Assessing and predicting the spread of non-native raccoons in Germany using hunting bag data and dispersal weighted models

As the second largest cause of biodiversity loss worldwide, there is an urgent need to study the dynamics of biological invasions and identify factors limiting the distribution of invasive alien species. In the present study we analyze national-scale hunting bag data from Germany to predict the dispersal of raccoons in the largest non-native population of the species. Our focus is (1) to document changes in the distribution and abundance of raccoons, (2) to identify the species-environment relationship and predict which areas will be suitable for future colonization and (3) to apply a dispersal model to predict how fast the raccoon will spread to these areas. The increase from about 9,000 harvested raccoons in 2000/01 to about 71,000 in 2011/12 reflects the extensive amount of suitable habitat for this omnivorous species in Central Europe. The best model for explaining range expansion in Germany identified coverage of agriculture and fragmentation and coverage of forests as the most important explanatory variables. The range of raccoons (area with harvest index > 0.1 per 100 ha) increased from 26,515 km2 in 2001 to 111,630 km2 in 2011, and is predicted to expand to 252,940 km2 by 2061, 71 % of the area of Germany. This vast area encompasses strategically important areas for conservation biology, such as wetlands with endangered native terrapins. The combination of merging of separated introduced populations and accelerating population growth highlights the potential for future impacts of raccoons on native communities, ecosystems and economic life in Germany and Central Europe.