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.