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).