Bee and Flowering Plant Communities in a Riparian Corridor of the Lower Rio Grande River (Texas, USA)

The Rio Grande in Texas is the geopolitical boundary between the United States and Mexico. Considered one of the world's most at-risk rivers, it has been impacted by intensified management by both countries sharing its watershed. Invasion by Arundo donax (Linnaeus) (Poales: Poaceae), giant reed, has been extensive in the riparian corridor, with potential impacts on native wildlife. A need exists to better understand the ecological communities in these habitats to support strategies for enhancing resources for pollinators. We sampled bee and flowering plant communities monthly over 2 yr along a 3.22 km stretch of the lower Rio Grande in Webb County, TX. Bee and plant richness and abundance were bimodal with peaks in March-April and September in both riparian and upland habitats. The bee community was similar across habitats and sampling dates and dominated by a few common species. Anthophora occidentalis (Cresson) (Hymenoptera: Apidae) and Lasioglossum sp. L (Curtis) (Hymenoptera: Apidae) were indicator species of the riparian habitat, and Halictus ligatus (Say) (Hymenoptera: Halictidae) was an indicator species of the upland habitat. Three plant species were indicator species in riparian habitats, spiny pricklepoppy (Argemone sanguinea Greene) (Papaverales: Papaveraceae), spotted beebalm (Monarda punctata Linnaeus) (Lamiales: Lamiaceae), and Pennsylvania cudweed (Gamochaeta pensylvanica Willdenow) (Asterales: Asteraceae). Analysis showed a positive relationship between bee richness and abundance with flowering plant diversity, increasing bee richness within an optimal temperature range 25-30°C, and higher bee abundance with increased average monthly precipitation. This geographically extensive riparian corridor could be managed using ecological restoration to enhance resources for pollinators.