a cohort life table for marmots
Even when generations overlap, if individuals can be marked early in their life so that they can be recognised subsequently, it is feasible to follow the fate of each year’s cohort separately. It may then be possible to merge the cohorts from the different years of a study to derive a single, ‘typical’ cohort life table. An example is shown in Table 4.2 of females from a population of the yellow‐bellied marmot, Marmota flaviventris. The population was live‐trapped and marmots marked individually from 1962 through to 1993 in the East River Valley of Colorado, USA and it was this that allowed each individual to be assigned, whenever it was caught, to its own cohort.
Table 4.2 A cohort life table for female yellow‐bellied marmots, Marmota flaviventris in Colorado, USA. The columns are explained in the text. Source: After Schwartz et al. (1998).
| Age class (years) x | Number alive at the start of each age class ax | Proportion of original cohort surviving to the start of each age class lx | dx | qx | log ax | log lx | kx | Number of female young produced by each age class Fx | Number of female young produced per surviving individual in each age class mx | Number of female young produced per original individual in each age class lxmx |
|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 773 | 1.000 | 0.457 | 0.457 | 2.888 | 0.00 | 0.26 | 0 | 0.000 | 0.000 |
| 1 | 420 | 0.543 | 0.274 | 0.505 | 2.623 | −0.26 | 0.31 | 0 | 0.000 | 0.000 |
| 2 | 208 | 0.269 | 0.089 | 0.332 | 2.318 | −0.57 | 0.18 | 95 | 0.457 | 0.123 |
| 3 | 139 | 0.180 | 0.043 | 0.237 | 2.143 | −0.75 | 0.12 | 102 | 0.734 | 0.132 |
| 4 | 106 | 0.137 | 0.050 | 0.368 |
