9643

• UCREFRP Catalog Number: 9643
• Author: Seener, J. W.
• Title: Inbreeding Depression and the Survival of Zoo Populations
• USFW Year: n.d.
• USFW - Doc Type: 209-217
• Copyright Material: YES

40

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SENNEA/CHAPTER12
INBREEDING DEPRESSION AND THE SURVIVAL OF ZOO POPULATIONS

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a:
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I-
Z
W
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a:
W
11.

INITIAL
POPULATION
SIZE

CAPTIVE
RELATEDNESS

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a:
::::l
en 50
I-
Z
W
U
a:
W
11.

10

the right) initiated at. the population size given on the abscissa. The
Dlber of generations taken to reach f == 0.60 is given on the ordinate.
r all maintenance population sizes, increasing the initial population
ze from two to four or five greatly lengthens the time for the inbreeding
fficient to increase to 0.60, but increasing the initial population much
above five has little affect on survival.

20
GENERATION

FIGURE 7. The sensitivity of the
model to the relatednes. of
founder animal..

FIGURE 8. The sensitivity of the
model to variation in the number
of founder..

Maintenance Population Size

In contrast, the corresponding Figures 10 and 11 demonstrate that
increases in the maintenance population size result in proportional in-
creases in survival. Figure 10 shows how varying the maintenance popula-
tion size affects the probability of survival to the generation given on the
abscissa. The standard population size used on all other figures was 10. In
Figure 11 each line represents sets of populations started at the given
initial population size (2, 5, 20, 50). Each population was then maintained
at the size given on the abscissa, with the number of generations required
to reach an f of 0.60 given on the ordinate. This shows that effort put into

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ulation size (M). I assume that the population has effective size I when
captured, then increases to size M in one generation and remains at that
population size until reproduction falls below the replacement level. Fig-
ure 8 demonstrates the effect of varying the initial population size around
the ~tandard val~~ ~f four used on all other figures. The probability of
sul'v1v~1 for an lDltlal effective population size of four (the standard
value) IS much closer to the survival rate of an effective size of 10 than to
that o~ ~.eff~tive size of two. This implies a nonlinear relationship be-
tween Imtial size and survival. In Figure 9 this relationship is viewed in
anothe~ way by ~lculating the increase in the inbreeding coefficient per
generation for vanous population management scenarios and then deter-
mining the num.ber of generations required to reach the ~bitrary value of
f == 0.60. Each line represents a fixed maintenance population size (shown

MAINTENANCE
POPULATION
SIZE

50

15

~
Q 0 100
I-CO
<0
ffi II 80
f5 ~ 60
C.!)u
u.. < 40
OW
a: a:
wO
ml-
::E
::::l
Z

50

4 7 10

en
z 100
glB
<0 80 r 50
ffi II
z- 60 35
WJ: r
C.!)u FIGURE 9. The e1fect of
u..< 40
OW 20 Increa.ing the initial population
a: a: 20
wO size on the numbers of generations
ml-
::E it take. to reach f - 0.80. The
::::l 0 5 10 15 20 number at the end of each curve i8
z
INITIAL POPULATION SIZE the maintelUlllCe size.
218

o 20 40
GENERATION

FIGURE 10. The sensitivity of the
nlodel to c:Wl'erent maintenance
sizes.

20 5
2
o 10 20 30 40 50
MAINTENANCE POPULATION SIZE

FIGURE 11. The effect of
maintenance size on the number
of generations it takes to reach f
== 0.60. The number at the origin
of each line is the founder size.

217