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TABLE 10.1 Testing Models for Bivalve Genus Survivorship During the K-T Mass Extinction

Models

No. of Parameters

AIC

Weight

P

G** + R + B*

4

347.9

0.58

0.002/0.85/0.03

Geographic range***

2

348.6

0.40

e-6

Species richness***

2

356.2

0.02

0.0001

Body size

2

373.5

e-6

0.94

NOTES: When geographic range (G), species richness (R), and body size (B) are analyzed as independent factors, G is the most important factor, but R is also significant. When the three are analyzed together, R is not a significant factor. Note that the combined model is not significantly better than geographic range alone according to the AIC (for model selection, which essentially weighs the adding of parameters against the improved explanatory power of each model).

*P < 0.05;

**P < 0.01;

***P < 0.001.

and extinction risk varies with extinction intensity is not known and is difficult to assess. The few available data suggest that the relation between extinction probability has a steep slope during times of low extinction intensity, with the most widespread genera suffering negligible extinction at those times (Payne and Finnegan, 2007; Powell, 2007a) (Fig. 10.2A). The simplest view would be that perturbations generally operate at too small a spatial scale to affect these most widespread elements of the global biota. In the major mass extinctions, the y-intercept increases, so that a greater fraction of taxa are lost from all range classes, and the slope probably decreases (Fig. 10.2B). This configuration is much more demanding of the data, so that sparse or noisy data may fail to capture that shallower

FIGURE 10.2 The inverse relation between geographic range and extinction risk appears to vary with severity of extinction. Conceptual model for this variation, such that both slope and intercept may change between times of background (A) and mass extinction (B).

FIGURE 10.2 The inverse relation between geographic range and extinction risk appears to vary with severity of extinction. Conceptual model for this variation, such that both slope and intercept may change between times of background (A) and mass extinction (B).



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