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Integrated population modelling reveals a perceived source to be a cryptic sink
Author(s) -
Weegman Mitch D.,
Bearhop Stuart,
Fox Anthony D.,
Hilton Geoff M.,
Walsh Alyn J.,
McDonald Jennifer L.,
Hodgson David J.
Publication year - 2016
Publication title -
journal of animal ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.134
H-Index - 157
eISSN - 1365-2656
pISSN - 0021-8790
DOI - 10.1111/1365-2656.12481
Subject(s) - emigration , geography , net migration rate , population , immigration , population projection , population growth , ecology , biology , demography , archaeology , sociology
Summary Demographic links among fragmented populations are commonly studied as source‐sink dynamics, whereby source populations exhibit net recruitment and net emigration, while sinks suffer net mortality but enjoy net immigration. It is commonly assumed that large, persistent aggregations of individuals must be sources, but this ignores the possibility that they are sinks instead, buoyed demographically by immigration. We tested this assumption using Bayesian integrated population modelling of G reenland white‐fronted geese ( A nser albifrons flavirostris ) at their largest wintering site ( W exford, I reland), combining capture–mark–recapture, census and recruitment data collected from 1982 to 2010. Management for this subspecies occurs largely on wintering areas; thus, study of source‐sink dynamics of discrete regular wintering units provides unprecedented insights into population regulation and enables identification of likely processes influencing population dynamics at W exford and among 70 other G reenland white‐fronted goose wintering subpopulations. Using results from integrated population modelling, we parameterized an age‐structured population projection matrix to determine the contribution of movement rates (emigration and immigration), recruitment and mortality to the dynamics of the Wexford subpopulation. Survival estimates for juvenile and adult birds at Wexford and adult birds elsewhere fluctuated over the 29‐year study period, but were not identifiably different. However, per capita recruitment rates at Wexford in later years (post‐1995) were identifiably lower than in earlier years (pre‐1995). The observed persistence of the W exford subpopulation was only possible with high rates of immigration, which exceeded emigration in each year. Thus, despite its apparent stability, W exford has functioned as a sink over the entire study period. These results demonstrate that even large subpopulations can potentially be sinks, and that movement dynamics (e.g. immigration) among winters can dramatically obscure key processes driving subpopulation size. Further, novel population models which integrate capture–mark–recapture, census and recruitment data are essential to correctly ascribing source‐sink status and accurately informing development of site‐safeguard networks.