Invasive Grass and Honeybees Alter Plant-pollinator Network Structure in the Brazilian Caatinga

Abstract Invasive species are one of the most important threats to ecosystems. While invasive plants can interact directly with native pollinators, wind-pollinated grasses can also indirectly affect plant-pollinator networks by changing plant and animal community composition and, ultimately, decreasing ecosystem functioning. Here, we investigated the effect of invasive grass on pollinator richness, visitation number, and the structure of plant-pollinator networks. Further, we tested the impact of the non-native honeybee on pollinator richness, visitation number, and network structure in the Caatinga. Invasive grass negatively affected native pollinators and reduced visitation number on native plants. The dominance of the invasive grass increase plant competition, which led to an increased of niche overlap among native pollinators but did not affect the number of visits by non-native honeybees. However, increase in visitation number by honeybees reduced native pollinator richness by 60%. Our findings suggest a negative potentialized effect of invasive grass and non-native honeybee on the native plant-pollinator dynamics. The invasive grasses reduce the number of pollinators visits indirectly through changes in plant community composition that may reduce the attractiveness of patches dominated by invasive grasses. Honeybees were not affected by the invasive grass but reduced the richness of native pollinator species and the number of visits they perform, suggesting an important effect of biological invasion on ecosystem resilience. Our research helps to understand how invasive species, directly and indirectly, impact the plant-pollinator interactions and his influence on ecosystem functioning in abandoned lands in dry semiarid ecosystems.