Rose et al. 2001
Flat latitudinal gradient in Paleocene mammal richness suggests decoupling of climate and biodiversity
Rose, P.J., Fox, D.L., Marcot, J., Badgley, C. 2011. Geology 39(2): 163-165.
Blog by Willow Nguy
Authors:
Peter J. Rose
Fox grad student at some point
No further presence since 2011 paper
David L. Fox
Associate Professor in Earth Sciences at U. of Minnesota, Twin Cities
PhD 1999 from U. of Michigan
Uses stable carbon, oxygen, and nitrogen isotopes in sediment and fossils to track changes in the ecology of Pleistocene proboscideans, North American deer populations, and the changes in Miocene Great Plains biomes. Uses stratigraphic data to refine phylogenetic trees (stratocladistics). Also develops paleoclimatic proxies for use in climate-richness gradients.
Jonathon Marcot
Research Asistant Professor in Integrative Biology at U. Illinois Urbana-Champaign
PhD 2003 from U. Chicago
Post doc with Fox
Uses phylogenetic, morphometric, and molecular trends to examine drivers of mammalian diversity.
Catherine Badgley
Professor in Biological Sciences at U. Michigan
PhD 1982 from Yale
Uses taphonomy to correct bias in fossil record populations. Uses stable isotope ratios and faunal change in Pakistan to examine biome change in Miocene. Uses deep time fossil taxonomic data to examine drivers of diversity gradients over latitude and topography.
Featured in Bearded Lady Project
Paper Summary
1. Main Question
There is a negative relationship between latitude and species richness today. Was there also a relationship between latitude and species richness in the Paleocene?
Background: Paleocene (66-56 Ma) occurred after mass extinction that killed the non-avian dinosaurs. Paleocene began the Cenozoic (Age of Mammals). Paleocene mammals are non-analog: they are highly dissimilar to modern mammals and have no clear descendants.
2. Methods
Compiled database of Paleocene mammals broken into two time bins and nine geographic regions spanning 28°lat in western North America. Standardized sampling to combat collection bias. Plotted linear regression of latitude v richness and compared to modern mammals in same region.
3. Results
Latitudinal gradients for both time bins in the Paleocene were roughly zero and significantly different from the modern latitudinal gradient found in that same area.
Why?
· Could it be a sampling bias? No- these areas are very well sampled and have huge collections
· Could Paleocene mammals just all be very similar to each other (same species in each region? No- Statistically, Paleocene mammals in N v S are more different from each other than modern mammals in N v S.
· Could there be a topographic sampling bias? No- when compared to an area with similar topographic range, results are the same.
· Could the ultra warm Paleocene have a shallow latitudinal temperature gradient (hot in tropics just as hot in temperate)? No- Oxygen isotopes (which represent meteoric water and thus environmental temperature) show a latitudinal gradient with a similar slope to the modern, so the difference in temperature between Paleocene tropics and Paleocene temperate was similar to the difference between modern tropics and modern temperate.
4. Conclusions
Maybes!
· Since the Paleocene was all around warmer than today, maybe higher-latitudes had more niche space than today that got ruined by glaciation.
· Since Paleocene mammals are all super weird, geologically new, and we know very little about their ecology, maybe they hadn’t developed a latitudinal gradient yet.
· Since this time period is after a mass extinction, maybe communities were still too unstable to form a latitudinal gradient.
5. Questions/ Comments
a) Since most modern/recognizable lineages came in at the Paleocene-Eocene Thermal Maximum, it was unnecessary to include direct (is ambiguous) descendants. Why didn’t they include bats in their modern latitudinal gradient? This would not have changed the Paleocene gradient, but New World bats drive the modern latitudinal gradient (as we just learned) which would have changed their modern interpretation.
b) In figure one, they extrapolate way past their data. I was always told this was a statistical no-no. While it may not have changed their slopes, it does expose how little a range of latitude was sampled (28°)- this is not a researcher fault, as they used the best material available and more outcrops simply don’t exist.
c) I like that they limited their modern data so that comparison between the two was possible and were very clear not to overstep the boundaries of comparison (comparing general slopes of the oxygen isotopes rather than trying to overinterpret what simply isn’t known).
d) I also liked how systematically they went through each hypothesis. Their investigation was very thorough and they suggested multiple alternatives.
I think even with the incomplete fossil sampling theory you would still see a version of the overall pattern of latitudinal-richness gradient. To me the most likely reason for the difference in this gradient is the lack of temperature gradient at high and low latitudes in the Paleocene. Higher levels of richness were able to thrive at higher latitudes so the pattern is not present. This would also go against the Mid-Domain theory that we talked about since that theory states that either way, the equator should have higher richness.
ReplyDeleteWhen I started reading the results, I also though that the explanation for the non-significant richness gradient is that there were not considerable temperature variability at that time, but then they presented the oxygen isotopes data. Do you think that is not enough to discard similar temperatures along the gradient?. I ask because I´m not a paleontologist and I have no idea on the details of this technique.
DeleteI have to have a nerd moment here. Willow, I love what you wrote about Paleocene mammals being "super weird, geologically new, and we know very little about their ecology". I got hung up on imagining the super cool extinct mammals and couldn't focus on the rest of the paper. Hooray for multituberculates, condylarths, and cimolestans!
ReplyDeleteI'm curious what the Jaccard index values are, haven't heard of them. I find this kind of temporal stuff pretty neat, interested in hearing the discussion.
ReplyDeleteI liked the paper. Thinking about the estimation of species richness at each basin from the fossil record, I wander if it would be possible to use species accumulation curves or other similar method to obtain richness estimates that account for different amounts of samples and provide confidence intervals.
ReplyDeleteI think that the finding of higher beta diversity in the Paleocene than in current mammals is intriguing, I wouldn´t expect that from a biota coming from a mass extinction.
I liked the methodological, step-by-step approach the authors take to determining the potential situations and figuring out which work best given the fossil data. It was a very thorough approach and made it easier to understand their data and the conclusions reached.
ReplyDeleteI enjoyed how in depth the author goes about some of the mathematical approach, this made following along with the paper a little easier. What exactly is Jaccard?
ReplyDeleteI like Alexandria's comment on how the conclusion is kind of going against the theory we discussed in class where the equator would have the highest richness. Maybe it's because the range of latitude sampling is too small, it's not showing us the whole picture.
ReplyDeleteI liked how they analyzed each of the possible mechanisms throughfully. It was clear. However, my lack of familiarity with the isotopes measurements made it difficult for me to understand how and why they analysed that they way they did. I would like to understand that better though.
ReplyDeleteBy the way, I agree with Maria. How mindblowing it is to think of all the crazy extinct animals that were in there!
This is another interesting paper that looks at the latitudinal-richness gradient from the other time perspective using fossils. Anything includes fossils always fascinates me because I believed this is one of the solid pieces of evidence we can get. The contribution of fossil evidence to the modern topography of species dynamics is great even though this paper contradicts with the modern theory of higher richness towards the lower latitude. Also, another cool method is to calibrate the time with evidence using carbon, oxygen and other isotopes are wonderful. This research is the comparison of two modern and past snapshot of life in the past. This means that the species composition and richness of that area is the result of the composition of the species richness of the previous time period. Every setting was different that is why we call this different time period. More sampling is always great but small sample doesn't mean that it is inconclusive. We just have to sample right.
ReplyDelete