Sometimes the questions are complicated and the answers are simple: null models in invasion ecology

Background/Question/Methods

One of the many contributions that Dan Simberloff has made to the fields of ecology and biogeography is his insistence that research conclusions be based on firm deductive reasoning. This perspective is perhaps most clearly found within the debates surrounding the role of chance in structuring ecological communities, especially on islands. My own research was profoundly shaped by this perspective as my early research related to the role of inter-specific competition in structuring island bird communities. With his (later) input and encouragement, I transferred this perspective into the context of invasion science. Here I review evidence that the number of initial founding individuals of a non-native species (propagule pressure) plays a primary role in determining the long-term persistence of these populations.

Results/Conclusions

I will show that the relatively simple, chance-oriented mechanisms that underlie this relationship serve as a useful null model for several more complex spatial and temporal patterns in numbers of established non-native species. Incorporation of this null model into invasion experiments and forecasts clarifies mechanisms, reveals clear policy priorities, and guards against inferential mistakes. I also highlight areas of invasion ecology that are under-studied but rich with possibilities in regard to both propagule pressure and the regular use of null models within invasion ecology.