Human Demography and Disease Ecology
Summary
For this lab, you will estimate static life tables for historic and contemporary human populations
and discuss the role of diseases and disease ecology on population dynamics. You will gather
mortality data for a historic human population from Cedar Grove Cemetery located on/near
campus and you will gather data from obituaries published in past issues of the South Bend
Tribune for a contemporary human population. You also will be comparing two U.S.
populations with AIDS to see if there are differences in mortality trends. You will 1) submit
several graphs showing various life history characteristics, including mortality, survivorship, and
population age-structures for several different population groups and 2) think critically about and
synthesize the results of this work by answering several questions.
Required Reading (you will need to read these to answer results and discussion questions)
Textbook: Pages 180-182, 185-201.
Literature: Pimentel, D., M. Tort, L. D’Anna, A. Krawic, J. Berger, J. Rossman, F. Mugo, N.
Doon, M. Shriberg, E. Howard, S. Lee, and J. Talbot. 1998. Ecology of
increasing disease. BioScience 48(10): 817-826.
Supplemental Website Information
Websites:
http://www.cdc.gov
http://www.cdc.gov/ncidod/index.htm
http://www.cdc.gov/mmwr/
http://www.cdc.gov/ncidod/dvbid/index.htm
Introduction
As the United States has progressed through the industrial
revolution over the last 150 years, changes in the life-styles of
citizens have been reflected in their age at death. Factors such as
diseases and accidents have changed in their relative impacts. One
way to study these changes in human demographic patterns is to
visit a local cemetery and collect data recorded on tombstones.
By collecting information on the year of death for all individuals of
the same age class (a cohort) you can produce a graphical
representation of their survivorship. For this exercise, a cohort (or
age-specific) life table records population characteristics for an
equal-aged group of organisms followed from birth to death. For
most organisms, this sort of data is difficult to obtain, so most life
tables are static (or time-specific) life tables, constructed from
current (i.e., time-specific) mortality rates by age. In the rare cases
Figure 1: Three types of
survivorship curves: Type 1
shows low initial mortality and
many individuals living to old
age. Type 2 shows a steady death
rate. Type 3 shows high initial
mortality with few individuals
living to old age.
1
in which neither population size nor mortality rates change with time, all we need for a timespecific table are the sizes of different classes.
For the numerous species studied, the curves usually fit one of three general shapes (Figure 1).
Human survivorship typically fits a type 1 curve. Especially interesting though, is that slight, but
distinct, differences can be seen when curves from separate communities are compared, or when
cohorts from different decades for a single community are compared, as you will do during this
lab.
Another important aspect of creating life tables is their application to disease ecology in tracking
the emergence, spread, and effect of diseases and epidemics. For example, ecological and
demographic changes may create new or more favorable habitats for disease vectors, such as the
potential changes caused by global climate change.
Objectives
1. To understand survivorship curve and life table.
2. To construct life tables and compare population characteristics for human populations.
3. To understand the importance of demography in disease ecology.
Materials and Methods
Field Procedure
Cedar Grove Cemetery:
1. Divide up into four groups and examine
tombstones located in cemetery sections A,
B, C and D. Try to assign an area of the
F
D
B
cemetery for each member of your group
to look at; we want to avoid double
counting tombstones!
2. Collect data only from individuals who died
in or before 1920.
N
3. If you cannot discern whether the person
E
C
A
was male or female, omit the datum.
4. If only initials are given, assume the
individual was a male.
Angela Boulevard
5. Figure out the age of death. Record the individual
on Data Sheet 1 (Historic Males) or Data Sheet 2 (Historic Females) depending on the sex.
6. Record 25 per sex, per student.
Lab Procedure
1. Divide up into four groups and collect data for the contemporary human population from the
available newspapers.
2
2. Figure out the age of death. Record the individual on Data Sheet 3 (Contemporary Males)
and Data Sheet 4 (Contemporary Females), record the same sort of data for the contemporary
human population from the available newspapers.
3. Record 25 individuals per sex, per student.
Spreadsheets
1. Because birth and death statistics in human populations are expressed as events per thousand
people, each group will standardize each population to a size of 1000. This number will go
in the column dx, or the age-specific death rate, which calculates the normalized number of
people dying per age group (total population counts multiplied by the normalizing factor,
which is 1000 divided by your sample size). This is an important step since the entire life
table can be filled out based on this number. To standardize:
dx = (# deaths in each age group / total # of deaths of ALL age groups) * 1000
2. Each member of the class must have the data to calculate the age specific death rates for
each population before leaving lab. Using the life table spreadsheet as a guide, fill in a
spreadsheet for each population (historic males, historic females, contemporary males, and
contemporary females). Since we are tracking the deaths of 1000 people in each population,
there are 1000 individuals in the population (i.e. n0 = 1000) at the beginning of the age
interval (time 0). This is the number of individuals that started out at age zero (although they
did so at different times).
