Variation in nectar robbing over time, space, and species

Spatiotemporal variation in the interactions among plants and animals is widespread; yet our conceptual and empirical understanding of this variation is limited to a few types of visitors, mainly herbivores, pollinators, seed predators, and seed dispersers. Despite the ubiquity of nectar robbing and the strength of its effects on plant fitness, we know relatively little about the magnitude and, intensity of spatial and temporal variation in interactions among plants and nectar robbers. The purpose of the present study was to quantify spatial and temporal variation in the interactions between a nectar-robbing bumblebee and its host plants. In the Rocky Mountains of Colorado, USA, over 7 years, and multiple locations, we measured levels of nectar robbing by the bumblebee Bombus occidentalis and its interactions with four different host plants, Delphinium nuttallianum (Ranunculaceae), Ipomopsis aggregata (Polemoniaceae), Corydalis caseana (Fumariaceae), and Linaria vulgaris (Scrophulariaceae). Significant variation was found in the robbing rates experienced by different species. Within species, there was variation in robbing rates on an annual basis, on a seasonal basis, among different sites, and within sites. This variation may have important consequences with respect to the population dynamics of host plants as well as selection on floral and flowering traits.