for the maintenance of functional diversity. Although theoretical
studies indicate that restricted conditions may be necessary to achieve
coexistence between specialists and generalists, analyses of larger empirical
(and species-rich) communities reveal the pervasivness of coexistence. In this
paper, we analyze 175 ecological bipartite networks of three interaction types
(animal hosts-parasite, plant-herbivore and plant-pollinator), and measure
the extent to which these communities are composed of species with different
levels of specificity in their biotic interactions. We find
a continuum from specialism to generalism. Furthermore, we demonstrate that
diversity tends to be greatest in networks with intermediate connectance,
and argue this is because of physical constraints in the filling of networks.
Keywords: bipartite networks; specificity; nestedness; modularity;
food webs; parasites; pollinators; herbivores