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Research article - Peer-reviewed, 2021

Using long‐term data for a reintroduced population to empirically estimate future consequences of inbreeding

Armstrong, Doug P.; Parlato, Elizabeth H.; Egli, Barbara; Dimond, Wendy J.; Kwikkel, Renske; Berggren, Åsa; McCready, Mhairi ; Parker, Kevin A.; Ewen, John G.


Inbreeding depression is an important long-term threat to reintroduced populations. However, the strength of inbreeding depression is difficult to estimate in wild populations because pedigree data are inevitably incomplete and because good data are needed on survival and reproduction. Predicting future population consequences is especially difficult because this also requires projecting future inbreeding levels and their impacts on long-term population dynamics, which are subject to many uncertainties. We illustrate how such projections can be derived through Bayesian state-space modeling methods based on a 26-year data set for North Island Robins (Petroica longipes) reintroduced to Tiritiri Matangi Island in 1992. We used pedigree data to model increases in the average inbreeding level (F) over time based on kinship of possible breeding pairs and to estimate empirically Ne/N (effective/census population size). We used multiple imputation to model the unknown components of inbreeding coefficients, which allowed us to estimate effects of inbreeding on survival for all 1458 birds in the data set while modeling density dependence and environmental stochasticity. This modeling indicated that inbreeding reduced juvenile survival (1.83 lethal equivalents [SE 0.81]) and may have reduced subsequent adult survival (0.44 lethal equivalents [0.81]) but had no apparent effect on numbers of fledglings produced. Average inbreeding level increased to 0.10 (SE 0.001) as the population grew from 33 (0.3) to 160 (6) individuals over the 25 years, giving a urn:x-wiley:08888892:media:cobi13646:cobi13646-math-0001 ratio of 0.56 (0.01). Based on a model that also incorporated habitat regeneration, the population was projected to reach a maximum of 331–1144 birds (median 726) in 2130, then to begin a slow decline. Without inbreeding, the population would be expected stabilize at 887–1465 birds (median 1131). Such analysis, therefore, makes it possible to empirically derive the information needed for rational decisions about inbreeding management while accounting for multiple sources of uncertainty.


Bayesian hierarchical modeling; inbreeding depression; New Zealand; North Island robin; population modeling; reintroduction; small populations; Toutouwai

Published in

Conservation Biology
2021, volume: 35, number: 3, pages: 859-869

Authors' information

Armstrong, Doug P.
Massey University
Parlato, Elizabeth H.
Massey University
Egli, Barbara
Massey University
Dimond, Wendy J.
Massey University
Kwikkel, Renske
Wageningen University and Research
Swedish University of Agricultural Sciences, Department of Ecology
McCready, Mhairi
Hihi Conservation Charitable Trust
Parker, Kevin A.
Parker Conservation
Ewen, John G.
Zoological Society of London

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