NAME: ______DATE: ______BLOCK: _____
Abstract
You will first examine the life table of a large mammal to introduce the concepts of life tables and survivorship curves. You will also look at data that was collected from cemeteries in Massachusetts. You will then collect and compare age-specific mortality data from gravestones in a cemetery in Lancaster. You will construct life tables and graphically illustrate survivorship and mortality rates.
Introduction
A population can be generally defined as a group of interbreeding individuals of the same species occupying a given area at a given time. Populations are dynamic entities that undergo change over time. Populations grow and shrink and the age and gender composition also change through time and in response to changing environmental and social conditions. Population biology is the study of populations and their changes over time. One technique used to study population ecology is the construction of life tables. A life table uses information about age- and gender-specific mortality rates to determine patterns of survivorship and life expectancy. Life tables can be constructed in two ways. The first way is to study a cohort, a group of individuals born at roughly the same time, from birth to death. One such study is Murie’s study, published in 1944, of Dall mountain sheep in Alaska. You will examine and analyze the life table from this cohort study as part of this exercise. Cohort studies are impractical for studying changes in the human population because humans tend to live for a relatively long time. A more practical approach for studying human population ecology is to construct a static life table using data from cemeteries, historical documents, or even obituaries. Using this technique one may sample a given population at a snapshot in time. The data from the life tables can then be used to construct survivorship curves and examine age-specific mortality classes. Survivorship curves generally fall into one of three typical shapes.
Figure 1: Survivorship Curves (www.bioinquiry.vt.edu/bioinquiry/Cheetah/cheetahpaid/cheetahhtmls/popsurvivor.html).
Organisms that exhibit Type I survivorship curves have highest probability of death in old age. Species with Type III survivorship have the greatest probability of death at young ages. In other words, these species suffer very high mortality of eggs and young. Type II survivorship is intermediate between the others and suggests that such species have an even chance of dying at any age.
PART A: DALL MOUNTAIN SHEEP
Look at the life table below for Dall mountain sheep (Ovis dalli).
Figure 2: Life Table for Dall mountain sheep (Ovis dalli). The age of death was recorded for 608 sheep observed in Denali National Park, Alaska, by Olaus Murie in 1944.
Age interval (years) / Number dying during interval / Number surviving during interval / Fraction surviving (lx) / Mortality rate (mx)0-1 / 121 / 608 / 1.000 / 0.199
1-2 / 7 / 487 / 0.801 / 0.014
2-3 / 8 / 480 / 0.789 / 0.017
3-4 / 7 / 472 / 0.776 / 0.015
4-5 / 18 / 455 / 0.764 / 0.039
5-6 / 28 / 447 / 0.734 / 0.063
6-7 / 29 / 419 / 0.688 / 0.069
7-8 / 42 / 390 / 0.640 / 0.108
8-9 / 80 / 348 / 0.571 / 0.230
9-10 / 114 / 268 / 0.439 / 0.426
10-11 / 95 / 154 / 0.252 / 0.671
11-12 / 55 / 59 / 0.096 / 0.933
12-13 / 2 / 4 / 0.006 / 0.500
13-14 / 2 / 2 / 0.003 / 1.000
14-15 / 0 / 0 / 0.000 / ------
*Annual mortality rate, calculated as the ratio of the number dying during age interval to the number surviving at the beginning of that age interval. For example, the mortality rate for the age interval 8-9 years is 80 deaths/348 individuals = 0.230 (23% per year).
Answer the Dall mountain sheep questions on your answer sheet.
PART B: SAMPLE DATA FROM GROTON, MA CEMETERIES
Look at the Figures 3 and 4. This is a sample of data collected from cemeteries in Groton, MA. The data are broken into male vs. female as well as post-1900 (modern) and pre-1820 (historical) for comparison. Mortality calculation example for 67.5 midpoint = (581 – 507)/581 = 0.13 = 13%
Figure 3: Data from two cemeteries in Groton, MA: Post-1900 females and males
Age Class (mid point) / Number surviving females / Mortality for females / Number surviving males / Mortality for males2.5 / 1000 / 0.08 / 1000 / 0.09
7.5 / 924 / 0.01 / 912 / 0.03
12.5 / 914 / 0.02 / 886 / 0.01
17.5 / 898 / 0.03 / 874 / 0.02
22.5 / 869 / 0.03 / 855 / 0.04
27.5 / 843 / 0.03 / 824 / 0.03
32.5 / 816 / 0.02 / 797 / 0.04
37.5 / 797 / 0.04 / 764 / 0.03
42.5 / 769 / 0.03 / 744 / 0.03
47.5 / 745 / 0.03 / 722 / 0.06
52.5 / 720 / 0.04 / 682 / 0.06
57.5 / 686 / 0.05 / 640 / 0.08
62.5 / 652 / 0.11 / 590 / 0.15
67.5 / 581 / 0.13 / 502 / 0.16
72.5 / 507 / 0.19 / 422 / 0.26
77.5 / 413 / 0.30 / 311 / 0.33
82.5 / 287 / 0.40 / 209 / 0.44
87.5 / 173 / 0.52 / 118 / 0.61
92.5 / 83 / 1.00 / 45 / 1.00
Figure 4: Data from two cemeteries in Groton, MA: Pre-1820 females and males
Age Class (mid point) / Number surviving females / Mortality for females / Number surviving males / Mortality for males2.5 / 1000 / 0.23 / 1000 / 0.21
7.5 / 765 / 0.05 / 794 / 0.05
12.5 / 730 / 0.04 / 754 / 0.02
17.5 / 704 / 0.05 / 739 / 0.05
22.5 / 668 / 0.09 / 702 / 0.05
27.5 / 606 / 0.15 / 669 / 0.08
32.5 / 518 / 0.09 / 618 / 0.06
37.5 / 473 / 0.10 / 561 / 0.08
42.5 / 425 / 0.10 / 533 / 0.08
47.5 / 381 / 0.08 / 489 / 0.05
52.5 / 350 / 0.09 / 467 / 0.07
57.5 / 319 / 0.10 / 434 / 0.11
62.5 / 288 / 0.14 / 386 / 0.17
67.5 / 248 / 0.25 / 320 / 0.31
72.5 / 188 / 0.26 / 221 / 0.28
77.5 / 137 / 0.42 / 158 / 0.35
82.5 / 80 / 0.44 / 130 / 0.54
87.5 / 44 / 0.50 / 46 / 0.77
92.5 / 22 / 1.00 / 11 / 1.00
Answer the Groton, MA questions on your answer sheet.
