In the Light of Evolution Volume II: Biodiversity and Extinction (2008) / Chapter Skim
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11 Dynamics of Origination and Extinction in the Marine Fossil Record--JOHN ALROY
11 Dynamics of Origination and Extinction in the Marine Fossil Record--JOHN ALROY
Pages 207-226
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From page 207... ...
Second, very high extinction rates are followed by equally high origination rates. The two relationships predict that the rebound from the current mass extinction will take at least 10 Myr, and perhaps 40 Myr if it rivals the Permo-Triassic catastrophe.
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From page 208... ...
Even though this view is very inconsistent with such well-documented patterns as rapid rebounds from mass extinctions (Kirchner and Weil, 2000b; Erwin, 2001; Foote, 2003) , a basic logistic model assuming a single equilibrium point (Sepkoski, 1978)
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From page 209... ...
The strong statistical patterns reported here show that diversity does not increase exponentially without constraints and therefore make it possible to predict the rebound from the current mass extinction in strict quantitative terms. First, however, a series of other major hypotheses concerning mass extinctions and diversity dynamics need to be addressed.
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From page 210... ...
. The former problem has been fully resolved by sampling standardization of the data and by the use of rate equations that are robust to edge effects
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From page 211... ...
FIGURE 11.1 Per-interval instantaneous origination rates (A) and extinction rates (B)
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From page 212... ...
More detailed analyses are called for, but the difference is so large that it could easily explain the trend. Big Five Mass Extinctions The apparent existence of five major peaks in extinction rates is another key finding in the literature on Phanerozoic marine diversity (Raup and Sepkoski, 1982; Raup, 1986)
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From page 213... ...
. Thus, not only are there no distinct classes of major origination or mass extinction events, but there is minimal evidence that extinction rates are more volatile than origination rates.
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From page 214... ...
. In summary, it is a matter of taste whether to speak of the Big Five, the Big Three, or just the Big One, but one way or another major mass extinctions are truly very rare.
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From page 215... ...
. EQUILIBRIAL DYNAMICS Density Dependence The lack of periodicity in turnover rates does not imply that these rates are random and therefore does not imply that the diversity curve evolves randomly.
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From page 216... ...
. The two strong relationships are crucial, because they are responsible for the suggested equilibrium: high diversity will be brought down by high extinction rates, and large extinctions will be compensated by high origination rates.
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From page 217... ...
(B) Correlation between extinction rates in one interval zpq9990837800003.g.eps and origination rates in the next.
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From page 218... ...
. Meanwhile, the assumption of slowly changing origination rates is consistent with slow sorting of large clades that have distinctive turnover rates (Gilinsky, 1994)
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From page 219... ...
An extinction-origination correlation is indeed present, but the pattern is different from expected under the hypothesis that niches need to be reconstructed. First, very high origination rates come immediately after what are clearly rapid mass extinctions (Fig.
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From page 220... ...
The second step is to model origination as a function of past extinction. However, origination rates cannot be predicted solely from the contemporary extinction rates produced in the first step without producing pathological results, because the initially low extinction rates would imply low, not high, origination rates.
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From page 221... ...
When diversity is high for any reason, extinction rates rise both in the same interval and the immediately following ones. When diversity is low because of a preceding major mass extinction, origination rates rise.
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From page 222... ...
The only clear-cut processes that could create such responses are ecological interactions, such as competition and predation, that affect the overall probability of speciation and extinction. Presumably, these interactions influence attributes of species, such as population size, population density, and geographic range size, that are not properties of individual organisms regardless of whether one wants to call them emergent or aggregate (Jablonski, 2000)
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From page 223... ...
remove the edge effects by ignoring ranges and focusing instead on occurrence data that show which fossil taxa are actually sampled in which time intervals. These methods are only made possible by the existence of occurrence-based relational databases, and could not have been applied to the Phanerozoic marine record before the development of the Paleobiology Database (Alroy et al., 2001)
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From page 224... ...
Madin for helpful comments on an early draft. I thank the National Science Foundation for recognizing the importance of the Paleobiology Database and an anonymous donor for funding the database.
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From page 225... ...
Dynamics of Origination and Extinction in the Marine Fossil Record / 225 Synthesis, a center funded by the National Science Foundation and funded by National Science Foundation Grant DEB-0072909, the University of California, and the Santa Barbara campus. This is Paleobiology Database publication no.
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