Research implications
Field research to understand current vital rates and dispersal dynamics
is urgently required to quantify the fitness costs of high inbreeding
and low genetic diversity in the King Island scrubtit as these costs can
be high (Harrisson et al. 2019; Kardos et al. 2023). The relative
contribution of genetic effects associated with the taxon’s small and
fragmented population to its decline can then be compared to other known
threats such as predation by feral cats. This information can help
prioritise implementation of recovery actions to address the most
prominent threats facing the taxon. We consider two particular
priorities are to determine: (1) whether contemporary breeding success
and juvenile recruitment in King Island scrubtit are low, and if so
whether this is primarily due to inbreeding depression (e.g. Duntsch et
al. 2023), high predation rates (e.g. Crates et al. 2019) or simply a
severe shortage of breeding resources (i.e. habitat saturation, Komdeur,
1992); and (2) whether any surviving juveniles are able to successfully
disperse between subpopulations. Our data suggest successful juvenile
dispersal is unlikely, in which case juveniles (i) remain in their natal
areas without breeding; (ii) breed with close relatives; or (iii) die
during dispersal. Under such scenarios, translocation of juveniles
between subpopulations could facilitate genetic rescue with minimal risk
to the current effective population (Frankham et al. 2015).
More broadly, our study highlights the potential for avoidable
biodiversity loss to occur when the conservation requirements of less
enigmatic or geographically remote taxa are overlooked (Woinarski et al.
2017). It also highlights the challenges of implementing effective
conservation measures when basic population monitoring data are lacking
(Lindenmayer et al. 2020). The conservation status of the King Island
scrubtit has been known for decades (Garnett et al. 2011), however
targeted research to establish the species’ basic ecological
requirements is ongoing (Webb et al. 2016, Bell et al. 2023). Population
genomics is itself an important tool for implementing evidence-based
conservation, but is most effective at preventing extinctions when
complemented with rigorous, field-based population monitoring data
(Taylor et al. 2017, Duntsch et al. 2023).