Age 0 = cygnets
A life table provides a nice summary of the pattern of survivorship of a population. This pattern of survival rates underlies most age-structured models of populations. When expanded to include age-specific reproductive rates (i.e., fecundity data), the expanded life table can be used to predict the rate of increase of a population and its stable age distribution. Today, we will build an Excel worksheet to perform these calculations for a cohort of trumpeter swans from which we have a sample of ages at death (i.e., Method #1 or Method #3 from the lab notes).
Copy the life table template (Excel spreadsheet) from the course website.
Start Microsoft Excel
The following data were collected from female trumpeter swans banded as cygnets at Red Rocks Lake NWR. Enter these values into the dx column of the life table.
| Age | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 |
| Band Returns | 242 | 12 | 5 | 6 | 5 | 8 | 7 | 8 | 6 | 11 | 10 | 14 | 16 | 11 | 9 | 17 | 11 | 16 | 10 | 12 | 8 | 5 | 3 | 6 | 4 |
Create a life table using the spread sheet and the formulas provided in the lab notes.
Use the following age-specific reproductive rates to complete the extended life table for trumpeter swans at Red Rocks Lakes.
| Age | Female cygnets fledged per female |
| 0 to 5 years | 0 |
| 6 years | 0.18 |
| 7+ years | 0.23 |
Calculate population growth rates R0, lamba, and r.
Is the population increasing, decreasing, or stationary? How can you tell?
Plot the survivorship (lx) and mortality (qx) curves for this population. Note that survivorship should be plotted on a log scale (y-axis). Do these graphs tell you anything that might help you manage this population?
Calculate the finite survival rate for the period from birth to 3-years of age (i.e., age classes 0 to 3). Hint: multiply S0, S1, and S2.
Calculate the stable age distribution (Cx).
Plot the stable age distribution.
Don't forget to save your completed worksheet.
Revised: 10 November 2010