because we know that the average tenure of males in a group is 26.5 months,
varying from just a few days to 74 months. We can assume that each month there is
a 4 % chance of being replaced, so that after the average tenure time passes most
males will have been replaced. (The DT must be set at one for this to work, if DT is
set at 0.5, the 0.96 will have to be replaced by 0.98 so that the same chance is
encountered).
A second unknown is whether the new male (should he win his dominance
challenge) is himself infanticidal. To determine the likelihood that a male commits
infanticide, we specify another random number generator in much the same way,
only this time creating a component called “Pct Infanticidal” in which we can
actually vary the percentage of males in the population who will exhibit this trait. A
converter called “Is_new_male_infanticidal?” uses the random number generator
and the percentage specified to determine the answer to this question. Its value is
Is new male infanticidal ¼ IF Random # Gen 2 <¼ Pct Infanticidal THEN 1
ELSE 0},
ð14:3Þ
such that if 40 % are infanticidal (Pct Infanticidal ¼ 0.4) there is a 40 % chance that
the random number generated will be smaller than the 0.4 specified and thus a 40 %
chance that the new dominant male is infanticidal.
Both of the conditional statements Eqs. (14.2) and (14.3) feed into a biflow connected
to a stock called “Is_the_male_in_the_population_currently_killing_babies?”, which
we used above [Eq. (14.1)] to define the leakage fraction from the stock of infants.
We set the initial condition for this stock to 0. The biflow is called “Change in
Male Status” and has the following value
Change in Male Status ¼ IF Is new male infanticidal? þ Is old male removed? ¼ 2
THEN 6 À Is the male in the population currently killing babies?
ELSE if Is new male infanticidal? À Is old male removed? ¼ À1
THEN À Is the male in the population currently killing babies?
ELSE À 1:
ð14:4Þ
This biflow allows us to make males in the population not perpetual baby killers for
the entire time of their tenure. Instead, after the gestation period of around 6 months
passes, new-borns are likely the male’s offspring, and so this biflow causes the stock to
“count down” until the male gains no benefit from killing babies: If a new male is
successful and is infanticidal, then a six is read in the stock. For each month that the
resident male remains in charge, this value decreases by one until it goes to zero—the
stock is non-negative—and the male is no longer killing babies. If a newly dominant
male is not infanticidal the sum of the two conditional statements is negative.
The stock “Is_the_male_in_the_population_currently_killing_babies?” influences
the infant death rate and the weaning tenure of the females.
124
14 Langur Infanticide and Long-Term Matriline Fitness
varying from just a few days to 74 months. We can assume that each month there is
a 4 % chance of being replaced, so that after the average tenure time passes most
males will have been replaced. (The DT must be set at one for this to work, if DT is
set at 0.5, the 0.96 will have to be replaced by 0.98 so that the same chance is
encountered).
A second unknown is whether the new male (should he win his dominance
challenge) is himself infanticidal. To determine the likelihood that a male commits
infanticide, we specify another random number generator in much the same way,
only this time creating a component called “Pct Infanticidal” in which we can
actually vary the percentage of males in the population who will exhibit this trait. A
converter called “Is_new_male_infanticidal?” uses the random number generator
and the percentage specified to determine the answer to this question. Its value is
Is new male infanticidal ¼ IF Random # Gen 2 <¼ Pct Infanticidal THEN 1
ELSE 0},
ð14:3Þ
such that if 40 % are infanticidal (Pct Infanticidal ¼ 0.4) there is a 40 % chance that
the random number generated will be smaller than the 0.4 specified and thus a 40 %
chance that the new dominant male is infanticidal.
Both of the conditional statements Eqs. (14.2) and (14.3) feed into a biflow connected
to a stock called “Is_the_male_in_the_population_currently_killing_babies?”, which
we used above [Eq. (14.1)] to define the leakage fraction from the stock of infants.
We set the initial condition for this stock to 0. The biflow is called “Change in
Male Status” and has the following value
Change in Male Status ¼ IF Is new male infanticidal? þ Is old male removed? ¼ 2
THEN 6 À Is the male in the population currently killing babies?
ELSE if Is new male infanticidal? À Is old male removed? ¼ À1
THEN À Is the male in the population currently killing babies?
ELSE À 1:
ð14:4Þ
This biflow allows us to make males in the population not perpetual baby killers for
the entire time of their tenure. Instead, after the gestation period of around 6 months
passes, new-borns are likely the male’s offspring, and so this biflow causes the stock to
“count down” until the male gains no benefit from killing babies: If a new male is
successful and is infanticidal, then a six is read in the stock. For each month that the
resident male remains in charge, this value decreases by one until it goes to zero—the
stock is non-negative—and the male is no longer killing babies. If a newly dominant
male is not infanticidal the sum of the two conditional statements is negative.
The stock “Is_the_male_in_the_population_currently_killing_babies?” influences
the infant death rate and the weaning tenure of the females.
124
14 Langur Infanticide and Long-Term Matriline Fitness