Threatened NZ Birds
Informing genetic management of small populations
From 2011 to 2014, I worked toward my PhD at the University of Otago in Dunedin, New Zealand, supervised by Prof Ian Jamieson and Dr Catherine Grueber. Our research group was affiliated with the Allan Wilson Centre for Molecular Ecology and Evolution, and we worked closely with New Zealand's Department of Conservation. My PhD thesis (equivalent to a dissertation in North American terms) was awarded a place on the list of Exceptional PhD Theses in the Division of Sciences at the University of Otago.
My research examined options for managing genetic diversity and inbreeding, with the aim of improving population viability. I developed quantitative tools toward this purpose, and used several New Zealand forest birds (especially kiwi, kokako, and black robin) as model species to address these issues.
Most of New Zealand's native land birds are threatened or declining due to introduced mammalian predators (e.g. stoats, rats, and cats). Populations of several native species have been established on offshore islands or fenced mainland sanctuaries from which all introduced mammals have been removed. These protected populations are a great insurance policy for the threatened species.
However, many of these reserves are quite small, so the protected populations are necessarily small as well. Also, relatively few individuals (< 50, < 20, or even just 2 in the case of the black robin!) are usually used to start the populations. In some cases, the entire species has been through a moderate to severe genetic bottleneck. These factors mean the populations are vulnerable to genetic problems and may not be able to persist long-term.
My PhD work focused on assessing options for establishing and maintaining genetically viable populations, using real populations of threatened NZ birds as case studies. For example, I developed a model to predict allele loss and accumulation of inbreeding in small populations. This model can be applied to any animal, and is freely available as an R package called AlleleRetain, which was also the basis of two published papers
I used AlleleRetain to advise translocations of kiwi (two species in several reserves), metapopulation management of kokako (>20 populations), and genetic viability of Laysan ducks in Hawaii.
Another large part of my PhD involved assessing the effect of inbreeding depression on the viability of black robins. In 1980, there were only 5 black robins left - including just one viable breeding pair. The species has rebounded with the help of predator control and habitat restoration; but all 280 black robins alive today are descended from that one breeding pair, and are more closely related to each other than siblings in a normal population! We found a very interesting mix of negative and - surprisingly - positive effects of inbreeding on fitness (especially chick and juvenile survival) for black robins. A population viability analysis revealed that inbreeding per se will not threaten the persistence of this species, but that further loss of genetic diversity will be problematic if there are any changes in environmental conditions.
