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capacities (Raup, 1972; Carr and Kitchell, 1980) or coupled logistic models. One example is Sepkoski’s description of the diversity patterns of the Cambrian, Paleozoic, and Modern evolutionary marine faunas (Sepkoski, 1984); see Alroy (2004) for a critique. The alternative class was labeled expansionist by Benton and Emerson (2007) as it does not invoke an explicit carrying capacity, or it suggests that it may never have been reached, possibly because of recurrent disturbances (Valentine and Walker, 1986; Benton, 1997; Stanley, 2007). The utility of a global carrying capacity is extremely doubtful (Benton and Emerson, 2007; Stanley, 2007; del Monte-Luna et al., 2004).

The critical question for understanding biotic recoveries is in understanding how the network of ecological and environmental interactions facilitates the construction of biodiversity, which is a network issue, not one that is properly addressed by borrowing models of population demography. Thus understanding the growth of taxic diversity after mass extinctions requires understanding the ecological relationships that build these networks, including both the positive feedbacks (such as niche construction and environmental engineering) and the more commonly invoked negative feedbacks such as competition. At present we have no theoretical models applicable to this problem.

Our knowledge of the response of most of the other metrics during postextinction biotic recoveries is generally even more fragmentary than our knowledge of their behavior during the extinctions. The highly uneven branching structure of most phylogenetic trees reflects uneven rates of diversification along different branches of a tree and the loss of some branches through extinction (Nee and May, 1997). With the exception of the substantial literature on the relationship of the bird and placental mammals across the Cretaceous-Tertiary boundary, there are relatively few large-scale phylogenetic studies of post-mass extinction biotic recoveries. Despite this absence, many evolutionary radiations of single clades are well studied during biotic recoveries. Examples include trilobites in the Late Cambrian, ammonoids after the Late Devonian, end-Permian, and end-Triassic episodes, and quillworts in the Early Triassic. As discussed above, where it has been studied among marine taxa, morphologic disparity rapidly expands after mass extinctions (Erwin, 2007a). Significantly for the structure of these recoveries, disparity often expands into different dimensions than were occupied by the preextinction taxa, demonstrating that recoveries have their own dynamic and are not simply the refilling of previously occupied morphospace. Without detailed studies, my impression is that architectural diversity as measured by the reappearance of framework-bound reefs is often one of the last segments of diversity to rebound, and in almost all cases (the Early Jurassic is a possible exception) does so by the appearance of new groups. This apparent delay could reflect



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