I'm not sure what a complete answer would look like to this question, but since I know how to find the data for the University of Illinois at Urbana-Champaign, I'll answer for that school. Hopefully others will be able to answer in other ways or from other schools. The data I used is publicly available at http://dmi.illinois.edu/cp/, bless their hearts. Disclaimer: I worked there teaching calculus and advising undergraduates for three excellent years before moving on to a full-time teaching role at another school.
Summary of What Follows
I use publicly-available employment data to estimate the amount of math research that was done at University of Illinois from 2004-2013. Then I use publicly-available course data to estimate the amount of calculus taught on the same time period. If you don't care about the details of how my estimates happened, you can skip to the results.
The results section suggests that there has been a massive increase in calculus taught with no corresponding increase in math research done. The conclusion, which is essentially from my personal experience, is that an increased calculus population is much more likely to drive up class sizes and academic professional employment rather than lead to the hiring of many new math researchers.
An Estimate of the Amount of Math Research Done at UIUC, 2004-2014
I'll start with this chart of Full-Time Equivalent Employees of UIUC's Math Department, 2004-2014:
'13-14 '12-13 '11-12 '10-11 '09-10 '08-09 '07-08 '06-07 '05-06 '04-05
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Tenure Track 65.25 62.25 62.17 64.67 62.78 65.73 70.74 67.87 66.67 65.67
Visiting Faculty 9.00 9.75 8.50 4.00 3.00 2.00 7.00 6.50 5.00 9.25
Other Instructors 21.12 20.20 12.06 16.42 18.18 19.98 14.53 20.00 17.97 22.52
Academic Professionals 17.10 15.60 14.35 10.85 10.35 10.35 9.85 9.55 7.80 6.05
Teaching Assistants 69.56 66.88 64.60 64.80 69.69 66.55 63.79 65.30 61.52 60.07
Research Assistants 5.75 8.25 8.37 6.96 8.36 7.00 9.50 4.50 2.83 6.35
Civil Service Staff 10.75 9.75 10.19 9.75 9.75 9.75 9.75 9.75 9.75 9.25
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**Total** 199.53 193.68 180.23 177.94 182.11 181.86 185.16 183.47 171.91 179.16
The units here are "full-time equivalents." So a part-time employee working 28 hours per week would count as 0.7 FTE's toward their row. What you should notice is that there is a nearly-constant amount of math research being done, as best we can tell from this data: besides one outlier year involving a retirement policy, there have always been between 74 and 82 full-time-equivalents of math researchers employed by the department. I added the tenure-track faculty, visiting faculty, and research assistants to find an estimate of "math research done":
'13-14 '12-13 '11-12 '10-11 '09-10 '08-09 '07-08 '06-07 '05-06 '04-05
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Tenure+Visit+Research 80 80.25 79.04 75.63 74.14 74.73 87.24 78.87 74.5 81.27
An estimate of the amount of calculus taken at UIUC, 2004-2013
We can start with the number of Instructional Units taught by the math department. An instructional Unit is awarded when a student completes one credit hour of a math course.
'13-14 '12-13 '11-12 '10-11 '09-10 '08-09 '07-08 '06-07 '05-06 '04-05
100 level 8119 9104 8751 9556 9940 10004 10901 12477 11695
200 level 46530 44647 41731 39170 38897 32870 29437 28964 25211
300 level 1486 1213 1192 1204 1234 3438 6363 6360 7024
400 level 13195 12165 10730 10648 9848 9360 9481 9043 9860
500+ level 5086 5138 5089 5055 4906 4806 5193 5591 5740
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Total 74416 72267 67493 65633 64825 60478 61375 62435 59530
We are lucky in that the vast majority of the 200-level classes are calculus classes (exceptions are other "service courses" like Discrete Math, beginning Linear Algebra, and Differential Equations, which presumably fit under the same question anyway), and all of the calculus classes are 200-level, so the publicly available data is pretty good for our purposes: the row of 200-level data is almost exactly the "amount of calculus taught," in units of credit hours.
Results
Using the above methods, I arrive at the following estimates (no '13-14 data for courses yet, so drop it):
'12-13 '11-12 '10-11 '09-10 '08-09 '07-08 '06-07 '05-06 '04-05
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Math Research (in FTEs) 80.25 79.04 75.63 74.14 74.73 87.24 78.87 74.5 81.27
Calculus Taught (in credit hours) 46530 44647 41731 39170 38897 32870 29437 28964 25211
Sorry about all the data being in reverse order; that's how it is on their website. At least my chart is in the correct order:
Conclusion
This is not a complete answer to the question of course, but at least for one research institution for the last ten years, you can see that there has been a massive increase (nearly doubling) in the amount of calculus taught over the past ten years, with no corresponding increase in the amount of employment for math researchers. This suggests that at least at this school, a possible future crash in the amount of calculus taught would also not have a corresponding disastrous impact on the amount of math research completed at the school.
Instead, calculus increases (at this school) were mostly handled by increased class sizes and by increases in the "Academic Professional" categories -- employees who are wonderful usually-full-time employees who are teaching calculus part-time and doing other things (advising, recruiting, careers, directing initiative) but not doing math research.
I welcome and wish for criticism on my methods and conclusions!
