The timing of life history events is being altered by climate change and other anthropogenic environmental changes, with potential functional consequences. Such changes may be particularly important in mutualisms, such as plant-pollinator interactions, where timing mismatches can impact fitness in both plants and pollinators. Numerous studies have examined how changes in flowering phenology could impact the seed set of individual species, yet it is the changes to relative fitness among species that shape coexistence and community composition. To understand how phenological change can affect plant community seed set, we conducted a large-scale snowmelt acceleration experiment to advance flowering phenology in eight montane meadow communities across two valleys in the Rocky Mountains of Colorado, USA. Each snowmelt acceleration plot (10 m x 14 m) was paired with an adjacent control plot without snowmelt manipulation (16 plots total). In six plots and their adjacent controls, we measured how phenological change altered the fecundity of eight co-occurring plant species, evaluating pollen limitation in five species using hand pollination treatments. Although accelerating flowering phenology resulted in lower overall fecundity and greater pollen limitation in the examined assemblage of focal species, these changes occurred in different directions depending on the species. Species-dependent responses were also reflected in a significant change in the relative proportions of seeds produced by different plants. Our results suggest potential impacts on future plant community composition resulting from early snowmelt, and underscore the importance of studying the impacts of phenological change at a community level.

Pollinator foraging behavior determines floral visitation rates, an important proxy to the strength of mutual- istic interactions. Although there is evidence that pollinators modify their behavior in the presence of other foragers, there are equivocal findings regarding whether or not pollinators interfere with one another. We employ a functional-response framework to analyse experimental data of times between floral visits made by a focal pollinator and to estimate pollinator interference by conspecifics and three other species. Additionally we develop and compare models that allow different levels of resource availability and the sub-lethal exposure to a neonicotinoid pesticide to modify how pollinators forage alone and with co-foragers. We found that all co-foragers interfere with a focal pollinator under at least one set of abiotic conditions; for most species, interference was strongest at higher levels of resource availability and with pesticide exposure. Overall our results highlight that density-dependent responses are often context dependent themselves.