The invasive paradox: how Neltuma juliflora invasion reshapes avian diversity in a semiarid ecosystem

Abstract

Biological invasions are a dominant driver of global ecological change. It is known that invasive species can limit the survival or growth of native species, yet their full impact on biodiversity can be complex. We investigated the impact of the invasive tree Neltuma juliflora on avian communities in Brazil’s Caatinga, a seasonally dry tropical forest region. Comparing intact natural riverine forest to thickets invaded with N. juliflora, we found that N. juliflora thickets act as an ecological filter that reorganize avifauna. Contrary to expectations of simple diversity loss, invaded habitats exhibited significantly higher local (alpha) avian diversity. However, this increase was driven by a surge in generalist and open-habitat specialist species, while forest specialists declined significantly. Beta diversity analysis revealed this community shift was overwhelmingly due to species balanced variation (turnover) (92.6%), not gradient differences (nestedness). Our results demonstrate a clear invasion paradox: N. juliflora enhances local diversity providing suitable habitat for generalist species while simultaneously reducing forest specialists, posing a significant threat to the unique avifauna of the Caatinga.