## Living Graph: Explore Survivorship curves

This graph is a survivorship curve in standard form. It is generated from the accompanying life table. Explore the effect of changes in the value of ${l}_{x}$ on the shape of the survivorship curve. You can change the values of ${l}_{x}$ by changing the number of individuals alive at age $x\left({N}_{x}\right)$.

1. Try changing the values so that mortality is higher in younger ages. Examine the change in the life table and the change in the survivorship curve.
2. Repeat the exercise, making the number dying approximately constant over the lifespan. Examine the change in the life table and the effect on the survivorship curve.
3. Explain the difference between Type I, Type II, and Type III survivorship curves. What changes in the values of ${N}_{x}$, ${l}_{x}$, and ${d}_{x}$ result in the differences?

The graph plots log number surviving per 1000 from 0 to 3.5, versus age in years from 1 to 14. Log number surviving per 1000: 1, 2.8; 8, 2.7; 10, 2.4; 12, 0.8; 14, 0. All values are estimated.

### TABLE 8.2 - A life table for Dall sheep at Denali National Park, Alaska (data from Murie, 1944)

 AGE INYEARS(X) NUMBER ALIVE AT START OF AGE (Nx) PROPORTION SURVIVING AS FRACTION OF NEWBORN (lx) NUMBER DYING IN AGE INTERVAL (Dx) 0 608 1.000 1 487 0.801 2 480 0.789 3 472 0.776 4 465 0.764 5 447 0.735 6 419 0.689 7 390 0.641 8 348 0.572 9 268 0.441 10 154 0.253 11 59 0.097 12 4 0.0065 13 2 0.003 14 0 0