Comparison of three techniques for genetic estimation of effective population size in a critically endangered parrot

Abstract

Understanding the current population size of small, spatially aggregating populations of species is essential for their conservation. Reliable estimates of the effective population size (Ne) can be used to provide an early warning for conservation managers of the risks to genetic viability of small populations. Critically endangered, migratory swift parrots Lathamus discolor exist in a single panmictic population in Australia. In their Tasmanian breeding range, they are at severe risk of predation by introduced sugar gliders, exacerbated by deforestation. We used three genetic approaches to estimate Ne using DNA samples genotyped by microsatellite markers and existing life‐history data of swift parrots. Based on all samples, we revealed small contemporary Ne estimates across methods (range: 44–140), supporting the need to urgently address threatening processes. Using the 0.5 Ne/N ratio calculated from demographic data suggests that the minimum potential contemporary population size is below 300 individual swift parrots. This is considerably lower than the published estimates derived from expert elicitation, and accords with modeled estimates of extinction risk in this species. Our study has important implications for other threatened species with unknown population sizes and demonstrates that by utilizing available genetic data, reasonable estimates of Ne can be derived.

Long‐term ecological data confirm and refine conservation assessment of critically endangered swift parrots

“…Allee effects likely exist in swift parrots and these are ignored in our models but are likely to exert a negative effect on population growth (Crates et al ., 2017). Further, we applied the most recent published population estimate in our contemporary model (Webb et al ., 2021), although ongoing genetic research suggests this value may be lower (Olah et al ., 2021). Finally, we ignore the effect of introduced nest competitors, such as starlings Sturnus vulgaris , which may reduce the carrying capacity of existing nesting areas (Stojanovic et al ., 2020 a ).…”

Population genomic monitoring provides insight into conservation status but no correlation with demographic estimates of extinction risk in a threatened trout

“…After removing hybrid individuals, our results suggest LCT populations have concerningly low levels of genetic variation overall. Evaluation of the quantitative values of genomic metrics themselves, for comparison to other studies for example, is difficult given different filtering and analytical methods (De la Cruz & Raska, 2014; Diaz‐Arce & Rodriguez‐Ezpeleta, 2019), but effective population size is a transferable metric of genetic status (Antao et al, 2010; Carroll et al, 2018; Leroy et al, 2018) that can provide an early warning about genetic risks (Hohenlohe et al, 2021; Olah et al, 2021) and with guidance on minimum sizes necessary for ensuring persistence and evolutionary capacity (Frankham et al, 2014; Franklin, 1980; Traill et al, 2010). However, because it can be difficult to measure accurately with whole population sampling such as ours (Serbezov et al, 2012; Waples et al, 2014), recent studies have demonstrated the benefit of the cohort‐based metric effective number of breeders ( N b ) as potentially useful for gaging abundance (Ferchaud et al, 2016; Luikart et al, 2020).…”

Advancing Genetic Methods in the Study of Parrot Biology and Conservation

“…On the island of Tasmania and its own offshore islands, a study of the migratory Swift Parrot Lathamus discolor could not detect genetic differentiation among breeding populations in consecutive years and across multiple islands [133]. Genetic estimations were used to calculate the effective population size of their single, panmictic population, and after combining it with demographic data, the study calculated a potential contemporary population size as low as 300 individuals [134].…”