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Unformatted text preview: BIS2B Fall 2008 D. R. Strong Lecture 26, Study Guide Life Tables General Patterns of Survivorship. Note the details of the axes in Figure 54.3 and the discussion on page 1170. The figures are plotted semilogarithmically. Recall that a semilog straight line represents the probability of surviving to the next year is about the same over most of the life span These three figures compare the range of survivorship among all organisms. The curves in the middle of figure 54.3 are for three bird species. Note that they are roughly semilog straight lines. This means that agespecific survivorship is roughly constant throughout the life of these organisms. These are called type II survivorship curves and apply to vertebrates with low fecundity. These organisms have roughly the same probability of surviving, and of dying, in each age category. Their agespecific mortality is roughly constant over the course of their lives. Recall the columns in the life table and the definitions of the vital statistics: Age x Nx lx Sx qx 1 BIS2B Fall 2008 D. R. Strong Lecture 26, Study Guide Life Tables Type II survivorship gives roughly semilog straight line plots of Nx and lx. These organisms have intermediate fecundity. Most have parental care, and fairly large individual offspring. Each offspring has a fairly high probability of survival. Consider some grey squirrel survivorship data. In the C4 cell, the formula for l4 is displayed. In the D5 cell, the formula for S5 is displayed. In the E7 cell, the formula for q7 is displayed. The graphs on the following pages alert you to the distinctions between arithmetic and semilog plots of Nx and lx 2 BIS2B Fall 2008 D. R. Strong Lecture 26, Study Guide Life Tables ual A. Note the arithmetic axes. The intervals on the y axis are arithmetic, with eq numbers of units per unit length of the axis. B. Note the semilog axes. a. The line is almost a straight line, thus age specific survivorship is roughly constant. b. Note that we have plotted log10 (Nx) and that the intervals on the y axis are multiplicative. Thus, the number of units in successive intervals is a multiple of the units in the previous interval. 3 BIS2B Fall 2008 D. R. Strong Lecture 26, Study Guide Life Tables l om cause this is lx, the range is 1 to 0. lx and that cross the plot diagonally. C. Note that we are plotting lx v. age, arithmetic axes. The shape of this plot and the arithmetic nature of the y axes are identica to A. above, only the numerical values on the y axis differs fr A. D. Plotting log10(lx) v age, semilog axes. The shape of this plot and the semilog axes are identical to B. above. Only the numerical values on the y axis differs from B....
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