Abstract
Worldwide biodiversity faces a variety of anthropogenic threats, including habitat loss and predation by introduced species. Reintroduction has been increasingly successful as a conservation tool to address these threats, but until recently, little attention was paid to securing the genetic health of reintroduced populations. The two major genetic threats to small or bottlenecked populations are inbreeding and loss of allelic diversity. Inbreeding can immediately reduce fitness and increase the risk of extinction, while loss of allelic diversity threatens long-term adaptability. Management for allele retention will also minimise inbreeding and is an effective strategy to maximise genetic viability. In some cases, though, a population may be particularly affected by inbreeding, which then becomes the immediate concern.
Assessing options for genetic management requires accurately predicting inbreeding effects and allele loss under various management scenarios. Such predictions require the use of probability-based individual simulation models, but available models have limitations in being applied to wild, managed populations. Likewise, inbreeding effects are difficult to quantify and include in predictions of viability. The computer tools used to inform genetic management could therefore be greatly improved.
With this thesis, I first describe a new model that I developed to facilitate evaluation of management options for maximising allele retention (Chapter 2). This model is highly flexible and freely available to inform reintroduction planning of a wide variety of taxa. I use the model to explore how demography affects allele retention, finding that while there are broad patterns across taxa, management strategies will need to be tailored to each population of interest (Chapter 3). I also demonstrate application of the model in a context of complex metapopulation management, showing that even small, fragmented populations can be successfully managed for long-term viability (Chapter 4). Appendices A and B exhibit further applications of this model to real-world examples.
I then consider a case in which a great deal of allelic diversity has already been lost and extreme inbreeding has occurred: the black robin. I first demonstrate that further inbreeding produces a mix of positive and negative fitness effects in this species, with important interactions among an individual’s inbreeding coefficient and those of its parents (Chapter 5). Next, I apply these findings in a population viability analysis framework to evaluate the net effect of inbreeding in this species, which is positive and produces a very high probability of persistence if conditions remain stable (Chapter 6). I use this example to demonstrate how other studies could incorporate complex inbreeding effects into population predictions, providing a detailed tutorial in Appendix C. Finally, I assess management options that could be used to improve retention of allelic diversity in the black robin and thus its long-term adaptability to any change (Chapter 7).
Throughout my research, I have collaborated closely with conservation managers to ensure that my analyses are relevant to their work and that my results are available for their use. In Chapter 8, I synthesise the work presented in Chapters 2-7 and explore the general implications of my findings for small or reintroduced populations.