An overlooked invader? Ecological niche, invasion success and range dynamics of the Alexandrine parakeet in the invaded range

Parrots and parakeets (Aves, Psittaciformes) are prominent among avian invaders, as more than 16 % of living species are currently breeding with at least one population outside their native range. Most studies have been carried out on ring-necked and monk parakeets, as they are the most successful invasive parrots globally. Recently, however, reports of invasive Alexandrine parakeet Psittacula eupatria have increased. Here, we summarize the current knowledge on the current occurrence of Alexandrine parakeets outside the natural range and assess the degree of niche conservatism during the invasion process. Our results show that Alexandrine parakeets have established invasive populations predominantly in Europe, parts of the Middle east and Far Eastern countries such as Japan and Singapore. During the ongoing invasion of Europe, the Alexandrine parakeet considerably expanded its niche into colder climates with respect to those occupied in the native range. Our results offer some support to the hypothesis that interspecific facilitation with previously established ring-necked parakeets Psittacula krameri may contribute to niche expansion and invasion success of congeneric Alexandrine parakeets. Species Distribution Models including both native and invaded range occurrence data predict a high invasion risk across multiple parts of the globe where the species is currently not yet present, thus indicating a high potential for the species for further invasion success and range expansion.