Aim Niche conservatism, or the extent to which niches are conserved across space and time, is of special concern for the study of non‐native species as it underlies predictions of invasion risk. Based on the occurrence of 28 non‐native birds in Europe, we assess to what extent Grinnellian realized niches are conserved during invasion, formulate hypotheses to explain the variation in observed niche changes and test how well species distribution models can predict non‐native bird occurrence in Europe. Location Europe. Methods To quantify niche changes, a recent method that applies kernel smoothers to densities of species occurrence in a gridded environmental space was used. This corrects for differences in the availability of environments between study areas and allows discrimination between ‘niche expansion’ into environments new to the species and ‘niche unfilling’, whereby the species only partially fills its niche in the invaded range. Predictions of non‐native bird distribution in Europe were generated using several distribution modelling techniques. Results Niche overlap between native and non‐native bird populations is low, but niche changes are smaller for species having a higher propagule pressure and that were introduced longer ago. Non‐native birds in Europe occupy a subset of the environments they inhabit in their native ranges. Niche expansion into novel environments is rare for most species, allowing species distribution models to accurately predict invasion risk. Main conclusions Because of the recent nature of most bird introductions, species occupy only part of the suitable environments available in the invaded range. This signals that apart from purely ecological factors, patterns of niche conservatism may also be contingent on population‐specific historical factors. These results also suggest that many claims of niche differences may be due to a partial filling of the native niche in the invaded range and thus do not represent true niche changes.

Urbanisation represents one of the most radical forms of terrestrial land use change and has been shown to lead to alterations in ecosystem functioning and community dynamics and changes in individual phenotypic traits. While the recent surge in microbiome studies has brought about a paradigm shift by which individuals cannot truly be considered independently of the bacterial communities they host, the role of gut microbiota in organismal response to human-induced environmental change is still scarcely studied. Here, we applied a metabarcoding approach to examine the impact of urbanisation on the gut microbiota of Passer domesticus. We found urbanisation to be associated to lower microbiota species diversity, modifications in taxonomic composition and community structure, and changes in functional composition. The strength of these relationships, however, depended on the spatial scale and season at which they were considered. Such spatio-temporal effect suggests that urbanisation may dampen the natural seasonal variation of the gut microbiota observed in more pristine habitats, potentially influencing the fitness of urban organisms. Our results hence shed light on a hitherto little considered perspective, i.e. that the negative effects of urbanisation on city-dwelling organisms may extend to their microbiomes, causing potential dysbioses.

Aim Invasive alien species are a growing threat to biodiversity, and identifying the mechanisms that enable these species to establish viable populations in their new environment is paramount for management of the problems they pose. Using an unusually large number of both failed and successful documented introductions of parakeets (Aves: Psittacidae) in Europe, we test two of the major hypotheses on the establishment success of invading species, namely the climatematching and the human-activity hypothesis.Location European human population centres where ring-necked parakeet (Psittacula krameri) and/or monk parakeet (Myiopsitta monachus) introductions have occurred.Methods Data on ring-necked and monk parakeet introductions in Europe were gathered from various sources, including published books and articles, but also from unpublished reports and local grey literature. Information was verified with experts from the region under consideration. In order to test the climatematching hypothesis, we verified whether the climatic factors that determine the parakeets' native ranges also explain establishment success in Europe. Parakeet occurrence data from the native ranges were analysed using the presence-only modelling method Maxent, and correlations between parakeet establishment and climatic and anthropogenic variables in Europe were assessed using both stepwise logistic regression and the information-theoretic model selection approach. ResultsThe establishment success of ring-necked and monk parakeets was found to be positively associated with human population density, and, both in the native and in the introduced regions, parakeet occurrence was negatively correlated with the number of frost days. Thus, parakeets are more likely to establish in warmer and human-dominated areas.Main conclusions The large number of independent parakeet introductions in Europe allows us to test the often-used climate-matching and human-activity hypotheses at the species level. We show that both hypotheses offer insight into the invasion process of monk and ring-necked parakeets. Our results suggest that, in the future, parakeet establishment probability may increase even further because global warming is likely to cause a decrease in the number of frost days and because urbanization and human populations are still increasing.

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European Union’s ban on trade in wild-caught birds both reduces and redistributes bird invasion risk globally.