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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. Electronic supplementary material is available if you access this article at http://dx.doi.org/10.1007/s00442-002-1060-z. On that page (frame on the left side), a link takes you directly to the supplementary materials.

Many insects and other animals that visit flowers are not mutualistic pollinators, but rather "behavioral robbers" which pierce flowers to extract nectar, and "thieves" which enter flowers in the normal way but provide little or no pollination service. Although the study of floral larceny has grown rapidly in the last two decades, the importance of larceny for individual fitness and for population- and community-level phenomena is only now becoming apparent. Here we synthesize the current understanding of floral larceny by reviewing and re-analyzing existing published data, by presenting new data of our own, and by suggesting avenues of further research. First, we perform a meta-analysis on existing studies, which shows that larceny has an overall detrimental effect on female reproductive success of plants, and that effect size depends on the types of robbers, thieves, and pollinators that interact as well as on the reproductive biology of the plant. This quantitative analysis improves upon a recently published qualitative analysis of larceny and plant fitness. Next, we discuss the possibility that larcenists and pollinators can select in different directions on floral traits, possibly contributing to the standing variation in floral phenotypes that is observed within natural populations. Larceny has the potential to affect plant population dynamics, so long as offspring recruitment and survival depend on seed production, a point we illustrate with data from the montane herb Ipomopsis aggregata. Our studies of this species also show how larcenists may influence community-level dynamics, by linking plant species that they rob or by influencing other plant species through altered behavior of shared pollinators. Population- and community-level effects of larceny, and their possible roles in stabilizing pollination food webs, provide rich prospects for future research.