Invasão do Cerrado pela Braquiária (Urochloa decumbens): impacto na predação de sementes e potencial de disseminação por formigas

Abstract

Biological invasions are a threat to native biodiversity. African grasses (such as brachiaria, Urochloa decumbens) are present in almost all Cerrado fragments, and is one one of the main challenges in the conservation of Cerrado. There is no information about the impacts of this invasive on seed predation in the Cerrado. Rodents, ants and birds are important agents of seed predation, and changes in vegetation cover can alter their abundance and foraging. It is known that U. decumbens accumulates hig biomass in the invaded areas, providing milder microclimate conditions, and it may serve as a shelter for seed removal agents, which could change seed predation rates. The spread of U. decumbens occurs by wind, vegetative propagation and the transit of animals and cars. It is not known if ants may disperse U. decumbens, and in this way, they would enhance the invasion. Therefore, the objectives of this study were: to understand if the presence of U. decumbens changes native seed predation and U. decumbens seed, and if ants are helping to spread the invasive species. The experiments were done in fragments of Cerrado in Itu, Itirapina and Águas de Santa Barbara municipalities, during the summer. To test whether the presence of U. decumbens would alter seed predation, we performed exclusion experiments. To check if ants were acting as dispersers of the invasive grass, we performed tetrazolium tests on the seeds of U. decumbens sampled from ant nests. We found that invaded sites have less seed predation, which suggests that seed predation is probably not affecting natural regeneration in places invaded by U. decumbens. We verified that ants are acting as dispersers of the invader, transporting viable seeds to their nests, where there is probably higher chance for germination and seedling development in relation to the surroundings due to the accumulation of nutrients, and patrolling activity of ants in their nests.. Therefore, our results suggest an increase in complexity about what we know about the dynamics of U. decumbens invasions and suggests important information for the management and control of the invasive grass.