Week 8: Evolutionary Dynamics (continued)

Paper for Thursday: Ecospace Utilization and Guilds in Marine Communities through the Phanerozoic (1983)

Commentary author: Andrew M. Bush

Andrew Bush is currently the associate professor of Paleobiology at University of Connecticut’s Department of Ecology & Evolutionary Biology and Center of Integrative Geosciences in Storrs, CT. He received his PhD from Harvard University. His main interests lie in marine biodiversity and paleoecology, with a focus on the late Devonian extinction and its stratigraphy. Bush is particularly interested in studying ecospace filling through the fossil record, and he has published many papers on the subject with Bambach.

Paper author: Richard K. Bambach

Richard Bambach’s greatest gift to the paleontological community was his 1983 paper, “Ecospace Utilization and Guilds in Marine Communities through the Phanerozoic,” in which he uses the idea of classification of marine metazoans and their guilds into cubes that can then be studied for signs of ecospace diversification through time. He’s been a professor or visiting/guest professor at a long list of schools, including Virginia Tech, Smith College, University of Chicago, and Harvard University. After his retirement, he worked at the Botanical Museum at Harvard, and is now a research associate at the Smithsonian. He has been honored with, among others, the Paleontological Society Medal and the Raymond C. Moore Medal.

Cliffnotes

Sepkoski presents in a set of papers that marine families increase in diversity across the Phanerozoic (save for a few exceptions). It is on these papers that Bambach bases his hypothesis: an ecologic component is driving evolution – use in ecospace had to change to drive this increasing diversity curve. His evidence lies in the increase in species richness per habitat through time.

Bambach uses “guild analysis” to answer this question. First, he looks at the big picture: early metazoans in the Paleozoic had low diversity and exploited very little ecospace. Mesozoic-Cenozoic fauna increased in infaunal and carnivorous habits, as well as in diversity. This means the overall increase in diversity can be correlated with an increase in ecospace utilization.

The next step is paleocommunities. Bambach defines his “guild” with three variables: Bauplan, space utilization, and food source (forms a “cube,” or guild). He compares mid-late Paleozoic with Neogene fauna. The data show an increase in number of guilds and species in the Neogene, and lower species richness and a constant number of guilds in the Paleozoic (“diversity equilibrium” = little change in community structure).

A peculiar pattern also emerges: in large communities with lots of species, many species are portioned out into large guilds. This might mean that the data does not support the hypothesis that guild number increases with diversity. However, it is more likely that these guilds are just a “superguild” of smaller, poorly-defined guilds that have been lumped together. 
Some questions to think about: What kinds of biases can come up when doing a study like this? Bambach has already listed a few for us. Do you think Bambach's three variables for marine guilds are all-encompassing or would you exchange any of them?