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10 Extinction and the Spatial Dynamics of Biodiversity--DAVID JABLONSKI
Pages 189-206

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From page 189...
... Evolutionary recoveries also exhibit spatial dynamics, including regional differences in invasibilty, and expansion of clades from the tropics fuels at least some recoveries, as well as biodiversity dynamics during normal times. Incumbency effects apparently correlate more closely with extinction intensities than with standing diversities, so that regions with higher local and global extinctions are more subject to invasion; the latest Ceno zoic temperate zones evidently received more invaders than the tropics or poles, but this dynamic could shift dramatically if tropi Department of Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637.
From page 190...
... , is important in many situations, from biotic responses to Pleistocene climate cycles and ongoing climate changes to recoveries from mass extinctions. However, this form is even more difficult to apply rigorously without historical data, and my emphasis here will be on the fossil record.
From page 191...
... . However, our growing knowledge of living and fossil bivalves, including the taxonomic, preservational, and geographic factors that can distort their fossil record, makes this group an excellent vehicle for integrating present-day and paleontological diversity dynamics.
From page 192...
... Every event seems to show some degree of selectivity, but one factor that seems to have promoted survival for most major groups and most mass extinctions is broad geographic distribution at the clade level (i.e., genera) , regardless of species-level geographic ranges.
From page 193...
... (C) Significant inverse relation between extinction intensity and the number of biogeographic provinces occupied by bivalve genera during the K-T extinction (Spearman rank test, P < 0.01)
From page 194...
... Multifactorial analyses corroborate the importance of clade-level distribution in determining survival during mass extinctions and show the value of testing for interaction among factors. For example, if variables are treated independently in the updated K-T dataset, geographic range remains the most important factor in clade survivorship, but species richness also appears to play a significant role (and body size is insignificant as a survivorship predictor)
From page 195...
... . This configuration is much more demanding of the data, so that sparse or noisy data may fail to capture that shallower A "Background" Extinction B Mass Extinction Extinction Intensity Extinction Intensity Geographic Range Geographic Range FIGURE 10.2  The inverse relation between geographic range and extinction risk appears to vary with severity of extinction.
From page 196...
... Organismic traits such as dispersal ability and ecological strategy must play a role, but interactions with biogeographic context, clade history, and many other factors, including the way that clades extend their ranges by speciation across barriers, serve to decouple geographic ranges at the species and clade levels. For example, the geographic ranges of the 213 marine bivalve genera present today at shelf depths on the eastern Pacific margin from Point Barrow, Alaska to Cape Horn, Chile are not significantly related to the median or maximum ranges of their respective constituent species (Jablonski, 2005)
From page 197...
... For example, marine bryozoan genera with complex colonies suffer more severely during mass extinctions than simple genera, but colony complexity is also inversely related to genus-level geographic range (Anstey, 1978, 1986) , which may well be the ultimate basis for differential survival during the end-Ordovician mass extinction.
From page 198...
... .] However, the spatially explicit form of the fundamental macroevolutionary equation shows that
From page 199...
... , 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.
From page 200...
... 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.
From page 201...
... One of the most pervasive spatial patterns of invasions, seemingly independent of mass extinction events, underlies the marine latitudinal diversity gradient, wherein morphologies, species, and higher taxa are richest in the tropics and decline toward the poles. Although the gradient has been known for a long time and is documented for many groups and regions, the processes underlying this pervasive biodiversity pattern remain poorly understood (Hillebrand, 2004; Mittelbach et al., 2007)
From page 202...
... A preliminary test of these alternatives did find a humped extinction pattern with latitude for Northern Hemisphere bivalve genera in the latest Cenozoic, with global plus regional extinction totaling ≈9% in the tropics, ≈20% in the temperate zone, and ≈12% in the Arctic (Valentine et al., 2008)
From page 203...
... First, broad geographic range probably always buffers clades from extinction, but it becomes most important and clear-cut as the suite of other factors that enhance species and genus survival during normal times become ineffective. It is not yet clear whether the selectivity regime changes steadily with increasing extinction intensity or as a step function (Jablonski, 2005)
From page 204...
... Second, the fossil record is rich in regional extinction events of intermediate intensities, and these can provide insights into present-day biodiversity issues. For example, the Cenozoic history of today's biodiversity hotspots and coldspots (relative to expectations for their latitudes, for example)
From page 205...
... More generally, spatially explicit approaches to the fossil record have great potential for new insights into diversity dynamics, not just in the geologic past, but in the present day as well. The integration of paleon
From page 206...
... 206  /  David Jablonski tological and neontological insights takes on special urgency with the acceleration of extinction rates in the modern world, and the incorporation of the spatial dimension offers a powerful vehicle for that integration. ACKNOWLEDGMENTS I thank John Avise, Francisco Ayala, and Stephen Hubbell for inviting me to participate in this colloquium; J


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