3. Use only one sheet because you will need access to all the information. Make sure to label
the appropriate columns so that you can tell which one is which on your graphs. Please use
the sample spreadsheet given to you by your T.A. as a template for your own spreadsheets
(you will have to make all the necessary calculations though).
Formulae for Spreadsheet
x
=
age at beginning of interval
nx
=
number of survivors at start of age interval x (nx = n x-1 - d x –1)
lx
=
proportion of humans surviving to start of age interval x (lx = nx / no)
mx
=
average number of offspring per individual during the age interval
lxmx =
multiplication of lx and mx, summing this column gives you Ro (the net
reproductive rate per individual)
dx
=
number dying during age interval x to x + 1
qx
=
proportion of group dying during age interval (use for mortality curve)
x to x + 1 (qx = dx / nx)
Lx
=
average number of individuals alive during age interval
x to x + 1 (Lx = (nx + n x + 1)/2)
=
“stationary age distribution” which is the age distribution the population
would have if it were constant (i.e. births = deaths).
Tx
=
Total years to be lived by individuals of age x in the population. The sum
of Lx (e.g. T80 = L80 + L85 + L90 + L95 + L100)
ex
=
mean expectation of remaining years of life for individuals alive at start of
age x
=
5 Tx / nx (the constant, 5, appears in the term because our age interval is 5
years)
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Graphs
When you have completed the life tables, make the following graphs. Please be consistent in
your labeling and symbol use for each population on the graphs! Also include a brief figure
caption numbering and explaining the contents of the figures and any trends seen.
1. On one graph (Figure 1), graph survivorship curves (nx on the y axis against age (x) on the x
axis) for the four sets of data.
2. On one graph (Figure 2), graph mortality curves (qx against x) for the four sets of data.
3. Graph two age-structured histograms [x against (Lx / Σ Lx)]: one for the Historic Population
(Figure 3) and one for the Contemporary Population (Figure 4). In both graphs, place the
males on the LEFT side and females on the RIGHT. For histogram instructions, refer to
Appendix A. Follow the directions precisely.
4. Graph mortality curves comparing the U.S. Population that died of AIDS in 1999-2000 from
the U.S. Population that died of AIDS in 1989-1990. For instructions to acquire this data,
refer to Appendix B. Follow the directions precisely. You will have to create a separate
spreadsheet to enter in this data (use the sample spreadsheet as a guide). NOTE: These
mortality curves are different than previously done and than what you’ve learned in class! We
will just be graphing dx against x (rather than qx) because we are assuming that the population
is stable.
Results
Turn in the following on separate pages:
 Tables 1-6 - the spreadsheets of Historic Males (Table 1), Historic Females (Table 2),
Contemporary Males (Table 3), Contemporary Females (Table 4), U.S. Population that
died of AIDS in 1999-2000 (Table 5), and U.S. Population that died of AIDS in 19891990 (Table 6)
 Figure 1 – a figure showing the survivorship curves for all 4 SB Populations
 Figure 2 – a figure showing the mortality curves for all 4 SB Populations
 Figure 3 – age-structured histogram for the Historic Population
 Figure 4 – age-structured histogram for the Contemporary Population
 Figure 5 – a histogram showing the mortality curves for two U.S. Populations with AIDS
Answer these questions in 1 page or less, referencing figures where appropriate (12 pt. font, 1
inch margins, double-spaced):
1. Do the survivorship curves, mortality curves, and population ages structures for the different
populations differ from one another? Do they differ between the sexes?
2. What are the reproductive rates (R0) for the contemporary and historic populations? Why are
only female offspring included in this estimate? How do the net reproductive rates compare?
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3. Calculate the dependency ratio (ratio of the population that is age > 65 [i.e., drawing social
security] to the population that is 15-65 years [i.e., wage earners contributing to social
security]. HINT: use a living population. Which working population would have to pay a
greater percentage of its income to support the current group of people on social security
(historic or contemporary)?
4. In Figure 5, you are comparing the mortality curves of the U.S. Population that died of AIDS
in 1989-1990 to the U.S. Population that died of AIDS in 1999-2000.
