Maintenance of Pollinator Function in Restored Vernal Pools: Gnats Filling the Role of Solitary Bees

Abstract

The role of plant-pollinator interactions in influencing the success of ecological restoration projects is important and often overlooked. In our study, we examined floral visitation in an endangered vernal pool plant species, Contra Costa Goldfields (Lasthenia conjugens; Asteraceae). We observed Goldfields abundance and floral visitation in the early and late stages of an ecological vernal pool restoration project located in the Central Valley of California. After an initially high abundance at our study site in the early stages of restoration, we noted a sharp decline of this endangered species ten years later. Our floral visitor observations demonstrated that the abundance of gnats (Sciaridae) was high in the restored pools across the ten years, but was very low to nonexistent in the nearby naturally occurring pools. Solitary bee abundance was the inverse of that observed for gnats, with a very low instance of solitary bee pollinators in the restored pools, yet a higher abundance in the naturally occurring pools. With this difference in floral visitors between pool types, we found significantly more mature potentially viable seeds in the restored pools, but a general overall decline over the three observation years. The higher number of mature, potentially viable seeds in the restored pools leads us to believe that the gnats are filling the role of the solitary bees and have maintained this function over the duration of the ten-year observation period. We conclude that gnats may be acting as surrogate pollinators for Goldfields in restored pools.