Extinction vortex

One of the problems of a species becoming rare is that it has to contend with all sorts of additional problems that it didn't have to when it was common.

'Artificial insemination has been considered since the 1990s as a way of reducing inbreeding, but has been hindered by the difficulty of collecting sperm. Early attempts used a fake female kakapo mounted on a radio-controlled toy car, which would approach a male in the midst of his lek display.'

Such is the lot of the unfortunate Kakapo - a species of nocturnal, flightless parrot found only on new Zealand. You know you are in trouble as a species when you all have individual names (unless your species happens to be Homo sapiens). The poor Kakapo, with only 86 individuals alive, all of whom are named, suffers from the effects of genetic drift, inbreeding and demographic stochasticity. We discussed the first two of these on Thursday - genetic drift is a problem because it is likely to lead to the fixation of alleles and the reduction of genetic diversity and inbreeding is a problem because it may lead to an increase in recessive genetic disorders. Demographic stochasticity refers to the random fluctuations in population size and structure that will occur as the population gets smaller (in some ways analagous to genetic drift). For example in 1977, the last 18 Kakapo on an island population in New Zealand were all male.

This increase in problems for a species as it gets rare has been termed an 'extinction vortex' - although how general this is is something of a hot issue.

Hot off the press. Check this out in the library: Quantifying the extinction vortex, Fagan WF, Holmes EE, Ecology Letters 2006, 9:51-60