Plantas introduzidas e seu papel na diversidade de plantas nativas e seus visitantes florais: um caso em uma área de restauração

Abstract

Invasive species are a common component of human-modified landscapes, affecting biological communities and species interactions globally and potentially interfering with the structure and dynamics of plant-pollinator networks. While invasive plants can interact directly with native pollinators, wind-pollinated grasses can also indirectly affect plantpollinator interactions by inducing shifts in the animal community composition and structure and decreasing insect pollinators visitation rates. However, the indirect effects of invasive species on pollinator insect richness and the plant-pollinator network structure have been poorly explored, limiting our ability to predict the effects of biological invasion on ecosystem resilience. We measured the effect of the Megathyrsus maximus cover, an invasive grass species, in the plant-pollinator network structure into an abandoned pasture left to regeneration in a dry tropical ecosystem (the Brazilian Caatinga). We aimed to investigate the effect of this invasive grass on the: (i) diversity of pollinators; ii) frequency of floral visitation; iii) structure of plant-pollinator ecological network; and (iv) the combined effects of the invasive grass and an alien honeybee (Apis mellifera) on insect community and plant-pollinator network structure. We found that the invasive grass cover had a negative effect on the native insect richness and reduced visitation frequency of native pollinators. Dominance of the invasive grass on plant communities increased niche overlap among pollinators but did not affect visitation frequency of honeybees. However, the increase in visitation frequency of A. mellifera reduced by 60% the richness of native insect pollinators. Our findings suggest a combined effect of the biological invasion. First, the invasive grass reduces the native plant diversity and indirectly, increases the frequency of honeybees visitation that may in turn reduce diversity and frequency of native insect pollinators. These results reinforce that invasion of plants may trigger cascade effects with multi-trophic consequences in ecological networks that may affect the resilience and regeneration of invaded ecosystems. Our research helps to tease apart how indirect effects of alien plant and insect species in a plant-pollinator system could boost biotic homogenization and depletion of floral resource depletion in naturally regenerating areas.