appreciation of the extent and possible roles of phylogenetic niche conservatism, and the development of better analytical tools, especially to infer historical biogeography [e.g., Ree et al. (2005)] and rates of diversification [e.g., Chan and Moore (2005) and see Ricklefs (2007a)], the stage is clearly set to reintegrate historical factors into such explanations. These are in no way meant to replace environmental explanations, but rather to complement them and connect them to the speciation, extinction, and migration processes that ultimately underlie such patterns (Wiens and Donoghue, 2004).
The argument I am making in several ways parallels the view set out by Gould and Lewontin (1979) on the study of adaptation. They argued that adaptation is caused not by the environment, but by the interaction of the environment with the evolved, organismic substrate. They viewed the substrate in this interaction as determining the outcome just as much as the environmental pressures and argued that these should be treated as equal partners in the causal explanation. Likewise, I am arguing that it is the action of changing environments on the evolved ecological characteristics of lineages that results in the patterns of biodiversity we observe today, and, furthermore, that the role that these lineages play is every bit as interesting and powerful in determining the outcome. In short, I am agreeing with Robert Ricklefs (2004) that we should “raise regional and historical factors to equal footing with local determinism in their influence on the diversity–environment relationship and geographical patterns of diversity in general.” Fortunately, whereas the integration of phylogenetic knowledge into such explanations once seemed unnecessary, and for a time seemed interesting but impractical, now it seems virtually inevitable.
Finally, it is worth reflecting on the future of biodiversity in light of the basic principle highlighted here. In the deep evolutionary past, corridors for the movement of biotas within and among continents were opened or shut based primarily on the relative position of landmasses, geologic particulars (e.g., the location and orientation of rivers and mountain ranges), and climate changes. Moving into the future, anthropogenic habitat fragmentation adds a complicating new variable to the equation, as does the current rapidity of climate change and the wholesale movement of species by humans. Depending on the vagility of the organisms involved, the habitat discontinuities imposed by humans may limit the impact of the migration of preadapted species in community assembly, which I believe has played such an important role in the past. The consequences for community composition, structure, and function are unclear. One possibility is that anthropogenically isolated habitats will remain, at least for a time, “empty” of species from surrounding areas that might be well adapted to them. On the other hand, barriers to migration might create circumstances