Conservation implications
The principal threat to persistence of the King Island scrubtit is
habitat loss and its small population size (Threatened Species Section,
2012). Preservation of remaining habitat and restoration of lost habitat
will therefore be critical if the taxon is to recover in the longer term
(Webb et al. 2016). In the shorter term, our results suggest the Pegarah
Forest, Colliers Swamp and Nook Swamps subpopulations of the King Island
scrubtit should be managed as a single management unit with
translocations between these small, isolated populations used to improve
gene flow that has been lost due to habitat fragmentation and ensure
that the current level of overall genetic diversity is maintained
(Frankham et al 2017). Higher levels of inbreeding, lower estimated
effective population sizes and higher probability of visible defective
traits (i.e. baldness) relative to the Tasmanian scrubtit suggest that
genetic factors may well be exacerbating population decline in King
Island scrubtits. Future genetic management of the population is
therefore warranted. There are currently no demographic data on
dispersal and breeding success rates in King Island scrubtits. However,
if breeding success is low and / or contemporary gene flow between
subpopulations is as infrequent as our results suggest, genetic rescue
through the translocation of scrubtits between King Island
subpopulations could help (Harrisson et al. 2016).
Action paralysis is a conscious management decision when threats are
known, and risks of adverse events may be worth taking if a species or
population is already known to be on a course for imminent extinction
(Webb et al. 2018, Canessa et al. 2020). For many years, the risk of
outbreeding depression has been used as an excuse for inaction (Ralls et
al. 2018), however evidence for outbreeding depression is limited and
predictable (Frankham et al. 2011, Frankham 2015). A very real risk of
any translocation is that introduced individuals may be vectors for the
establishment of novel pathogens in threatened populations (Peters et
al. 2014), however this risk can be mitigated with disease screening.
The current rate of King Island scrubtit population decline, and the
extent to which this decline is exacerbated by genetic effects are
currently unknown. Our results suggest two precautionary approaches to
genetic management of King Island scrubtits are feasible. Assuming that
delaying management will not compromise the chances of future King
Island scrubtit population recovery, the Tasman Peninsula subpopulation
of Tasmanian scrubtits could be used as a trial for genetic rescue,
given the remarkable similarity of this subpopulation’s genetic
parameters to the King Island scrubtit. If conservation actions are
considered urgent, genetic rescue trials could occur in the Pegarah
Forest King Island scrubtit subpopulation, which our data suggest is
most at risk of inbreeding and extinction, with minimal risks of
negative genetic effects spreading to the other two subpopulations via
natural gene flow.