Factors shaping avian alien species richness in Australia vs Europe.
Aim: We aim to examine the relative importance of human activity-related and natural variables in shaping spatial patterns of alien bird species richness at the continental scale for Australia. We examine the drivers shaping establishment of alien birds in Australia in the framework of the human activity hypothesis and the biotic acceptance hypothesis (the "rich get richer" model of biotic invasion), and directly compare our results to Europe. Location: Continental Australia, Tasmania, Continental Europe, United Kingdom. Methods: We use compiled atlas data on alien bird richness in continental Australia and Tasmania together and separately, records of known alien bird introduction events compiled from various sources and a suite of biogeographic variables to evaluate drivers of alien bird richness at a 50-km resolution in Australia. We use hierarchical portioning and spatial generalized linear models to quantify the relative contribution of each environmental variable to alien bird richness. We then compare our results directly to those from a previous continental-scale study in Europe and in the UK. Results: We identify 24 established alien bird species across Australia (including nearshore islands and Tasmania) and present a detailed map of alien bird richness in Australia. We discover that in Australia, native bird species richness and land cover heterogeneity are the strongest predictors of alien bird richness at a 50-km resolution, supporting the "rich get richer" model of species invasion. Main conclusions: Our results are contrary to Europe, where the human activity hypothesis was best supported. By performing a cross-continental comparison of drivers of alien bird richness, we show that processes shaping alien establishment and spread can vary across continents with variable human impact history and should be examined on a case-by-case basis before endorsing general hypotheses.