Taxonomic survivorship curves were tabulated by Van Valen

Taxonomic survivorship curves were tabulated by Van Valen -...

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Taxonomic survivorship curves were tabulated by Van Valen, U. Chicago (see figure below). Horizontal axis in the number of years that a group has survived (could be 50 Myr. in the Cenozoic or 50 Myr. in the Paleozoic); vertical axis in the log of the number of taxa that survived for the stated number of years. The ~ straight lines indicate that a constant proportion of the taxa are becoming extinct at various stages of duration, which Van Valen interpreted to mean that the probability of extinction is independent of age of taxon . This further implies that taxa are not becoming better adapted (if one defines increased adaptedness as a decreasing probability of going extinct). Note that these survivorship curves are different than the ones presented for moluscs and carnivores.
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Unformatted text preview: Note also that the graphs do not imply that there is a constant extinction rate per unit time. The approximately linear relationship indicates that the taxa with a long duration do not appear more resistant to extinction . Van Valen proposed the Red Queen hypothesis to account for the pattern of approximately linear survivorship curves. Van Valen hypothesized that 1) the environment is continually deteriorating (~ changing so that current adapted state is no longer applicable), 2) organisms have to adapt continually, i.e., you have to " run to stay in place " like the Red Queen said to Alice in Through the Looking Glass (Alice in Wonderland)....
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This note was uploaded on 11/06/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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Taxonomic survivorship curves were tabulated by Van Valen -...

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