Recoveries Are Also Spatially Complex

Most research on spatial dynamics has focused on extinctions, but evidence is accumulating for a spatial component to recoveries as well. The raw evolutionary material that survives the mass extinction filter is crucial in shaping the postextinction world. However, the evolutionary novelties and the ecological restructuring that emerge in the postextinction interval, including the little-appreciated process of sorting survivors into winners and losers (Jablonski, 2002), may be as important as the extinction filter in determining the long-term trajectory of individual clades.

Returning to the spatially explicit form of the fundamental macroevo-lutionary equation, we can partition a regional biota after, e.g., the K-T mass extinction, into survivors of the event, locally evolved new taxa, and invaders. The four regions with the best marine molluscan records in the 10 Myr after the K-T event differ significantly in their recovery dynamics (Jablonski, 1998). For example, the North American biota was much more subject to invasions during the early stages of the post-Cretaceous recovery, and contains significantly fewer novel taxa, than the other regions. However, the survivor components (the regional extinction intensities) are indistinguishable among regions (Fig. 10.3).

Spatial heterogeneity has recently being detected for other recoveries as well. For example, after the end-Ordovician extinction «445 Myr ago, Baltica, a continental plate centered «30° south, had the lowest extinction intensity and the lowest invasion intensity among marine invertebrates, whereas Laurentia, which was straddling the equator, showed a tighter bunching of the three faunal components (Krug and Patzkowsky, 2007). Spatial heterogeneity in recovery from the huge end-Permian extinction has been reported for some groups [e.g., brachiopods and bivalves (Chen et al., 2005; Bonuso and Bottjer, 2008)] but not others [e.g., ammonoids (McGowan, 2005), but see Brayard et al. (2006)].

The K-T example is striking in its failure to show the inverse relation between local survivorship and invasion that is generally expected [e.g., Fridley et al. (2007)] and is observed for the end-Ordovician. One

200 / David Jablonski

(Survival Origination ^Invasion

N America N Europe N Africa Pakistan

FIGURE 10.3 Regional variation in molluscan recovery dynamics after the K-T extinction. Four postextinction biotas are partitioned into their surviving, newly originating, or invading components. The Gulf and Atlantic Coastal Plain was subject to significantly more intense invasion than the other three regions (95% binomial confidence intervals). See Jablonski (1998) for details.

N America N Europe N Africa Pakistan

FIGURE 10.3 Regional variation in molluscan recovery dynamics after the K-T extinction. Four postextinction biotas are partitioned into their surviving, newly originating, or invading components. The Gulf and Atlantic Coastal Plain was subject to significantly more intense invasion than the other three regions (95% binomial confidence intervals). See Jablonski (1998) for details.

can speculate that this difference is attributable to the greater proximity of North America to the K-T impact site in Yucatan, but how does that proximity translate to great invasions without imposing exceptional extinction? Qualitative, rather than quantitative, losses might account for the greater invasibilty of North America, but this hypothesis has not been tested. Alternatively, the correlation between extinction intensity and subsequent invasion may begin to break down above some threshold extinction level. One clue may come from another spatial difference: the short-lived evolutionary burst of a few taxa in North America [''bloom taxa'' of Hansen (1988)] that is evidently absent in northern Europe, North Africa, or Pakistan and India (Jablonski, 1998). North America's bloom taxa and the invasion pulse are almost certainly linked, presumably indicating a more profound ecological and evolutionary disturbance in North America than elsewhere, but this needs to be examined more closely. Whatever the ultimate cause, the fossil record pinpoints a theoretically interesting but pragmatically disquieting gap in our understanding of the extinction-invasion relationship. Given the current acceleration of both processes, and the pressure to establish reserves for remaining biodiversity, this relationship deserves more attention.

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