Precipitation and the robustness of a plant and flower-visiting insect network in a xeric ecosystem

Complex networks of species interactions are integral to the stability of ecological communities. The responses of these networks to extreme environmental fluctuations are key to understanding the evolution of these networks and their roles in stabilizing ecological communities. From 2008 to 2009 we observed the effects of extreme differences in annual precipitation on a network of plants and flower-visiting insects in a xeric grassland. Significant decreases in plant and insect diversity in the dry year were mirrored by decreases in the number of network nodes and links. However, the relative density of network connections increased in the dry year and other important topological features, such as nestedness and modularity, were largely unchanged. The resilience of the network to node (plants or insect species) loss was high in both years. Though bees tend to dominate pollination communities in drier climes, we did not observe a shift in the relative richness of bee species in the dry year. Our results indicate that well-linked, drought-resistant plants are important to community resilience during ecologically challenging periods and that networks of plants and flowering-visiting insects may be robust to extreme climatic change, at least over short periods, as long as those critical, resilient hubs are protected.