Calculating Extinction and Origination Rates - Mass Extinction or Biodiversity Crisis?
Summary
In this activity, students will learn how to calculate extinction and origination rates using 'boundary crossing' taxa, and then use published data (Stigall, 2010) to assess how these rates changed across the Late Devonian Mass Extinction. Once completed they will be able to discuss whether this event was a 'Mass Extinction' (increased extinction rate) or a 'Biodiversity Crisis' (decreased speciation rate).
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Context
Audience
I use this activity in my 200-level Earth History course, which is required for majors and my 400-level paleobiology course, which is an elective.
Skills and concepts that students must have mastered
Students should have an understanding of Phanerozoic diversity (Sepkoski Curve) and that mass extinctions have occurred in the past. Students should be able to 'plug and chug' decimal fractions into a formula.
How the activity is situated in the course
I use this in my Earth History course when discussing the Mid-Paleozoic. I use the exercise to help us understand how origination and extinction set total diversity. In my paleobiology course I use it as an introduction to calculating extinction and origination rates, then use the PBDB to calculate extinction and origination rates for clades through the Phanerozoic (a separate exercise).
Goals
Content/concepts goals for this activity
- Students can describe how speciation and extinction rates interact to produce standing diversity.
- Students can explain how changing extinction and origination rates led to the Late Devonian 'Mass Extinction'.
Higher order thinking skills goals for this activity
- Students can develop at least two hypotheses for why diversity decreased across the Late Devonian (increased rate of extinction OR decreased rate of origination).
Other skills goals for this activity
- Students need to create and interpret plots of extinction and origination rates.
Description and Teaching Materials
This lesson begins by discussing the Big 5 mass extinctions and how these are times when the rate of extinction is elevated beyond 'background extinction'. We then discuss how to calculate the rates of extinction and origination fairly using the boundary crosser method. Finally, we use data from Stigall, 2010 to show that the Late Devonian Mass Extinction is primarily driven by a decrease in speciation rates, not an increase in extinction rates.
Detailed instructions and figures are in the 'Extinction and Speciation Rates - Lesson Plan' file. The data from Stigall, 2010 can be found in 'Late Devonian Mass Extinction Activity'. The data is in the form of a spreadsheet. I usually print the sheet and have students work on paper, but I have also done the activity in-person using Google Sheets/Excel and online.
I've included the resources here as Google Drive links and as Word/Excel files.
Extinction and Speciation Rates - Lesson Plan (Microsoft Word 2007 (.docx) 693kB Nov9 22) (Google Docs version)
Late Devonian Mass Extinction Activity (Excel 2007 (.xlsx) 71kB Nov9 22) (Google Sheets version)
Teaching Notes and Tips
Some things to look out for:
- Students can get confused between the terms Psur/Pevo (the proportion of surviving and originating taxa) and p-hat (the rate or extinction).
- Some students calculate Psur/Pevo and put that in the column for p or q. They need to use the whole equation.
- d is diversification, p-q
Assessment
At the end of the activity I use an exit slip (if time allows) to assess their understanding of how extinction and origination rates interact.
This question is repeated on my exam as a short-answer question.
References and Resources
- Stigall, Alycia L. "Invasive species and biodiversity crises: testing the link in the Late Devonian."PLoS One 5.12 (2010): e15584.
- Stigall, Alycia L. "Speciation collapse and invasive species dynamics during the Late Devonian "Mass Extinction"."GSA Today 22.1 (2012): 4-9.
- Principles of Paleontology, 3rd Edition (Michael Foote and Arnold I. Miller, 2007, W.H. Freeman and Co., 354 pp.)