Multiple life-stage inbreeding depression impacts demography and extinction risk in an extinct-in-the-wild species

Abstract

Inbreeding can depress individuals' fitness traits and reduce population viability. However, studies that directly translate inbreeding depression on fitness traits into consequences for population viability, and further, into consequences for management choices, are lacking. Here, we estimated impacts of inbreeding depression (B, lethal equivalents) across life-history stages for an extinct-in-the-wild species, the sihek (Guam kingfisher, Todiramphus cinnamominus). We then projected population growth under different management alternatives with our B estimates incorporated, as well as without inbreeding depression (B = 0) or with a conventional default B. We found that inbreeding depression severely impacted multiple life-history stages, and directly translated into an effect on population viability under management alternatives. Simulations including our B estimates indicated rapid population decline, whereas projections without inbreeding depression or with default B suggested very gradual population decline. Further, our results demonstrate that incorporation of B across life-history stages can influence management decisions, as projections with our B estimates suggested a need to switch to increased breeding management to avoid species extinction and support wild releases. Our results demonstrate that magnitude of B across life-history stages can translate into demographic consequences, such that incorporation of multiple life-stage B into population models can be important for informed conservation management decision-making.

Figure 1

Census size and inbreeding level through time of the sihek ex-situ population. (a) Number of ex-situ hatched individuals in the population and (b) mean population inbreeding level (f), with standard error bars.

Figure 2

Demographic rates from the sihek ex-situ population used in population models of management scenarios. (a) Number of broods produced and (b) brood size given breeding, (c) proportion of adult females breeding per year (i.e. producing ≥ 1 hatchling) with associated standard deviations, and (d) sex-age class survival probabilities with associated standard deviations. In (d), females and males were pooled for estimation of first-year survival probability. Female fourth-year survival probability represents survival probability of females aged 3 +, male fifth year survival probability represents survival probability of males aged 4 +. For (c) and (d) associated sample sizes are shown above each error bar.

Figure 3

Simulated size of the sihek ex-situ population under alternative management scenarios. Solid lines indicate mean population size across model iterations, with standard deviation (shaded areas). Colours indicate model scenarios including our sihek B estimates (red), no inbreeding depression (blue), or default B (black).