Dataset Information

Genetic and demographic recovery of an isolated population of brown bear Ursus arctos L., 1758.

ABSTRACT: The brown bear Ursus arctos L., 1758 population of the Cantabrian Mountains (northwestern Spain) became isolated from other bear populations in Europe about 500 years ago and has declined due to hunting and habitat degradation. At the beginning of the 20th century, the Cantabrian population split into eastern and western subpopulations, and genetic exchange between them ceased. In the early 1990s, total population size was estimated to be < 100 bears. Subsequently, reduction in human-caused mortality has brought about an increase in numbers, mainly in the western subpopulation, likely promoting male-mediated migration and gene flow from the western nucleus to the eastern. To evaluate the possible genetic recovery of the small and genetically depauperate eastern subpopulation, in 2013 and 2014 we genotyped hair and faeces samples (116 from the eastern subpopulation and 36 from the western) for 18 microsatellite markers. Data from the annual count of females with cubs of the year (COY) during the past twenty-six years was used to analyze demographic changes. The number of females with COY fell to a minimum of seven in the western and three in eastern subpopulations in the biennium 1993-1994 and reached a respective maximum of 54 and 10 individuals in 2013-2014. We also observed increased bear dispersal and gene flow, mainly from the western to the eastern subpopulation. Of the 26 unique genotypes detected in the eastern subpopulation, 14 (54%) presented an admixture composition, and seven (27%) were determined to be migrants from the western subpopulation. Hence, the two separated and clearly structured subpopulations identified in the past currently show some degree of genetic admixture. This research shows the partial demographic recovery and a change in genetic composition due to migration process in a population of bears that has been isolated for several centuries.

SUBMITTER: Gonzalez EG

PROVIDER: S-EPMC4860320 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Publications

Genetic and demographic recovery of an isolated population of brown bear Ursus arctos L., 1758.

Gonzalez Elena G EG Blanco Juan C JC Ballesteros Fernando F Alcaraz Lourdes L Palomero Guillermo G Doadrio Ignacio I

PeerJ 20160428

The brown bear Ursus arctos L., 1758 population of the Cantabrian Mountains (northwestern Spain) became isolated from other bear populations in Europe about 500 years ago and has declined due to hunting and habitat degradation. At the beginning of the 20th century, the Cantabrian population split into eastern and western subpopulations, and genetic exchange between them ceased. In the early 1990s, total population size was estimated to be < 100 bears. Subsequently, reduction in human-caused mort ...[more]

PMID: 27168963

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Project description:The degree of gene flow within and among populations, i.e. genetic population connectivity, may closely track demographic population connectivity. Alternatively, the rate of gene flow may change relative to the rate of dispersal. In this study, we explored the relationship between genetic and demographic population connectivity using the Scandinavian brown bear as model species, due to its pronounced male dispersal and female philopatry. Thus, we expected that females would shape genetic structure locally, whereas males would act as genetic mediators among regions. To test this, we used eight validated microsatellite markers on 1531 individuals sampled noninvasively during country-wide genetic population monitoring in Sweden and Norway from 2006 to 2013. First, we determined sex-specific genetic structure and substructure across the study area. Second, we compared genetic differentiation, migration/gene flow patterns, and spatial autocorrelation results between the sexes both within and among genetic clusters and geographic regions. Our results indicated that demographic connectivity was not a reliable indicator of genetic connectivity. Among regions, we found no consistent difference in long-term gene flow and estimated current migration rates between males and females. Within regions/genetic clusters, only females consistently displayed significant positive spatial autocorrelation, indicating male-biased small-scale dispersal. In one cluster, however, males showed a dispersal pattern similar to females. The Scandinavian brown bear population has experienced substantial recovery over the last decades; however, our results did not show any changes in its large-scale population structure compared to previous studies, suggesting that an increase in population size and dispersal of individuals does not necessary lead to increased genetic connectivity. Thus, we conclude that both genetic and demographic connectivity should be estimated, so as not to make false assumptions about the reality of wildlife populations.

