untitled

1 The sample is an unbiased representation of the living age distribution in the

first case or of the true frequency of ages at death in the second. The exercise would

have to control the usual biases implicit in hunting activities if the sample of the

living age distribution were obtained by shooting. One would be unlikely to use

a sample obtained by sporting hunters, for example. The first age class is usually

underestimated in a picked-up sample of ages at death because the skulls of young

animals disintegrate much faster than do those of adults, thereby significantly bias-

ing the table.

2 Age-specific fecundity and mortality must have remained essentially unchanged for

a couple of generations.

3 Whether the sample is of the living population or of the ages at death, the popu-

lation from which it came must have a rate of increase very close to zero, or else the

data must be transformed to accommodate the observed rate of population change

over the past two generations. Major fluctuations in recent rates of growth invalidate

virtually all such indirect methods. This can limit the usefulness of such exercises

in wildlife management.

We restrict the following discussion to females for simplicity, but the points made

apply also to the male segment of the population.

Remember that lxis survivorship to age x, mxis production of daughters per female

at age x, and ris the exponential rate at which the population increases. Then:

∑lxmxe−rx= 1

POPULATION GROWTH 87

Mortality Mortality Mortality

Age frequency corrected Mortality Survivorship rate

(x)(fx)(fdx)(dx)(lx)(qx)

0 – 485 0.485 1.000 0.485

1 – 129 0.129 0.515 0.250

2 2 4 0.004 0.387 0.010

3 5 11 0.011 0.383 0.029

4 5 11 0.011 0.372 0.030

5 6 13 0.013 0.361 0.036

6 18 38 0.038 0.348 0.109

7 17 36 0.036 0.310 0.116

8 20 42 0.042 0.274 0.153

9 17 36 0.036 0.232 0.155

10 15 32 0.032 0.196 0.163

11 16 34 0.034 0.164 0.207

12 18 38 0.038 0.130 0.292

13 15 32 0.032 0.092 0.348

14 14 29 0.029 0.060 0.483

15 8 17 0.017 0.031 0.548

16 5 10 0.010 0.014 0.714

17 1 2 0.002 0.004 0.500

18 0 0 0.000 0.002 0.000

(^19) _ (^1) _ 2 0.002 0.002 1.000
183 1001 1.001
Table 6.5Construction
of a life table from
a pick-up sample of
African buffalo skulls.
The table is not
corrected for rate
of increase.

6.7 Relationship between parameters