Paper No. 78-9
Presentation Time: 10:00 AM
TESTING THE LAW OF CONSTANT EXTINCTION WITHIN MARINE ADAPTIVE ZONES
ORZECHOWSKI, Emily A.1, HEIM, Noel A.
2, KNOPE, Matthew L.
3, PAYNE, Jonathan L.
2 and FINNEGAN, Seth
4, (1)Department of Integrative Biology and Museum of Paleontology, University of California, Valley Life Sciences Building, Berkeley, CA 94720-3140, (2)Department of Geological Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, CA 94305, (3)Department of Biology, Stanford University, Stanford, CA 94305, (4)Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, Valley Life Sciences Building, Berkeley, CA 94720-4780, eaorzechowski@berkeley.edu
The Law of Constant Extinction states that the probability of extinction is independent of lineage age. The apparent age-independence of extinction risk served as the basis for Van Valen’s (1973) Red Queen’s hypothesis, which posits that within an “adaptive zone” (Simpson 1944) the effective environment deteriorates at a stochastically constant rate. However, many subsequent analyses yield results incompatible with the Law of Constant Extinction. There exist two possible explanations for this discrepancy: (1) the Law of Constant Extinction does not apply or (2) previous analyses have focused on taxonomic groups rather than the eco-evolutionary adaptive zones for which the law was conceived. Investigating the dependence of extinction risk within objectively defined adaptive zones is therefore critical to assessing the actual prevalence of Red Queen dynamics across evolutionary time.
In this study, we used the Paleobiology Database and a new ecospace database to analyze age selectivity of genus extinctions within marine adaptive zones, which we defined operationally as genera belonging to the same taxonomic class and sharing the same coding within Bush and Bambach’s (2007) classification of ecospace (i.e. sharing tiering, motility, and feeding ecologies). We used multiple logistic regression to test for association between genus age and extinction risk within each of 74 Phanerozoic stratigraphic stages. We analyzed genus extinction patterns separately in each adaptive zone, and included geographic range and species richness as potentially confounding age-dependent risk factors. We find that a substantial proportion of the age-dependent extinction signal detected by an earlier analysis (Finnegan et al. 2008) can be explained by the mixing of genera from different adaptive zones. Our results do not provide direct support for the Red Queen’s hypothesis but do suggest that the Law of Constant Extinctions, as originally defined, may be valid in many cases.
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