GENERAL ECOLOGY
BIO 340
CEMETERY
CHAPTER 9: Human Demography
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 dada recorded on tombstones.
By collecting information on the year of death for all individuals who died in the same
time period you can produce a graphical representation of their survivorship called a
survivorship curve. For this exercise three time periods will include all individuals born
before 1901, all individuals born between 1901 and 1944, and all individuals born from
1945 to the present.
For the numerous species studied, the curves usually fit one of three general shapes
(Figure 1). Human survivorship typically fits a type 1 curve. However, slight, but
distinct, differences can be seen when survivorship curves from separate human
communities are compared, and when cohorts from different time periods for a single
community are compared, as you will see during this lab.
Page 63
GENERAL ECOLOGY
BIO 340
CEMETERY
OBJECTIVES
In today's lab you will
 Compare and explain the differences in the survivorship curves for at three cohorts
in a community with respect to local or national history.
 Speculate on future changes in demography, based on current community changes.
 Collect age data and calculate survivorship for at three cohorts in a community.
Graph this data to show a survivorship curve for each time period you are studying.
KEY WORDS
Survivorship Curves
Type 1
Type 2
Type 3
Cohort Life Table
Static Life Table
Fecundity
Page 64
GENERAL ECOLOGY
BIO 340
CEMETERY
BACKGROUND
There are several ways to estimate the survival patterns of a population. The most
reliable way to follow a cohort (all individuals within the population that were born in
one time period) and follow it from the time they are born until the time that the last
individual dies. During this study information on the number of individuals that die in
each time period and the number of young that an individual has (fecundity) during
each time period. The definition of a time period is variable and depends on the
characteristics of the species being studied. This data can then be used to construct a
cohort life table. This table can then be used to determine the net reproductive rate
(R), the generation time (T) and per capita rate of increase (r). However, while this
method gives the researcher a large amount if information about the population it is
obtain time consuming and difficult to do.
The second estimator that can be used is done by collecting the death date of the
individuals within a population independent of when they were born. This information
can then be used to construct a static life table. Unlike the cohort life table the static
life table only gives you a snap shot of the survivorship within the population. While R,
T, and r can not be estimated in this type of life table due to a lack of fecundity
information a survivorship curve for the population can be constructed.
A survivorship curve is a graphic version of the survivorship within a population
(Figure 1). These curves usually follow one of three different shapes. A type I
survivorship curve occurs in population in which there is high survivorship in early and
middle age with low survivorship in old age such as seen in humans. Other
populations, such as seen in many birds, have a constant survival rate throughout every
age group in the population. This is called a type II survivorship curve. A type III
survivorship curve is seen in populations that have a low rate of survival in early and
middle age with a high rate of survival in later ages. This curve type can be seen in
such species as insects or fish.
Page 65
GENERAL ECOLOGY
BIO 340
CEMETERY
DIRECTIONS
Field:
1. Divide into groups of 3.
2. Each group responsible for one region of cemetery (90-150 graves). Roads
surround each section of the cemetery.
3. Each person in a group is responsible for collecting data on one specified time
period only: Died before 1900, died 1900-1944, died 1945 – present.
4. Record birth date, death date and sex of all individuals within your cohort.
5. Keep males and females separate for easy collation (males in one column and
females in the other).
6. For each individual calculate the age at death (Table 1).
Laboratory
1. Form new groups with all of the students that collected data for the same death
cohort and summarize the data using Table 2.
2. Summarize the data on Table 3 or in the Excel sheet provided. Note data are
clustered into age classes (first column) of ten year intervals. For the 0-9 age class,
count all of the individuals which died at an age of 9 or less. Continue to record the
number of deaths for each of the age classes. The number of deaths for an age
class is commonly abbreviated as “dx”. When you reach the bottom of the column,
determine the total number of deaths and record this number in the indicated space.
This number should equal the total number of tombstones counted for that cohort.
3. The third column of for survivorship data (nx) or the number of people surveyed that
were alive at the beginning of a given time period. To calculate this, begin by
placing the total number of deaths in the first column in the top cell since everyone
counted was alive at the beginning of the first time period. To determine the number
of for the next box down subtract the number of deaths (d x) that occurred in the first
time period from the previous survival rate. This will tell you the number of people
counted that were alive at the beginning of the second time period. Continue this
process of subtracting the number to the left and one row up to determine the data
for each row of the survivorship column. When you reach the bottom you should
have the total number of 0. (See Table 4 for an example of data in this manner.)
Page 66
GENERAL ECOLOGY
BIO 340
CEMETERY
4. In order to calculate the proportion surviving at the beginning of each time period (l x)
take the number surviving at the beginning of each time period (nx) and divide by the
total from the first column. The values in this column should range from 0 to 1 with 1
for the top row and 0 in the bottom row.
5. Standardize the survivorship data to per 1000 (S1000) to allow you to compare data
form the three decades. Use these equations to make the necessary calculations.
S1000 = (lx)  (1000)
To check your calculations for correctness, the top line should be 1000 and the
bottom line should be zero.
6. In order to make graphing easier calculate the logarithm to the base ten (10) of each
number in the “survivorship per 100” column. Once again to check your
calculations, the number in the top row should be 3 and the bottom line will produce
an error (log 0 is undefined) on your calculator. For this number just put “0”.