Discussion
Now that you have analyzed your data and described the trends, briefly explain the following
points in 2 pages or less (12 pt. font, 1 inch margins, double-spaced):
 Explain what could have caused any differences that you saw in the results (between sexes,
populations, net reproductive rate, AIDS populations). Speculate on mechanisms that could
be driving these differences.
 Why did you see the results that you got when calculating dependency ratios?
 If the historic and modern populations were both actually contemporary (e.g., in different
countries) and each had access to similar health care, which population would grow more
quickly? Why?
 According to Pimentel et al. (1998), is there a relationship between environmental
degradation and prevalence of disease? If so, what is this relationship? Do you think human
population growth will continue to increase, or will diseases and pollution limit our growth?
 What type of assumptions did you (and all ecologists) need to make in order to develop the
survivorship curves?
Checklist for What to Turn in
Your lab report should include:
elbaT ‫ٱ‬s 1-6 - Historic Males and Females, Contemporary Males and Females, U.S. Population
that died of AIDS in 1999-2000, U.S. Population that died of AIDS in 1989-1990 spreadsheets
1 erugiF ‫ٱ‬- Graph of Survivorship Curves for Historic and Contemporary Males and Females
2 erugiF ‫ –ٱ‬Graph of Mortality Curves for Historic and Contemporary Males and Females
3 erugiF ‫ –ٱ‬Age-structured Histogram of Historic Population
‫ ٱ‬Figure 4 – Age-structured Histogram of Contemporary Population
5 erugiF ‫ –ٱ‬Graph of Mortality Curves for two U.S. Populations with AIDS
stluseR morf snoitseuQ ot srewsnA ‫ٱ‬Section
‫ ٱ‬Discussion Section
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Appendix A - How to Make the Age-Structure Histogram (age against (Lx
/Lx)*100)
1. You need 5 columns for x (age) and (Lx / Lx)*100) for Historic Male, Historic Female,
Contemporary Male, and Contemporary Female. Make sure that the data columns have these
titles. Make the male numbers for (Lx / Lx)*100) negative so they can be plotted against
females.
2. Select the Historic Male and Historic Female columns (or contemporary male and female
columns), but DO NOT select the x (age) column. Remember that noncontiguous columns
can be selected by holding down the command key.
3. Select the Chart Wizard, and in step 1 choose BAR and the first sub-type (top left).
4. In step 2 you need to ensure that the proper data are selected. Under DATA RANGE, the
Historical Male and Historical Female data and their column labels should be selected.
Under SERIES, the SERIES box should show Historic Male and Historic Female. Select the
"age" column for the CATEGORY (x) AXIS LABEL. This is a bit counterintuitive, but
excel has rotated the graph 90 degrees so the X-AXIS is the vertical axis (labeled with age)
and the Y-AXIS is the horizontal axis (labeled with percent of population in an age class
(Lx / Lx)*100).
5. In step 3 put in the CHART TITLE and titles for the X and Y axes. Don’t include gridlines,
but do show the legend. The y-axis label should include the summation sign (). Mac users
can type option-w. PC users should type a lower case J (j). The j is summation sign in the
‘WP Math Extended A’ font.
So, if I wanted the y-axis (horizontal axis) to have the label:
Percent of Population ((Lx / Lx)*100)
I would enter the following into the space for y-axis label:
Percent of Population ((Lx/jLx)*100)
The summation sign (in place of j) and the subscripts will be added later (step 9)
6. Finish with the Chart Wizard.
7. Double-click on any of the data bars on the graph. The FORMAT DATA SERIES window
should appear. Under OPTIONS in the FORMAT DATA SERIES window, choose
OVERLAP = 100 and GAP WIDTH = 0. This aligns the male and female data bars.
8. Double-click on the horizontal (y) axis, and the FORMAT AXIS window should appear.
Select SCALE and put in the appropriate minimum and maximum values so that differences
between populations in your histograms are evident.
9. For the subscripts in the horizontal (Y) axis, select the letter to have the subscript (e.g., x in
Lx), and choose from the pull-down menus FORMAT/SELECTED AXIS TITLE and toggle
SUBSCRIPT. To change the j into a , select the j in the axis label and choose
FORMAT/SELECTED AXIS TITLE and select the font WP MATH EXTENDED A.
10. Double-click on the male portion of the bar. The FORMAT DATA SERIES window should
appear. Choose PATTERNS and under AREA choose white. Do the same for the female
portion of the bar, except make it gray.
6
Appendix A (continued) - Example of Histogram:
7
Appendix B – Instructions to Acquire Data for Figure 6 comparing the U.S.
