Conclusion
Overall, our study demonstrates how the genetic consequences of linear infrastructure on species is ultimately intrinsically linked to the existing threatening processes and the relative vulnerability of impacted species prior to construction and show how to evaluate the effectiveness of any mitigation measures. Our case study elegantly demonstrates how existing threatening processes (e.g. predation and disease) and the impact of the linear transport infrastructure construction (e.g. translocation and population subdivision) resulted in two subdivided populations with severely reduced census population sizes and decreased effective population size bearing significant genetic costs. However, the intensive koala monitoring and threat management (Beyer et al 2018) along with the reported koala use of culverts post-construction (Dexter et al 2017) and the likely gene flow from adjacent koala populations will go a long way toward continuing to mitigate these potential genetic impacts in the future. Nevertheless, research has shown that genetic erosion, combined with small population size, are significant contributors to population extinction risk (Templeton et al. 2001) and therefore this study has important conservation implications for mitigation on future linear infrastructure development given that mitigations to minimise these costs often fail to adequately address and prevent longer-term genetic impacts.
Acknowledgments. We would like to first acknowledge the First Peoples of Moreton Bay where the fieldwork was undertaken and pay our respect and acknowledge their Elders, past and present. We would like to acknowledge all staff from Endeavour Veterinary Ecology and contractors who worked on the Moreton Bay Rail koala management program. Without their hard work collecting and curating the vast spatial, veterinary, and genetic data set from the Moreton Bay Rail koala management program, this research would not be possible. Moreton Bay Rail koala management program and this research project was funded by the Queensland Government Department of Transport and Main Roads.