14. Role of Genetics in Conservation Biology
241
pathogens and parasites and hybridization (Woodford and Rossiter 1994; Cunningham 1996; Stockwell et al. 1996). Green and Rothstein (1998), for example,
reported that translocations of the endangered Black-faced Impalas to private
farms have increased the threat of hybridization with resident Common Impalas in
Namibia. They agreed with Robinson and associates (1991) that population manipulations (translocations, introductions) should only be carried out after careful
genetic, taxonomic, and ecological considerations.
Artificial insemination and embryo transfer are alternative methods of introducing genes into a population. Inseminating females or implanting them with
embryos circumvents the problem of mate choice and does not depend on the
establishment and mating success of immigrant males. These methods are, however, highly intrusive, cumbersome, and expensive and hence are only practical
for captive populations and only recommended in cases in which species survival
depends on imminent increase in genetic diversity. Furthermore, reproductive
technology of endangered species is a relatively new and still experimental field.
Although the techniques have proved useful in livestock management, much more
basic research on the reproductive biology of rare species is needed to guarantee
safe application in genetic management efforts (see Ballou and Cooper [1992] and
Moore et al. [1992] for discussion of reproductive technology and conservation
genetics).
In general, increased habitat fragmentation has subdivided many populations to
the point at which individual subpopulations would become extinct unless they
are managed as part of the larger highly structured population. The extreme
complexity of modeling stochastic and deterministic events in such structured
populations has hampered efforts to assess genetic and demographic effects simultaneously (Burgman et al. 1993; Ballou et al. 1995; Ratner et al. 1997).
However, population viability models are becoming increasingly more sophisticated and valuable in risk assessment of endangered populations (Boyce 1992;
Lacy 1993; Kenny et al. 1995; Mills et al. 1996).
Losing Diversity
Inbreeding can be due either to the mating of related individuals (as in selfing or
assortative mating) or it may be because, in finite populations, there is a chance
for two identical genes to be sampled together. This chance increases when the
size of the population decreases. Consequently, levels of homozygosity in inbreeding populations are higher than predicted under random mating (Falconer
and Mackay 1996). (Templeton and Read [1994] discuss different measures of
inbreeding and their relationship with genetic diversity.)
Natural selection is a significant evolutionary force that can maintain or erode
genetic diversity, depending on the relationship between genotypes and fitness.
Directional selection, for example, favors extreme phenotypes and their underlying genotypes, and the entire array of intermediate phenotypes are selected against
241
pathogens and parasites and hybridization (Woodford and Rossiter 1994; Cunningham 1996; Stockwell et al. 1996). Green and Rothstein (1998), for example,
reported that translocations of the endangered Black-faced Impalas to private
farms have increased the threat of hybridization with resident Common Impalas in
Namibia. They agreed with Robinson and associates (1991) that population manipulations (translocations, introductions) should only be carried out after careful
genetic, taxonomic, and ecological considerations.
Artificial insemination and embryo transfer are alternative methods of introducing genes into a population. Inseminating females or implanting them with
embryos circumvents the problem of mate choice and does not depend on the
establishment and mating success of immigrant males. These methods are, however, highly intrusive, cumbersome, and expensive and hence are only practical
for captive populations and only recommended in cases in which species survival
depends on imminent increase in genetic diversity. Furthermore, reproductive
technology of endangered species is a relatively new and still experimental field.
Although the techniques have proved useful in livestock management, much more
basic research on the reproductive biology of rare species is needed to guarantee
safe application in genetic management efforts (see Ballou and Cooper [1992] and
Moore et al. [1992] for discussion of reproductive technology and conservation
genetics).
In general, increased habitat fragmentation has subdivided many populations to
the point at which individual subpopulations would become extinct unless they
are managed as part of the larger highly structured population. The extreme
complexity of modeling stochastic and deterministic events in such structured
populations has hampered efforts to assess genetic and demographic effects simultaneously (Burgman et al. 1993; Ballou et al. 1995; Ratner et al. 1997).
However, population viability models are becoming increasingly more sophisticated and valuable in risk assessment of endangered populations (Boyce 1992;
Lacy 1993; Kenny et al. 1995; Mills et al. 1996).
Losing Diversity
Inbreeding can be due either to the mating of related individuals (as in selfing or
assortative mating) or it may be because, in finite populations, there is a chance
for two identical genes to be sampled together. This chance increases when the
size of the population decreases. Consequently, levels of homozygosity in inbreeding populations are higher than predicted under random mating (Falconer
and Mackay 1996). (Templeton and Read [1994] discuss different measures of
inbreeding and their relationship with genetic diversity.)
Natural selection is a significant evolutionary force that can maintain or erode
genetic diversity, depending on the relationship between genotypes and fitness.
Directional selection, for example, favors extreme phenotypes and their underlying genotypes, and the entire array of intermediate phenotypes are selected against