Bee Biodiversity and Plant-Pollinator Networks in the South Llano River Basin of Texas

Pollinators are essential for biodiversity and ecosystem stability, yet their biodiversity is declining due to habitat loss, climate change, and other anthropogenic stressors. This study examines bee community composition and plant-pollinator network structures across riparian and upland habitats in the South Llano River Basin (Kimble County, Texas). Over six months of sampling, bee abundance, diversity, and functional group composition were analyzed in relation to habitat types and the composition of local plant communities. Results show that the managed upland habitat supported the highest bee abundance, while unmanaged upland habitats exhibited the highest diversity and species evenness. Riparian zones had lower species richness than upland unmanaged but higher species richness than upland managed habitat. Functional group analyses revealed that long-tongued and social bees were more abundant in riparian and upland managed habitats, whereas short-tongued and solitary bees were more evenly distributed across all habitats. Plant-pollinator network analysis demonstrated that upland habitats fostered more specialized and modular pollination networks, while riparian areas supported more generalized interactions. Network resilience analysis showed that upland habitats were the most stable, while riparian networks were more vulnerable to species loss. Key abundant pollinators, such as Bombus sonorus and Apis mellifera, were central to maintaining network connectivity. Bee communities and functional groups were observed to vary significantly between habitats, but the drivers are yet unknown. These findings highlight the importance of different habitats in sustaining diverse and resilient pollinator communities. While riparian corridors act as species rich hotspots, upland habitats contribute to network stability through more specialized interactions, and managed upland habitats provided abundant floral resources but showed reduced species evenness. This was likely the result of this system maintaining high floral abundances across sampling dates due to supplemental irrigation and cultivation. Conservation efforts for native bees should prioritize protecting and restoring diverse floral resources across different habitats, and protecting and restoring habitats that support both generalist and specialist pollinators to enhance long-term pollination networks.