Range Expansion of Ambrosia artemisiifolia in Europe Is Promoted by Climate Change

Ambrosia artemisiifolia L., native to North America, is a problematic invasive species, because of its highly allergenic pollen. The species is expected to expand its range due to climate change. By means of ecological niche modelling (ENM), we predict habitat suitability for A. artemisiifolia in Europe under current and future climatic conditions. Overall, we compared the performance and results of 16 algorithms commonly applied in ENM. As occurrence records of invasive species may be dominated by sampling bias, we also used data from the native range. To assess the quality of the modelling approaches we assembled a new map of current occurrences of A. artemisiifolia in Europe. Our results show that ENM yields a good estimation of the potential range of A. artemisiifolia in Europe only when using the North American data. A strong sampling bias in the European Global Biodiversity Information Facility (GBIF) data for A. artemisiifolia causes unrealistic results. Using the North American data reflects the realized European distribution very well. All models predict an enlargement and a northwards shift of potential range in Central and Northern Europe during the next decades. Climate warming will lead to an increase and northwards shift of A. artemisiifolia in Europe. 1. Introduction Ambrosia artemisiifolia L. (common ragweed), native to North America, is considered as one of the most problematic invasive species in Europe (e.g., [1]). The species produces highly allergenic pollen in huge amounts (e.g., [2]). Up to 12% of the human population suffers from allergy (rhinitis and asthma) to Ambrosia pollen [3]. The medical costs of people with allergies are enormous (e.g., [3]) and will increase in case of a further spread of A. artemisiifolia in Europe. The invasion of A. artemisiifolia into Europe proceeded in two stages: (1) A. artemisiifolia was inadvertently introduced into Europe in the 19th century and has become a widespread alien species in South-eastern Europe [4]. (2) In the last decade many expanding populations of A. artemisiifolia in Central and Northern Europe have been evidenced [5]. Climate change and invasive species are regarded as major threats to biodiversity (e.g., [6, 7]). Invasive species may induce economic problems, particularly in agriculture and forestry [7]. When considering A. artemisiifolia, the main problem is the health risk for human population. Some invasive species may be promoted by climate change (e.g., [8]) due to characteristics that facilitate rapid range shifts (e.g., short time to maturity and low seed mass) and due