Stage dependence of Elton’s biotic resistance hypothesis of biological invasion

Elton’s biotic resistance hypothesis posits that species-rich communities are more resistant to invasion. Yet, there is evidence that species richness alone may not fully explain community resistance, as phylogenetic and functional richness, along with environmental factors and human-induced disturbances, also play pivotal roles. Additionally, it remains unknown how these factors collectively affect plant invasion as alien species progress along the introduction-naturalization-invasion continuum. For 12,056 local plant communities of Central Europe, we investigate how these factors affect the presence and richness of alien species at different stages along the invasion continuum. Our study reveals varying effects of these factors on the presence and richness of alien species at different invasion stages, highlighting the complexity of the invasion process. Specifically, we demonstrate although species richness and functional richness of resident communities had mostly negative effects on alien species presence and richness, the strength and sometimes also direction of these effects varied along the continuum. By uncovering the stage-dependent effects of these factors, our study not only offers a more nuanced understanding of Elton’s biotic resistance hypothesis but also suggests that other invasion hypotheses should be carefully revisited given their potential stage-dependent nature.