Revisiting a Darwinian framework for invasion biology: Global invasion patterns and the evolutionary sophistication of regional biotas

Background/Question/Methods

One of the first perspectives on biological invasions was articulated by Darwin, who argued that invasions are to be expected because natural selection adapts species "only in relation to the degree of perfection of their associates", leaving them vulnerable to "being beaten and supplanted by naturalised productions from another land".  A century and a half later, we find that this perspective has been largely neglected in favor of mechanisms related to the concept of imbalanced ecosystems as articulated by Charles Elton and others.  Here we formulate a renewed framework for invasion biology based on the action of natural selection in historically isolated populations, which inevitably leads to global evolutionary disequilibria in the efficiency at which organisms of similar habitats convert resources into offspring.  Once long-distance dispersal barriers are removed by human intervention, some species will have superior fitness for a given set of environmental conditions, thus becoming 'invaders'.  Critically, we show that there are properties of a biotic region that reflect this process of greater evolutionary sophistication, in particular a biota's phylogenetic diversity, which is in turn strongly predictive of global invasion patterns.

Results/Conclusions

Using alien floras of the Eastern U.S., China, the Czech Republic, New Zealand, and California, combined with family-level phylogenies for the world's major floristic regions, we show that a source flora's phylogenetic diversity is a highly significant predictor of invasion potential, explaining as much as 70% of the variation in regional invasion patterns.  Biases in the net direction of biotic interchange across marine assemblages connected by man-made canals also attest to the predictive role of phylogenetic diversity in global invasion patterns.  We conclude that the study of biological invasions should be focused upon species differences that are rooted in divergent evolutionary histories—a Darwinian approach—in addition to the current modal Eltonian perspective that emphasizes novel evolutionary context or novel ecological processes arising in the introduced range.