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.