Authors: Tedeschi, Lisa; Essl, Franz;Capinha, César;Rondinini , Carlo ;

Biological invasions are amongst the main drivers of biodiversity change and decline; despite increasing efforts, the spread of invasive species continues unabated. We present an analysis on propagule pressure (introduction effort) for 71 alien mammal species in Europe, whereby we predicted each species' range size based on points of introduction, dispersal distance, generation length, and residence time. We then calculated the filling ratio for each species (observed/predicted range size) and used it as a response variable in a generalized mixed model, to quantify the effect of a wide array of event-, species-, and location-level predictors on filling ratio. Predictors included, among others, propagule pressure, points of introduction, human footprint index, and climate matching.
We found that many alien mammals’ predicted ranges were significantly broader than their observed ranges, suggesting that environmental or biotic factors may limit species’ spread. Nonetheless, we found that propagule pressure and pathway of introduction played a major role in determining alien mammals’ range sizes. Both factors ultimately depend on human behaviour rather than species or environmental characteristics. Our results indicate that alien mammals’ distribution in Europe is largely shaped by anthropogenic activities, confirming that preventing future introductions is key to limit further alien species’ spread.