PART C: YOUR TURN TO COLLECT THE DATA IN LANCASTER!
NOTE: It is very important to remember that cemeteries are sacred places. Please do not act disrespectfully or disturb the gravesites or monuments. Be especially considerate if other people are visiting the cemetery.
1. Go to section of the cemetery that your group is studying. You will look at every legible gravestone in the area. Tell your teacher when you have finished but do not move to another area of the cemetery unless you are instructed to do so.
2. One person in the group will be the recorder. His or her job is to record the data called out by the other group members, who are the data collectors.
3. For each deceased person, calculate the age of the person when he or she died. Put a tally mark in the appropriate box in the data sheet based on the year they were born. For example, the tally mark for a person born in 1928 and who died in 1968 would be put in the 40-49 and 1900 box. Put them in the male or female column (based on your best guess given the name).
4. Also, for deaths occurring in the years 1915 – 1922 please put a tally mark in the box of the year that they died.
5. Total each age interval for your group.
6. Turn in your groups’ data to Mrs. Flick.
Answer the Lancaster questions on your answer sheet.
NAME: ______DATE: ______BLOCK: ______
Dall mountain sheep questions
1. Use Excel to construct a survivorship curve by plotting age class midpoint (x-axis) versus number surviving at the beginning of the age interval (y-axis). Attach this curve to your answer packet. Make sure the curve is labeled!
2. What do you know about the way this study was conducted based on what you observe from the data?
3. What don’t you know about this study? List 3 things that you do not know that could affect the data that was collected.
4. What trends or patterns are evident in the data?
5. Explain why these trends may have occurred.
Groton, MA questions
1. Using Excel, make one survivorship graph with 4 curves: post-1900 males, post-1900 females, pre-820 males, and pre-820 females. Attach this graph to your answer packet. Make sure the curves are labeled!
2. Which age intervals show the greatest mortality risk in each population (historical and modern)? Why?
3. What are the gender differences in survivorship in both populations (historical and modern)? Why do you think you see these differences?
4. How do the pre1820 and post 1900 populations compare? Why are there differences?
5. How do the differences in survivorship affect the potential for population increase?
Lancaster questions:
1. Using Excel,
a. construct 4 life tables (one for each: 1800 males, 1800 females, 1900 males and 1900 females)
b. a survivorship graph (with 4 curves comparing male vs. female for the 1800’s and 1900’s ); use the column that is standardized for 100 people
c. a life expectancy graph for each age class (with 4 curves comparing male vs. female for the 1800’s and 1900’s )
d. a death rate graph for each age class (with 4 curves comparing male vs. female for the 1800’s and 1900’s )
e. a graph that shows the number of deaths from 1915-1922 for the population surveyed. Attach the life tables and graphs to your answer packet. Make sure everything is labeled (titles, axes, legends, etc.)!
2. In which year(s) from 1915 to 1922 did you see the most number of deaths? Why?
3. Which age interval shows the greatest death rate in the populations (both 1800s and 1900s)? Why?
4. How does life expectancy correspond to the age classes?
5. Compare the survivorship between the 1800s and 1900s and between males and females). Offer 2 explanations for differences.
6. Compare your Groton, MA and Millersville data for the 1900s and ~1800s. Did you see the same trends? Why or why not?
7. Do the data collected represent an accurate picture of mortality rates in the world human population? Why or why not? What are some of the assumptions? What are some of the limitations and biases of the data collected?
Group members: ______
Age interval (years) / 1800’s males / 1800’s females / 1900’s males / 1900’s females / Years / Number of Deaths in the Year0-9 / 1915
10-19 / 1916
20-29 / 1917
30-39 / 1918
40-49 / 1919
50-59 / 1920
60-69 / 1921
70-79 / 1922
80-89
90-99
100-109
Spring 2013:
Collected data from rows nearest road
Last row collected started with several dark, gray stones (Henry, Barb, Christian HERR)
Spring 2014
Collected data. Start with Philip Mohr and Lizzie Mohr row 14 on Dogwood Lane (between 3 and 4 green sign)
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