264
Richard Frankham
Lande and Barrowclough (1987) recommended monitoring of quantitative genetic variation as part of conservation management. However, our results urge
caution in the use of this measure to monitor genetic variation in small populations. Further, simple single-locus models are inadequate to predict the detailed
behavior of quantitative genetic variation in small populations.
Harems
The majority of mammals, plus some birds, reptiles, fish, amphibians, and insects,
have unequal sex ratios of breeding individuals (i.e., polygamy). Harems are the
most extreme form of polygamy. In addition, many species that do not have
harems in nature are maintained in captivity by using harems to avoid aggression
between males. Harems are predicted to reduce N e and so increase the rate of
inbreeding and loss of genetic variation. Briton and associates (1994) confirmed
these predictions. The message is that captive breeders should, as far as possible,
avoid harem breeding structures, especially in those species that do not normally
have them.
Fluctuating Population Sizes
Fluctuating population sizes are common in natural populations of animals. This
is predicted to reduce N e , to increase the rate of inbreeding, and to reduce genetic
diversity. These predictions have been experimentally validated (Woodworth et
al. 1994). Wherever possible, populations should be managed so that there is
minimal variation in population size over generations.
Equalizing Founder Representation
Many captive populations have been founded at the last moment when only a few
individuals of the threatened species remain. These founders often contribute
unequally to future generations, such that the rate of inbreeding and loss of genetic
variation are increased. Consequently, it is recommended that such populations be
managed to equalize founder representation. Experimental evaluation of this recommendation has demonstrated reduced rates of inbreeding and loss of genetic
variation but no benefits in reproductive fitness (Loebel et al. 1992). Surprisingly,
changes in founder representation were almost completed in the first generation.
Computer simulations subsequently showed that this was to be expected when
discrete nonoverlapping generations were used. The mating of individuals connects them, such that the fates of underrepresented and overrepresented founders
can become inextricable bound. Similar effects have been seen in computer simulations comparing the effects of managing small pedigreed populations using
minimum kinship, as compared with maximum avoidance of inbreeding (Ballou
and Lacy 1995). Further theoretical investigations of this issue are warranted.
Richard Frankham
Lande and Barrowclough (1987) recommended monitoring of quantitative genetic variation as part of conservation management. However, our results urge
caution in the use of this measure to monitor genetic variation in small populations. Further, simple single-locus models are inadequate to predict the detailed
behavior of quantitative genetic variation in small populations.
Harems
The majority of mammals, plus some birds, reptiles, fish, amphibians, and insects,
have unequal sex ratios of breeding individuals (i.e., polygamy). Harems are the
most extreme form of polygamy. In addition, many species that do not have
harems in nature are maintained in captivity by using harems to avoid aggression
between males. Harems are predicted to reduce N e and so increase the rate of
inbreeding and loss of genetic variation. Briton and associates (1994) confirmed
these predictions. The message is that captive breeders should, as far as possible,
avoid harem breeding structures, especially in those species that do not normally
have them.
Fluctuating Population Sizes
Fluctuating population sizes are common in natural populations of animals. This
is predicted to reduce N e , to increase the rate of inbreeding, and to reduce genetic
diversity. These predictions have been experimentally validated (Woodworth et
al. 1994). Wherever possible, populations should be managed so that there is
minimal variation in population size over generations.
Equalizing Founder Representation
Many captive populations have been founded at the last moment when only a few
individuals of the threatened species remain. These founders often contribute
unequally to future generations, such that the rate of inbreeding and loss of genetic
variation are increased. Consequently, it is recommended that such populations be
managed to equalize founder representation. Experimental evaluation of this recommendation has demonstrated reduced rates of inbreeding and loss of genetic
variation but no benefits in reproductive fitness (Loebel et al. 1992). Surprisingly,
changes in founder representation were almost completed in the first generation.
Computer simulations subsequently showed that this was to be expected when
discrete nonoverlapping generations were used. The mating of individuals connects them, such that the fates of underrepresented and overrepresented founders
can become inextricable bound. Similar effects have been seen in computer simulations comparing the effects of managing small pedigreed populations using
minimum kinship, as compared with maximum avoidance of inbreeding (Ballou
and Lacy 1995). Further theoretical investigations of this issue are warranted.