Restoration of transborder connectivity for Fennoscandian brown bears (Ursus arctos)

Alexander Kopatz,Oddmund Kleven,Ilpo Kojola,Jouni Aspi,Anita J Norman,Göran Spong,Niclas Gyllenstrand,Love Dalén,Ida Fløystad,Snorre B Hagen,Jonas Kindberg,Øystein Flagstad

doi:10.1016/j.biocon.2020.108936

Abstract

Knowledge about the connectivity among natural populations is essential to identify management units for effective conservation actions. Conservation-minded management has led to the recovery of large carnivore populations in northern Europe, possibly restoring connectivity between the two separated, but expanding brown bear (Ursus arctos) populations on the Scandinavian peninsula to the west and Karelia, a part of the large Eurasian population, to the east. The degree of connectivity between these populations has been poorly understood, therefore we investigated the extent of connectivity between the two populations using autosomal microsatellites and Y chromosome haplotypes in 924 male bears (the dispersing sex), sampled during a period of 12 years (2005–2017) across the transborder area where these two populations meet. Our results showed that the two populations are not genetically isolated as reported in earlier studies. We detected recent asymmetrical gene flow at a rate (individuals per generation) of 4.6–5.5 (1%) from Karelia into Scandinavia, whereas the rate was approximately 27.1–34.5 (8%) in the opposite direction. We estimated historical gene flow of effective number of migrants to be between 1.7 and 2.5 between the populations. Analyses of Y chromosome markers supported these results. Successful recovery and expansion of both populations led to the restoration of connectivity, however, it is asymmetric, possibly due to different recovery histories and population densities. By aligning monitoring between neighboring countries, we were able to better understand the biological processes across the relevant spatial scale.

Highlights

Since isolation can be detrimental to populations and may threaten species survival (Frankham, 2005), wildlife conservation ef forts often seek to establish and maintain inter-population connectivity
K = 2 clusters highlights the east-west division, Scandinavia vs. Karelia, while the substructure with K = 4 clusters is representative of further genetic differentiation within the main clus ters, namely Vasterbotten, Norrbotten/Troms in Scandinavia versus northern Finland/Finnmark and southern Finland in Karelia
Genotypes sampled in Vasterbotten, Troms, Finnmark and southern Finland were mainly assigned to one genetic cluster

Summary

Introduction

Since isolation can be detrimental to populations and may threaten species survival (Frankham, 2005), wildlife conservation ef forts often seek to establish and maintain inter-population connectivity. Assessing connectivity can be challenging, especially on broader, transnational scales, when distances among populations are large and span beyond the average individual dispersal distance of the target species (Flagstad et al, 2003; Vila et al, 2003; Fischer et al, 2017). Because of this and because connectivity is often not balanced or sym metric, transborder assessment of populations across the entirety of their distribution range is preferable (Beger et al, 2010; Sundqvist et al, 2016; Thornton et al, 2018). Genetic data is important as demographic connectivity alone is not a feasible indicator for successful reproduction and genetic connectivity (Allendorf et al, 2010; McMahon et al, 2014; Shafer et al, 2015)

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Discussion

Conclusion