Florivory on an alien tree as a potential case of biotic resistance provided by urban parrots

Alien plants grown in urban areas can spread through natural and anthropogenic ecosystems, adversely impacting native biota. Propagule pressure (i.e., seed, individual, and introduction number) increases the spreading probability, but native herbivorous predators can limit it via biotic resistance. Parrots are primary consumers, and although they interact antagonistically with alien plants, their role in biotic resistance seems overlooked. Here, we highlight the potential role of urban parrots in biotic resistance based on florivory activity in Gliricidia sepium (Fabaceae), an alien tree with invasive traits. We performed focal observations on four G. sepium trees planted in an urbanized area in Brazil to assess parrot florivory magnitude. As a complement, we performed road transects to record food plants and determine whether parrots prefer G. sepium over native plants, a significant fact from the perspective of biotic resistance. Parrots prey on 33% of G. sepium flower crops in 16 h, presumably resulting in seed loss for recruitment – ​​florivory occurs before fruit and seed formation and may characterize a type of predispersal seed predation. Three parrot species preferred G. sepium flowers to some native food plant species. Our investigation suggests that parrots potentially provide biotic resistance in urbanized areas by exerting high predation pressure on the reproductive structures of alien plants. Maintaining native urban parrots can be a conservation tool to resist invasion by alien plant species. Parrot food plants, mainly native ones, should be urban greening options to enhance this ecological function.