Technical Abstract: Pollination of flowers by insects is a flagship interaction for studying mutualism and coevolution. However, until recently most research has focused on single plant species with one or a few pollinator species. Vigorous discussion of the degree of specialization in pollination interactions, combined with advances in the analysis of complex networks, have now revitalized the study of entire plant-pollinator communities. Noticeably absent to date are attempts to quantify temporal variation in the structure and topology of plant-pollinator networks, and to determine whether the status of species as specialists or generalists is stable. Here we show that network topology varied through time in a montane meadow community from southern California, in that pollinator species did not form the same links with plant species across years. Furthermore, composition of the generalized core group of species in the network varied among summers, as did the identify of those species involved in the specialized relationships that comprise compartments within the network. These differences are likely attributable to severe drought conditions experienced in the second summer of the 3 year study. Interestingly, the pollinator community remained similarly highly nested in all three summers, even though species were packed into the nested matrix differently from year to year. These results suggest the plant-pollinator networks vary in detail through time, while retaining some basic topological properties. This dynamic aspect of community-scale interactions has implications for both ecological and evolutionary inferences about pollination mutualisms.