Ungulates alter floral community composition and increase competition with native bees

The breadth of management goals in large and complex landscapes has grown to encompass biotic communities with varied life histories and across trophic levels, like ungulates and bees. However, ungulates may trample and have dietary preferences for forbs, which reduces the floral resources available to bees. We investigated how management of wild and domestic ungulates influence bee communities in a riparian forest in northeastern Oregon, USA, by observing the response of bees and blooms to grazing by cattle, wild ungulates (deer and elk), and a combination of cattle and wild ungulates across three growing seasons. Using a series of motion activated game cameras, cumulative herbivore pressure was monitored for each ungulate assemblage throughout the growing season. While there was no effect of ungulate assemblage type on bloom abundance or richness, there was a negative association between cumulative herbivore pressure and bloom and bee abundance. Additionally, grazing by cattle shifted the bloom composition later in the growing season, by favoring weedy annual flowers. Furthermore, using information on elk dietary preferences and bee-flower associations, we found that elk-preferred forbs declined in abundance with wild ungulate grazing pressure but received higher bee visitor richness than non-elk-preferred forb species, indicating that the dietary preferences of elk could reduce the abundance of attractive plants for bees. The co-occurrence of wild and domestic ungulates likely increases the number of individuals that reduce floral resources for bees, and also increases competition for floral resources through dietary overlap.