Metapopulation effective size and conservation genetic goals for the Fennoscandian wolf (Canis lupus) population

Abstract

The Scandinavian wolf population descends from only five individuals, is isolated, highly inbred and exhibits inbreeding depression. To meet international conservation goals, suggestions include managing subdivided wolf populations over Fennoscandia as a metapopulation; a genetically effective population size of Ne⩾500, in line with the widely accepted long-term genetic viability target, might be attainable with gene flow among subpopulations of Scandinavia, Finland and Russian parts of Fennoscandia. Analytical means for modeling Ne of subdivided populations under such non-idealized situations have been missing, but we recently developed new mathematical methods for exploring inbreeding dynamics and effective population size of complex metapopulations. We apply this theory to the Fennoscandian wolves using empirical estimates of demographic parameters. We suggest that the long-term conservation genetic target for metapopulations should imply that inbreeding rates in the total system and in the separate subpopulations should not exceed Δf=0.001. This implies a meta-Ne of NeMeta⩾500 and a realized effective size of each subpopulation of NeRx⩾500. With current local effective population sizes and one migrant per generation, as recommended by management guidelines, the meta-Ne that can be reached is ~250. Unidirectional gene flow from Finland to Scandinavia reduces meta-Ne to ~130. Our results indicate that both local subpopulation effective sizes and migration among subpopulations must increase substantially from current levels to meet the conservation target. Alternatively, immigration from a large (Ne⩾500) population in northwestern Russia could support the Fennoscandian metapopulation, but immigration must be substantial (5–10 effective immigrants per generation) and migration among Fennoscandian subpopulations must nevertheless increase.

Do estimates of contemporary effective population size tell us what we want to know?

“…Applying the above line of reasoning from Laikre et al () all metapopulations and their subpopulations discussed in this paper would be considered genetically “safe”, meeting the long‐term goal of N e > 500, before migration‐drift equilibrium has been attained. This happens when the N eIRx of the smallest subpopulation exceeds 500, which occurs in generation t = 78, t = 13, and t = 577 for Figures , and , respectively.…”

“…In the present example with m' = 0.002, for instance, the N eIRx = 500 criterion will be met in generation t ≈ 275. At this time, however, local inbreeding has increased to f > 0.75, a value that would most likely be considered unacceptably high in the context of genetic conservation (see Laikre et al, and below).…”

“…In this paper we use the wider approach and consider the joint effects of drift and migration when defining effective size of a local population in a metapopulation. We follow the nomenclature of Laikre et al () and Olsson, Laikre, Hössjer, and Ryman () and make a distinction between N e of a local population “ x ” under isolation ( N ex , which is the same for all types of genetic drift) and the realized effective size of subpopulation x when the joint effects of drift and migration are taken into account (e.g., N eIRx or N eVRx ; Table ). We note here that realized effective size is the quantity being estimated when sampling from a local population under migration and applying an unbiased estimator.…”

“…In this paper we use the wider approach and consider the joint effects of drift and migration when defining effective size of a local population in a metapopulation. We follow the nomenclature of Laikre et al (2016) and Olsson, Laikre, Hössjer, and Ryman (2017) and make a distinction between N e of a local population "x" under isolation (N ex , which is the same for all types of genetic drift) and…”

“…As an example, we applied this analytical tool to model the case of the wolf metapopulation on the Fennoscandian peninsula and showed that the observed unidirectional gene flow from Finland to Sweden greatly reduces the overall metapopulation inbreeding effective size. Further, gene flow from a large Russian wolf population into the Fennoscandian metapopulation has limited effect on inbreeding rates unless gene flow within Fennoscandia increases substantially (Laikre, Olsson, Jansson, Hössjer, & Ryman, ). These observations were previously unknown phenomena of direct relevance to management.…”