section21 - MIT Department of Biology 7.014 Introductory...

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MIT Department of Biology 7.014 Introductory Biology, Spring 2005 Recitation Section 21 April 27-28, 2005 Life Tables A. Cohort life table You are studying the life of the common tribble. In a large tribble colony, you mark 1000 newborn tribbles and observe them for the next 5 years. You find the following: Year (age) x # tribbles alive at start of year n x Survivor- ship l x Mortality rate m x Mean # tribbles alive in year L x Average Remaining Life Expectancy e x Average life expectancy for individuals of age x 0 1000 1 900 2 700 3 200 4 50 5 0 1. Derive formulas for and calculate the remaining values in the table, based on the following definitions. l x survivorship in year x = survival of individuals to age x m x mortality rate in year x = proportion of individuals of age x dying by age x+1 L x age units lived in year x = mean # of individuals alive between year x and x+1 e x remaining life expectancy at age x = expectation of further life for individuals of age x 5 L i i = x e = x n x 1
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2. Sketch the survivorship curve for tribbles: 3.
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