Population that died of AIDS in 1989-1990 to the U.S. Population that died of
AIDS in 1999-2000
1. To get the data to create the graph, follow the instructions below completely (there are
some sections on these web pages that you will not select or use).
2. Go to http://wonder.cdc.gov. Click on the link Mortality – Underlying Causes of Death
(under the Chronic Diseases Heading).
3. To get data for the U.S. Population that died of AIDS in 1999-2000, click on the
Mortality for 1999-2001. Under Number 1, select “United States”, “All Race”, “All
Gender”, and Age Ranges “Under 1 day” to “85 Years and older”.
4. Under Number 3, click on “Keyword Search of ICD” and type in AIDS in the window.
Click on the “Keyword Search”.
5. Highlight the first selection that will appear on the right (B20 – Human
Immunodeficiency Virus (HIV) Disease resulting in infectious and parasitic disease).
6. Click on “Move Individual Codes”, and they will appear in the boxes on the left.
7. Go to 4 and select “Summarize Data by Age”.
8. Click on “Send” at the bottom of the page and a new window will appear with your data.
9. Record the death counts (Columns 1 and 2 on the web page) on a separate spreadsheet,
using the sample spreadsheet as a guide.
10. To get the data for the U.S. Population that died of AIDS in 1989-1990, click on the
Mortality for 1979-1998. Under Number 1, select “United States”, “All Race”, “All
Gender”, Age Ranges “Under 1 day” to “85 Years and older”, and Years from “1989” to
“1990”.
11. Under Number 3, click on “Keyword of ICD” and type in AIDS in the keyword search.
Click on the “Keyword Search”.
12. Highlight the first selection that will appear on the right (042 – Human
Immunodeficiency Virus (HIV) disease).
13. Click on “Move Individual Codes,” and they will appear in the boxes on the left.
14. Go to 4 and select “Summarize Data by Age”. Click on “Send” and a new window will
appear with your data.
15. Record the death counts (Columns 1 and 2 on the web page) on a separate spreadsheet,
using the sample spreadsheet as a guide.
16. Graph mortality curves comparing the U.S. Population that died of AIDS in 1989-1990 to
the U.S. Population that died of AIDS in 1999-2000.
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Historic Males
Data Sheet 1
Age at death data for historic population
______________________________________________________________________________
Name: _______________________
Date: _________________
Group members compiling data: _______________________________
Age at Death (years)
0-4.99
5-9.99
10-14.99
15-19.99
20-24.99
25-29.99
30-34.99
35-39.99
40-44.99
45-49.99
50-54.99
55-59.99
60-64.99
65-69.99
70-74.99
75-79.99
80-84.99
85-89.99
90-94.99
95-99.99
Greater than 100
Individual Data (Males)
Pooled Class Data (Males)
TOTALS:
9
Historic Females
Data Sheet 2
Age at death data for historic population
______________________________________________________________________________
Name: _______________________
Date: _________________
Group members compiling data: _______________________________
Age at Death (years)
0-4.99
5-9.99
10-14.99
15-19.99
20-24.99
25-29.99
30-34.99
35-39.99
40-44.99
45-49.99
50-54.99
55-59.99
60-64.99
65-69.99
70-74.99
75-79.99
80-84.99
85-89.99
90-94.99
95-99.99
Greater than 100
Individual Data (Females)
Pooled Class Data (Females)
TOTALS:
10
Contemporary Males
Data Sheet 3
Age at death data for contemporary population
______________________________________________________________________________
Name: _______________________
Date: _________________
Group members compiling data: _______________________________
Age at Death (years)
0-4.99
5-9.99
10-14.99
15-19.99
20-24.99
25-29.99
30-34.99
35-39.99
40-44.99
45-49.99
50-54.99
55-59.99
60-64.99
65-69.99
70-74.99
75-79.99
80-84.99
85-89.99
90-94.99
95-99.99
Greater than 100
Individual Data (Males)
Pooled Class Data (Males)
TOTALS:
11
Contemporary Females
Data Sheet 4
Age at death data for contemporary population
______________________________________________________________________________
Name: _______________________
Date: _________________
Group members compiling data: _______________________________
Age at Death (years)
0-4.99
5-9.99
10-14.99
15-19.99
20-24.99
25-29.99
30-34.99
35-39.99
40-44.99
45-49.99
50-54.99
55-59.99
60-64.99
65-69.99
70-74.99
75-79.99
80-84.99
85-89.99
90-94.99
95-99.99
Greater than 100
Individual Data (Females)
Pooled Class Data Females)
TOTALS:
12