Week 3: Cemetery Demography
Before Lab: Read over the lab and be on time. We‟ll be driving today and
leaving promptly. DRESS APPROPRIATELY!!!
What to Bring to Lab: Bring your lab, a calculator, a hard notebook or
clipboard, pencil (pens can freeze) and wear warm clothes including
boots. We‟ll be outside for a good portion of the lab.
Background:
Demography:
In last week‟s lab we looked at how theoretical populations grow using
models. This week we will focus on demography, which is the study of
biological populations, including human populations. Demography includes
the study of birth rates, death rates, immigration and emigration patterns
which influence population dynamics. Human population dynamics can be
particularly interesting because of how events or trends in human history
affect them. Everyone has heard the term “Baby Boomers” which refers to the
generation that was born after WWII when the economy was strong and
soldiers returning from the war were getting married or were reunited with
their spouses. This socio-political-economic event is observable in records of
human populations via increased birthrate, life expectancy, increased total
population and changes in sex ratios in countries affected by the war. Other
global events that are evident in population data are the flu pandemic of 1918
which killed between 50 and 100 million people in only 18 months. In the US,
this was followed shortly by the Great Depression, which added to the dip in
population.
There are many such events in human history that have impacted populations,
some global and some local. An event that changes a particular population
could be as seemingly insignificant as the closing of a mine in a small West
Virginia town or increasing housing prices in inner city Boston.
Advances in healthcare have also significantly altered demographics in
populations. In the early 1800‟s it is reported that one of every five women
1
died during childbirth and infant mortality was much higher than it is today.
Obviously childbirth is not nearly as fatal today. These changes have been at
least partially attributed to medical breakthroughs such as the discovery of
antibiotics in the 1930‟s and the polio vaccine in the 1950‟s.
Today we will be looking at local demographics and population dynamics by
collecting information from gravestones. From this information we will be able
to identify some basic population data as well as compare characteristics of
age-classes or “cohorts”. For our gravestone study, a cohort will be all
individuals born in the same decade. We will also be using our data to
construct survivorship curves.
We will be investigating the hypothesis that there are differences in
survivorship of cohorts born in the early 1800‟s (1800-1849) compared to
individuals born in the late 1800‟s (1850-1899). We will also be examining the
data to see if sex plays a role in survivorship both as a whole and between the
two time periods.
Survivorship Curves:
Survivorship curves are representations of population mortality over a
lifespan. There are three common forms that these curves can take that
represent different life strategies.
Figure 1: Survivorship Curves Types I, II and III.
I
II
III
Age
Different survivorship curves represent the different breeding strategies of
organisms. It‟s easy to forget that demography includes all biological
populations, not just humans. In Figure 1, line I represents a type I population
that experiences little mortality until old age. Species that follow this type of
curve often have few offspring and provide parental care for the younger age
classes (K strategists). Large animals and ones in the higher trophic levels
such as lions, whales and apes often exhibit type I survivorship. Human
populations also have survivorship curves that appear most like I. However,
2
how would a human survivorship curve differ from I in areas with high infant
mortality?
In contrast, species that exhibit type III survivorship represented in Figure 1
often produce many offspring with little or no parental care in the hope that a
few will survive to adulthood (R strategists). Some examples of these types of
species might include organisms such as octopi, which can lay up to 200,000
eggs. Survival curves can also be calculated for trees which are most often
described by a type III curve. Maple trees for example can drop thousands of
seeds of which only a handful may ever make it to reproductive maturity.
Type II survivorship as seen in Figure 1 is characterized by near constant
mortality over all age classes. Obviously, there are few species that exhibit
strictly one type of survivorship or another but instead are some combination
of type I and III.
Cemeteries:
Cemeteries are interesting in themselves because they reflect social change
and attitudes toward death. Cemeteries prior to the Revolutionary War era,
such as some in Boston, have gravestones decorated with grinning skulls and
cross-bones and stressed man‟s inevitable fate. Cemeteries were muddy and
unkempt, reinforcing this grim message. By the late 1700‟s, death was viewed
more as a release from earthly suffering and white marble, a symbol of purity,
became common for grave markers. They were often shaped like headboards
of beds and the size indicated the age of the deceased.
In the 1830‟s cemeteries began to be run by towns rather than churches and it
became necessary to buy plots. Grave markers became more ornate and for
wealthy families, mausoleums were in vogue. By the late 1800‟s family
memorials had a central marker for the head of the family (an adult male),
with smaller stones around it representing family members. At this time one
out of five women died during childbirth and many children died before the
age of five. Thus, death in the immediate family was fairly frequent. Because
cemeteries held those recently dead individuals, families would often make
weekend excursions to the cemetery and took along picnic lunches. The
atmosphere of cemeteries reflected that social pattern and were groomed for
a park-like effect.
