Conservation genetics – molecular detectives at work
Box 2 | The problem of small populations
Most of our threatened species exist only in small populations. For example, one of Australia’s most endangered animals, the northern hairy-nosed wombat, has only about 70 individuals, while the bridled nailtailed wallaby consists of only a few hundred individuals in a single population.
In the 1980s, conservation biologists became concerned about genetic problems that might arise within such small populations. One reason was that since small populations generally have low genetic variability, their capacity to adapt to environmental change – to evolve – is also low. Therefore, their ability to survive in the long term becomes doubtful.
Another reason was the problem of inbreeding depression – the tendency of closely related organisms to produce offspring with deformities that limit their chances of survival. This is probably the reason behind the taboo in most human societies against marriage between close relatives.
There are many other reasons to fear for a species when its numbers are low. In recent years, ecologists have argued that environmental pressures posed by feral animals, land clearing, fire and other threats will wipe out many species long before they succumb to problems arising from their low genetic variation.
With this in mind, ecologists and conservation geneticists have attempted to combine all possible threats in the concept of ‘minimum viable population’ (MVP). This is the smallest possible population that has a good chance of surviving in the face of genetic, environmental and other pressures. Population viability analysis works out the MVP for different threatened species, which conservation managers then use in their efforts to conserve the species.
Boxes
Box 1. What is genetics?
Box 3. Molecular detectives at work
Related site
Blood in the water (The Why Files, USA)
Posted August 1999.