Role of Genetics in Conservation Biology

Conclusions

Which species are most at risk of extinction may depend on many interactive aspects of their biology, such as their ecology (e.g., specialists), mating or migratory behavior (e.g., threatened breeding or wintering grounds), demography (e.g., low birth rate), and population genetics (e.g., small effective population size). Populations that are dwindling in size are generally marked by high mortality or low birth rates and eventually may show changes in gene frequencies due to increased population subdivisions and reduced gene flow. Hence, ecologists make use of alarming demographic trends such as low growth rates and conservation geneticists focus on changes in genetic variation (e.g., loss of heterozygosity) to screen for possible threatened populations. Population viability analyses that estimate extinction risks of populations due to both demographic and genetic stochasticity provide powerful monitoring tools that will help to guide the allocation of scarce resources to taxa most likely in need of management (Burgman et al. 1988; Lacy 1993; Nunney and Campbell 1993; Ballou et al. 1995).

Failure to detect signs of increased extinction risk based on the demographic and genetic records of populations should not be interpreted as a guarantee of survival of a taxon, especially not for healthy populations with a limited range or species of a specialized ecological niche that might become endangered by a single catastrophic event. Hence listing taxa as endangered should be based on demographic and genetic indicators of decline, while taking into consideration vulnerabilities of the species due to its specific biology, as well as abiotic factors such as the local political situation (Avise 1994; Ballou et al. 1995; Avise and Hamrick 1996). In their reevaluation of the IUCN threatened species categories, Mace and Lande (1991) applied a similar logic in their development of quantitative criteria to determine endangerment.