Consolidating invasion paradox with a beta-diversity based theoretical model
Contradicting results from observational and experimental studies on native-exotic diversity relationships— the “invasion paradox”— have prompted several theories to explain the inconsistent patterns observed. Although several processes that generate either negative or positive native-exotic diversity associations have been identified, there is no single general model that is able to explain why these patterns vary with scale and across ecosystems.
Here, we present a theoretical model using the level of heterogeneity of species assemblages (i.e. beta-diversity) in an area, instead of scale, to resolve the contradictions observed in native-exotic diversity patterns. The beta-diversity model predicts the association between native and exotic diversity based on three assumptions: (1) there is a positive correlation between native and exotic beta-diversity; (2) once beta-diversity passes a certain threshold, it drives trends observed in the cumulative diversity of the area studied, masking patterns between native and exotic diversity driven by local processes and revealing a positive association; and (3) increasing scales will increase beta-diversity past that threshold. Under this model, current theories on native-exotic diversity relationships are unified by presenting a scenario in which they are all possible without being contradictory. The beta-diversity model has the potential to broaden opportunities to better understand the relationship between native diversity and invasibility, while also providing insight into the processes that influence biodiversity, community assemblage, and biogeographical gradients at the global scale.