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In the Light of Evolution: Volume II—Biodiversity and Extinction
regional diversity can accrue either by in situ origination or invasion (immigration). The high present-day rate of anthropogenic introductions in marine systems will likely outstrip regional evolutionary recovery by an order of magnitude or more, exacerbated of course by other anthropogenic stresses [e.g., Ruiz et al. (2000), Jackson et al. (2001), Lötze et al. (2006)]. This paleontological perspective on regional marine biodiversity adds another element to the urgency of slowing anthropogenic homogenization of marine biotas, if the diversification debt of some regions indeed makes them more susceptible to invasions (and see below).
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 macroevolutionary 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