7. Using excel, plot your data with the x-axis representing time and the y-axis
representing the log of the proportion of individuals surviving to compare males and
females within your cohort.
Excel Instructions:
a. Highlight the data found in male/female comparison including the labels and
click on the graphing wizard.
b. Choose line graph and the first graph in the second row of choices then click
next 2 times.
c. Label the axis and graph and click next.
d. Choose “as object” and click finish.
8. In order to compare the three different death cohorts studied collect the log (S1000)
data for males and females combined and place it in the chart on sheet 2 of the
excel workbook.
9. Create a graph comparing the survivorship curves for the three different death
cohorts.
Page 67
GENERAL ECOLOGY
BIO 340
CEMETERY
DISCUSSION QUESTIONS
1. Do the curves for the different decades differ from one to another? If so, what might
have caused the differences?
2. How do your graphs compare Figure 2, survivorship curves for Newberry, South
Carolina. Can you explain any differences?
3. How would your data have been altered if your cemetery had closed in 1965 rather
than being opened to the present day?
4. One problem with studying survivorship curves when using birth cohorts is that all
individuals must be followed until they have died. What differences would you
expect to see between the survivorship curves from an 1870’s cohort and a 1940’s
cohort?
5. What would future survivorship curves look like if
a. AIDS continues to increase and no cure is found?
b. Medical advances continue and most diseases and infant mortality are
eliminated?
c. Environmental problems deteriorate and pollution-related disease increases?
6. What assumptions did you need to make in order to develop the survivorship curves
for Mt. Pleasant using the data from this cemetery?
Page 68
GENERAL ECOLOGY
BIO 340
CEMETERY
REFERENCES
Condran, G. and E. Crimmins. 1980. Mortality differentials between rural and urban
areas of states of the northeastern United States 1890-1900. Journal of Historical
Geography 6 (2): 179-202.
Dethlefsen, E.S. and K. Jensen. 1977. Social commentary for the cemetery. Natural
History 86(6) 32-29.
Gwatkin, D.R. and S.K. Brandel. 1982. Life expectancy and population growth in the
third world. Scientific American 246(5): 57-65.
Kuntz, S. 1984. Mortality change in America, 1620-1920. Human Biology 56: 559-582.
Mahler, H. 1980. People. Scientific American 243 (3):67-77.
Molles, M.C. 2002. Ecology: Concepts and Applications Third edition. McGraw-Hill,
Boston.
Page 69
GENERAL ECOLOGY
BIO 340
CEMETERY
Table 1. Data collection sheet - MALES
Time Period _________________________
# of
indiv.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Birth
Yr.
Death
Yr.
Age at
Death
Sex
Page 70
# of
indiv.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Birth
Yr.
Death
Yr.
Age at
Death
Sex
GENERAL ECOLOGY
BIO 340
CEMETERY
Table 2. Data collection sheet - FEMALES
Time Period _________________________
# of
indiv.
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
Birth
Yr.
Death
Yr.
Age at
Death
Sex
Page 71
# of
indiv.
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
Birth
Yr.
Death
Yr.
Age at
Death
Sex
GENERAL ECOLOGY
BIO 340
CEMETERY
TABLE 3. Data compilation for all of the groups of one time period.
Male
AGE
GRP 1 GRP 2 GRP 3 GRP 4 GRP 5 GRP 6 GRP 7 GRP 8 Total
0-9
10_19
20-29
30-39
40-49
50-59
60-69
70-79
80-89
90-99
100-109
110-119
Female
AGE
GRP 1 GRP 2 GRP 3 GRP 4 GRP 5 GRP 6 GRP 7 GRP 8 Total
0-9
10_19
20-29
30-39
40-49
50-59
60-69
70-79
80-89
90-99
100-109
110-119
Page 72
GENERAL ECOLOGY
BIO 340
CEMETERY
TABLE 4: Data calculations for survivorship curve.
TIME PERIOD _________________________________________
Age Class
(Years)
# Deaths
(dx)
# Survivors
(nx)
0-9
10-19
20-29
30-39
40-49
50-59
60-69
70-79
80-89
90-99
100-109
+110
Page 73
Proportion
Surviving (lx)
Survivorship
per 1000
(S1000)
Log (S1000)
GENERAL ECOLOGY
BIO 340
CEMETERY
TABLE 5: Survivorship table summarizing data collected for the 1830’s from a
cemetery in Newberry, South Carolina.
*
Age Class
(Years)
# Deaths
(dx)
# Survivors
(nx)
Proportion
Surviving (lx)
Survivorship
per 1000
(S1000)
Log (S1000)
0-9
8
160
1.000
1000
3.00
10-19
7
152
0.950
950
2.98
20-29
13
145
0.906
906
2.96
30-39
9
132
0.825
825
2.92
40-49
13
123
0.769
769
2.89
50-59
21
110
0.688
688
2.84
60-69
23
89
0.556
556
2.75
70-79
39
66
0.413
413
2.62
80-89
22
27
0.169
169
2.23
90-99
4
5
0.031
31
1.49
100-109
1
1
0.006
6
0.78
+110
0
0
0.000
0
*0
Log (0) is undefined. Consider this value zero.
Page 74