What we know and don’t know about invasive vertebrates in Europe

Invasive species are those that have been introduced to regions beyond their native range, established in the wild, and spread substantially from their point of introduction (Blackburn et al., 2009; Lockwood et al., 2007). They can diminish biodiversity, introduce diseases, and cause further ecological problems and economic costs (Kettunen et al. 2009). Although a few early publications about invasive species date back to the 19th century (Darwin, 1859; reviewed in Cadotte, 2006), publications have only become numerous since the late 20th century (Richardson and Pyšek, 2008). Many hypotheses about invasive species have been proposed, but only recently has it become possible to test them adequately, as sufficient studies and data were not available before. A prominent example for a project that collected data on invaders in Europe is DAISIE (2009). With sufficient studies and data now available, invasion biology has entered a new stage where existing hypotheses can be rigorously tested, and those that fail these tests may be modified or replaced. Another challenge that invasion biology is currently facing is the need to build bridges with related disciplines (Davis, 2009). To illustrate these challenges and their implications for invasive species management (Clout and Williams, 2009), I outline to what degree we can currently answer the following questions, which have guided research on invasive species for decades (Drake et al., 1989): (1) How many species become invasive in a given region? (2) Which species become invasive? (3) Which regions are especially susceptible to invasive species? I will focus on invasive vertebrates in Europe, but for comparison, I will also mention other taxonomic groups and continents