During this century the trend is for husband and wife to have equal and sideby-side headstones stressing the marital bond, rather than the supremacy of
the father.
I‟m sure you don‟t have to be reminded, but cemeteries are places of honor
for those who went before us. Please remember to show respect for the dead
3
and for any other people who may be visiting the cemetery while we gather
data. Please respect the privacy of any people visiting graves by avoiding
those areas.
Methods:
Objectives:
1) Compare and explain differences in the survivorship curves in a
community with respect to sex and historical trends.
2) Speculate on future changes in demography, based on current community
changes.
3) Collect age data and learn how to calculate survivorship using life tables
and create survivorship curves.
Students will be working in pairs and will each be assigned to collect data in a
particular area of the graveyard. Use Table 1 to record individuals. After
sampling is complete, data will be compiled into cohorts, which for this study
will be defined as all of the individuals born in a particular decade. To ensure
that we account for each individual that was born into a particular cohort, we
must be sure that none are still surviving. For this reason, all of the individuals
recorded should have birth years prior to 1900.
To get an adequate sample size, each group will be asked to record year of
birth, death and age of death for as many individuals as they can in a given
amount of time. The sex of the decedent should also be indicated so that we
will be able to see if there are differences between male and female
survivorship. Information should be filled in using Table 1 provided.
Notes: * If a name is ambiguous to sex, omit that individual.
* Also, if only a death date and age at death are given, calculate year of
birth and keep that individual.
* Be sure not to only focus on large tomb stones, since this could be
influenced by wealth and quality of healthcare.
* Do your best to read the grave stones. If they are illegible, you may
want to use crayons and make a rubbing if they are available.
Data Analysis:
After Class:
1) For each individual you recorded in the cemetery, calculate the age at
death to complete Table 1. You will be putting this information into an
Excel spreadsheet and emailing it to your TA. You will also be emailing
a summarized version of your data. (The tables you have to fill in and
return electronically will be sent to your email this week)
4
2) The summary of your data will be made by grouping each of your
individuals into cohorts by decade and by sex (1 per pair). Cohorts as
previously stated will be defined as individuals born in the same
decade. Note that the data will be clustered into age classes of ten year
intervals. For the 0-9 age class, count all of the individuals who died at
an age of 9 or less. For the 10-19 year age class count all of the
individuals who died at an age of 10 to 19 and so on.
3) To summarize the data for the whole class, your extremely talented
TA‟s will use your emailed data to compile the results and then
distribute that data to you for use in your lab report.
In class:
1) You will be making life tables based on data supplied by your TA. You
should make one for men and one for women using Table 3 and the
following instructions as a guide. Numerical definitions can also be
found in your Primer of Ecology textbook in Chapter 3.
2) The second column is the first you need to fill in (dx). This represents
the number of individuals that died at the age indicated in column one.
The third column is for the number of individuals surviving at each age
step (Sx) and indicates the number of individuals remaining in the
population. The calculations of these data are cumulative. Begin by
placing a zero in the lowest box of the column. To determine the
number for the next box up, add to the zero the number of deaths (dx)
that appears in the column to the left and one row up. Continue this
process of adding on the number to the left and one row up to
determine the data for each row of the survivorship column. When you
reach the top you should have the total number of individuals that you
originally counted.
3) Now calculate the proportional survivorship by dividing each number
in the Sx column by the total number of individuals you counted of that
sex and enter it into the next column. This should be the proportional
survivorship. (The first box should equal 1 and the last 0) This will allow
you to compare data between sexes even if you did not count the same
number of individuals in each.
4) The next column is Log Survivorship and is self-explanatory. Simply
take the natural log of your proportional survivorship.
5) The last column, probability of survival gx, should then be filled in. This
column represents the probability that an individual will make it to that
age class.
5
6) Make your own survivorship curves with age classes and proportional
survivorship.
Assignment.
This lab will form the basis of a long lab report. You will be expected to
calculate and compare survivorship curves for males and females in the early
and late 18th century. Your results will be presented in a formal lab report.
We will discuss the format of your report in lab and you will be able to
download detailed instructions on the format of the lab report.
Your report will be due in class on Wednesday, February 20. This schedule is
also posted on the course WebCT site under „Schedule‟.
6