Synthesis.

Abstract

Abstract About 1100 studies focusing on 12 major invasion hypotheses have been analysed in Chapters 8-16 of this book. A network of these 12 hypotheses, in which topically similar hypotheses are connected, was presented in Chapter 7. We here combine and synthesize these previous chapters, colour coding the hypothesis network depending on the level of empirical support of each hypothesis. Overall, six of the 12 hypotheses were supported by the majority of available empirical studies, three hypotheses were questioned by the majority of studies, and empirical studies were undecided for the three remaining hypotheses. The three questioned hypotheses were: evolution of increased competitive ability (EICA), biotic resistance and the tens rule. On the basis of these findings, we propose an alternative hypothesis network in which the biotic resistance hypothesis and the tens rule are replaced by revised hypotheses that are better empirically supported, and the EICA hypothesis is abandoned because the better empirically supported shifting defence hypothesis already is a refinement of this hypothesis. The revised hypothesis network therefore consists of 11 major hypotheses. Most studies analysed in this book focused on terrestrial plants in affluent countries, whereas other taxonomic groups, habitats and other countries are underrepresented in the invasion literature. Observational studies currently dominate the field. We further found that the level of empirical support has declined over time for some but not all focal hypotheses. The hypothesis network featured here is provided online, where it is also connected to the empirical data analysed in this book. This website is envisioned as the initiation of an advanced online tool that grows beyond invasion biology and should cover different scientific disciplines such as community ecology, biodiversity science and evolutionary biology. It is meant to visualize the major concepts, ideas and hypotheses in these disciplines including their links and connections, thus featuring a large structured network that is connected to the data generated in these disciplines.