Human Population Ecology: Demography

Introduction

A cemetery is an excellent place to study human demography. Demography is defined as "the study of the characteristics of human populations, such as size, growth, density, distribution and vital statistics". Gravestones record the dates of birth and death, which can be used to dalculate death rates and draw survivorship curves. A survivorship curve is simply a graphical representation of the chance that an individual will survive from birth to a particular age. By comparing survivorship curves for different periods of time, we may look for historical trends in demography over the decades.

Over the last few centuries, advances in health care and large-scale global policial conflict have left rath opposing marks on the demographics of our population. Two major time intervals stand out: before 1950 and after 1950. People who died before 1950 witnessed the industrial revolution, the ravaging effects of polio, as well as World Wars I and II. Following 1950, numerous vaccines and antibiotics were widely used, and with the exception of a few non-global scale wars, this has been an era of relative peace in North America. What do you predict about how the demographics of the human population have changed during these two time periods?

Demographics from local cemeteries can be used, but in order to get a broader scope of life in the US, the world wide web can be used to gather data about birth and death rates all over the country. Many cemeteries now have databases that list all individuals buried there. This is a much faster way than visiting all cemeteries in an area and making assumptions about the overall US population.

Objectives: Once you have completed this lab, you will understand:

1. Some of the basic concepts of population demography
2. how factors such as advances in medicine and environmental protection may have affected human demography over the past 150 years
3. How human demography might chang in the future, based on the current socio-political reality and the presence of incurable diseases (such as AIDS)

Hypotheses

Write your answers to each question below before you start collecting data

1. In general, what are your predictions about death rates of people before or after 1950? Why?

2. In general, what are your predictions about male death rates and female death rates? Would you expect male mortality to be higher? Why?

Methods

Internet connection and cemetery database found at www.interment.net

Collect a wide range of data, though you should categorize data sets into the following four groups: Females who died before 1950, females who died after 1950, males who dided before 1950, and males who died after 1950.

Ideally, data should be collected at random from a variety of places across the US. Given the restrictions on cemetery databases, you'll need to pick larger cemeteries in a couple of different states (a random sample to reflect the entire US population). To ensure that the data you take is random, you may want to just go down a list of names (assuming they're not listed by birth or death dates)

Data Table I

Data Table II: Calculations of Survivorship and Mortality

1. To calculate the # alive, place yout total number of deaths in the first row (0-9) of column B. This is the total number of people in your group upon which death took its toll as they grew older.

2. Subtract the number who died in each age interval (column A) from the number who were "alive" in your sample from the beginning of that age interval. Write this number in the next row in column B. Repeat to fill out column B

3. Calculate the survivorship - for each row in column C, divide the number in column B by the TOTAL you found at the bottom of column A. This gives you the fraction of people that survived to each age interval. By definition, the survivorship of the first age interval equals 1.0 (all living newborns have survived to that point)

Data Analysis & Conclusions

1. Make a graph of survivorship (Y axis) as a function of age group (X axis). Each data set should have its own line (one line for females who died before 1950, one line for females who died after 1950, one line for males who died before 1950, and a line for males who died after 1950. Use Create A Graph or another program to construct your graph. Hand drawn graphs are acceptable as long as they are neat and constructed on graph paper.

2. What is your interpretation of the juvenile (age 0-19) mortality pre and post 1950 for males and for females. List all factors that might account for any differences you see.

3. What is your interpretation of mortality for post-reproductive age adults (50+). List all factors that might account for any differences you see.

4. Compare the survivorship curves of males and females of both pre and post 1950 groups. Do males or females tend to live longer? Are any trends obvious?

5. What shifts in survivorship and mortality curves would you expect if pollution increases causing an increased incidence in environmentally related diseases, such as cancer.

6. What are some limitations to the assumptions you made based on the data you took. How could this experiment be improved?