Paper 39 by K. Sullivan

Paper 39

Sepkoski, J.J. 1988. Alpha, beta, or gamma: where does all the diversity go?

Paleobiology 14:221-234.

Blog by Kaitlyn Sullivan

Paper Author: Jack Sepkoski

(Commentary by Peter Wagner)

Jack Sepkoski Jr.

·       Professor of Paleontology at the University of Chicago

·       PhD from the Harvard University

·       Passed away in 1999

“During the 1980s, using rigorous statistical analyses of the fossil record, Sepkoski and his Chicago colleague David Raup put forth the controversial theory that catastrophic extinctions of marine animals may have occurred approximately every 26 million years during the past 250 million years of Earth's history. These periodic events also included the extinction of the dinosaurs 65 million years ago. The extinctions previously were thought to have been random events.

The theory helped open the possibility that mass extinctions both on land and in the oceans were caused by some force external to Earth, such as catastrophic comet and asteroid impacts of the type that inspired the films "Deep Impact" and "Armageddon" and inspired the popular Shriekback song "Nemesis." These findings prompted a major interdisciplinry research effort on extinction events in the fossil record.”

Koppes, Steve. "Paleontologist J. John Sepkoski Jr., 1948-1999." NASA. NASA, 4 May 1999. Web. 02 Apr. 2017.

Peter Wagner

·       Curator of Paleozoic Molluscs at the Smithsonian National Museum of Natural History

·       Ph.D. Geophysical Sciences University of Chicago 1995, Thesis Title:  "The generation and maintenance of morphologic and phylogenetic diversity among early gastropods."

·       M.S. Geological Sciences Michigan State University 1990, Thesis Title:  "Phylogenetic analysis of the Lophospiridae (Gastropoda: Pleurotomariina) of the Ordovician and Silurian."

·       B.S. Geological Sciences Michigan State University 1989

·       B.S. Anthropology/Zoology University of Michigan, Ann Arbor 1986

“The fundamentals of my research revolve around phylogenetic relationships among Paleozoic mollusks. The majority of my work has been on Cambrian - Devonian anisostrophic gastropods, although I've started dabbling with bellerophont gastropods also.  I also have worked with a more obscure and entirely extinct group, the Rostroconchia.

The primary purpose of this phylogenetic work is to provide a template for the macroevolutionary studies discussed below. However, it also has resulted in an extensive taxonomic revision of Early Paleozoic gastropods.”

Wagner, Peter. "Department of Paleobiology." Peter Wagner. N.p., n.d. Web. 03 Apr. 2017.

Summary

In the commentary, Wagner states that “this particular study directly examines how basic macroecological parameters (environmental and biogeographic differentiation of faunas) affects basic macroevolutionary parameters (i.e., global diversity and diversification over time).”  Wagner went on to distinguish the difference between alpha-diversity, beta-diversity, and gamma-diversity.  Alpha-diversity is defined as the “richness within particular habitats”, beta-diversity is “differentiation among adjacent environments and regions”, while gamma-diversity can be defined as “differentiation among different faunal provinces”.  Alpha diversity measure the division of ecological resources among species.  Beta diversity, is used to measure the turnover rate of “species composition along environmental gradients”.  Gamma diversity is similar to beta diversity, however the spatial scales being measured are much larger and “reflects the degree of provinciality or endemicity in the biota”.

                  As stated in his abstract, Sepkoski objective was to investigate “how variation in alpha and beta diversity influenced global diversity through the Paleozoic, and especially during the Ordovician radiations”.  To investigate this, Sepkoski, used “a data set consisting of 505 faunal lists distributed among 40 stratigraphic intervals and six environmental zones”.  Based on these data, finding suggest the following:

1.     When measured at the genus level, global taxonomic diversity increased by a factor of four during the Ordovician radiation.

2.     Alpha diversity can account for a small portion of this, exhibiting a 50 to 70 percent increase of species and genus during the Ordovician

3.     Global diversity is also influenced by beta diversity, increasing soft-bottom communities during the Ordovician by approximately 50 percent at the generic level.

4.     Increase in beta diversity is proportional to increasing habitat specialization of taxa as evolutionary fauna during the Paleozoic replaced fauna from the Cambrian period.

5.     Any changes in global diversity that cannot be attributed to changes in alpha or beta diversity is likely not the result of gamma diversity during the Ordovician but likely due to “hidden” forms of beta diversity, (i.e. “the appearance or expansion of new community types”).