Paper 21

Pg 377

Paper 21- Graham 1986

Graham R.W. 1986. Response of mammalian communities to environmental changes during the late Quaternary. Pages 300-313 in J. Diamond and T.J. Case, eds., Community Ecology. Harper and Rowe, New York

Blog Author: Angel Sumpter

Blurb Author: S. Kathleen Lyons

●     B.S. Wayland Baptist University, 1991

●     Ph.D. at University of Chicago in 2001

●     Currently an assistant professor of biological sciences at the University of Nebraska.

●     “I am interested in the factors affecting and controlling species diversity at multiple scales across both space and time. Moreover, I am particularly interested in the effects of global climate change on species diversity and use the fossil record of mammals over the last 40,000 years to evaluate how current changes in global climate may affect diversity patterns in the future. Because it provides a useful way to compare modern species and communities to fossil species and communities, I focus on the similarities and differences in macroecological patterns across space and time.”

Paper Author: Russell W. Graham

●      Professor, Museum Director

●     Ph.D., University of Texas at Austin, 1976

●     Research Interest: Vertebrate Paleontology, Quaternary Vertebrate Paleontology, Taphonomy, and Neotoma Paleoecological Database.

Main Question

●     Background

○     Approximately 18,000 years most of the midwestern US and Canada were covered in ice. Once ice started to melt about 8000 years afterwards, ice glaciers only occupied miniscule portions of Canada. Over time this continued during the Pleistocene. Data shows various stages where ice was high, then lower, and somehow alternated between the two. For this reason various species shifted their ranges.

●     Question

○     How ancient are modern ecological communities?

○     Is it likely that species that coexist today have had a long continued history of opportunity for coevolutionary adjustments to each other?

Methods

●     Compared fossil communities at different times to one another, but tried to eliminate some of the bias that comes along with sampling bias by focusing on four primary taphonomic factors.

●     Depositional  Environments

○     Used faunas from low-energy environments or caves due to the fact that these environments establish more of a complete sample of all of the components of the fossil community and a better representation of the local environments.

●     Agents of Bone  accumulation

○     Mammalian taxa was restricted to certain species densities.

●     Rates of Sedimentation

○     Used environments with rapids rates of sedimentation because it provided the greatest  temporal separation of events.

●     Postdepositional  Disturbances

○     Mixed fossil assemblages were excluded from the data because postdepositional disturbances such as chemical break down in soils and bioturbation can cause mixing of of deposits of different ages and this cause artificial fossil assemblages that do not represent biological communities.  

Results

●     As far as individualistic response goes vegetation, disease, and other interactions may have overridden any direct effects of climate change. This could be the main reason why a lot of the communities are similar to the present day except for the megafauna extinction. Unfortunately this may have been a consequence of human interactions.

Conclusion

●     After gathering extensive amounts of data and finally comparing Pleistocene and Holocene communities, the only true qualitative difference is that the Pleistocene megafauna is extinct. The reality of the matter is that this is due to many changes in the environment and communities themselves. As a result of these changes, many  communities completely reshuffled themselves meaning southern species became more north, as northern species became more southern. They think these drastic environmental changes are the main reason the Pleistocene megafauna became extinct, however, they can not validate their suspicion. What they can validate is that many small animal ecosystems have definitely changed since the Pleistocene.

Comments

●     Interesting topic and research, but as results show, theirs not too much quantitative data.

●     I feel like doing this to see how ancient modern communities are was wrong, and didn’t do much in terms of providing new information used to better the experiment.