COS 42-1 - Competition-driven pollinator specialization in longleaf pine savannas

Abstract: Species trophic specialization, i.e., the tendency of species to interact with few partners, is central to ecological networks and ecosystem functioning. Trophic specialization is intrinsically related with functional redundancy, complementary, and efficiency, driving ecosystem functioning. However, global change is altering trophic specialization across ecosystems, selecting for more generalized communities. Species trophic specialization is not static, and varies depending on the ecological context. Despite this, little is known about the main drivers of species trophic specialization. Some of the main factors that drive specialization include intraguild competition and resource availability. Intraguild competition limits the resource availability, leading to niche partitioning, and greater specialization whereas resource availability increases the partner choice. Here, we studied the effects of intraguild competition and resource availability on trophic specialization using plant-pollinator communities across 24 sites in North and Central Florida during the whole flowering season of 2019. In particular, we studied taxonomic, phylogenetic, and functional specialization of pollinators (i.e., the species, lineages, and functional traits of the plants that pollinators visit). We found that intraguild competition exerts the largest effect on trophic specialization, leading to the higher generalization of pollinator assemblages. Intraguild competition has a high cost, reducing the available floral rewards, and prompting pollinators to visit resources that they would not normally use. This relationship suggests that pollinators have large fundamental niches and are resilient to global change. However, the decrease of species diversity with global change may still decrease pollinator local generalization and alter plant reproduction. The effect of plant resources was less marked, but overall increased pollinator trophic specialization. The effect of plant resources on trophic specialization suggests that pollinators interact with a smaller proportion of the available plants in resource-rich communities.