Project description:Over the centuries, the geographical distribution of brown bear (Ursus arctos) across the Iberian Peninsula has been decreasing, with the species currently confined to North Iberia. The Cantabrian brown bear population is one of the smallest in Europe and is structured into two subpopulations, positioned along an east-west axis. Given the current critically endangered status of this population, it is essential to have a clear picture of its within-population genetic patterns and processes. We use a set of three molecular markers (mitochondrial DNA, autosomal microsatellites and sex markers) to clarify the genetic origins and assess the migration patterns and gene flow of the Cantabrian brown bear population. Our results reveal the presence of two different mitochondrial (matrilineal) haplotypes in the Cantabrian population, both belonging to European brown bear clade 1a. The two haplotypes are geographically structured between Eastern (haplotype CanE) and Western Cantabrian (haplotype CanW) subpopulations, which is consistent with the genetic structure previously identified using nuclear markers. Additionally, we show that CanE is closer to the historical Pyrenean (Pyr) haplotype than to CanW. Despite strong structuring at the levels of mtDNA and nuclear loci, there is evidence of bidirectional gene flow and admixture among subpopulations. Gene flow is asymmetrical and significantly more intense from the Eastern to the Western Cantabrian subpopulation. In fact, we only detected first generation male migrants from the Eastern to the Western Cantabrian subpopulation. These results suggest more intense migration from the smaller and more vulnerable Eastern Cantabrian subpopulation towards the larger and more stable Western Cantabrian subpopulation. These new insights are relevant for assessments of on-going conservation measures, namely the role of dispersal corridors and enhanced connectivity. We discuss the importance of complementary conservation measures, such as human-wildlife conflict mitigation and habitat improvement, for the conservation of a viable Cantabrian brown bear population.

Project description:Many large carnivore populations are expanding into human-modified landscapes and the subsequent increase in coexistence between humans and large carnivores may intensify various types of conflicts. A proactive management approach is critical to successful mitigation of such conflicts. The Cantabrian Mountains in Northern Spain are home to the last remaining native brown bear (Ursus arctos) population of the Iberian Peninsula, which is also amongst the most severely threatened European populations, with an important core group residing in the province of Asturias. There are indications that this small population is demographically expanding its range. The identification of the potential areas of brown bear range expansion is crucial to facilitate proactive conservation and management strategies towards promoting a further recovery of this small and isolated population. Here, we used a presence-only based maximum entropy (MaxEnt) approach to model habitat suitability and identify the areas in the Asturian portion of the Cantabrian Mountains that are likely to be occupied in the future by this endangered brown bear population following its range expansion. We used different spatial scales to identify brown bear range suitability according to different environmental, topographic, climatic and human impact variables. Our models mainly show that: (1) 4977 km2 are still available as suitable areas for bear range expansion, which represents nearly half of the territory of Asturias; (2) most of the suitable areas in the western part of the province are already occupied (77% of identified areas, 2820 km2), 41.4% of them occurring inside protected areas, which leaves relatively limited good areas for further expansion in this part of the province, although there might be more suitable areas in surrounding provinces; and (3) in the eastern sector of the Asturian Cantabrian Mountains, 62% (2155 km2) of the land was classified as suitable, and this part of the province hosts 44.3% of the total area identified as suitable areas for range expansion. Our results further highlight the importance of increasing: (a) the connectivity between the currently occupied western part of Asturias and the areas of potential range expansion in the eastern parts of the province; and (b) the protection of the eastern sector of the Cantabrian Mountains, where most of the future population expansion may be expected.

Dataset Information

Genetic and demographic recovery of an isolated population of brown bear Ursus arctos L., 1758.

Publications

Genetic and demographic recovery of an isolated population of brown bear Ursus arctos L., 1758.

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