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Brown bears in Scandinavia

When the project started its genetics studies, it opened a door to new perspectives in the research.  

Four genetic questions were posed:
1. How had bears colonised Scandinavia?
2. How much genetic variation is there?
3. What are the family relationships among bears?
4. How many bears do we have in Sweden?
 

On the basis of these questions, tissue samples of both marked bears and hunter-killed-bears, as well as scat samples were sent to the French genetic researchers Pierre Taberlet and Eva Bellemain and her colleagues. They analysed the DNA, which is unique to each individual.

This is how hereditary factors are transmitted


1. How had the bears colonialise Scandinavia?

Based on mitochondrial DNA (mtDNA), which is matemally transferred, we can maternaly draw conclusions about immigration history. The map shows approximately the areas where 90% of all females occur based on hunter-killed bears.

The result indicates that brown bears colonialised Scandinavia after the last Ice Age about 10-14000 years ago from two directions: from the east and from the south

Almost all females live concentrated in in three areas that we call core areas for reproduction. 
The MtDNA of the brown bears in the southern core area is similar to that of the bears in the Pyrenees and the Cantabrian mountains in France and Spain. These brown bears presumably colonialised Southern Scandinavia after the last Ice Age. 
MtDNA from the bears in the two northern areas is similar to that of Finnish and Russian brown bears. Their forerunners presumably survived the Ice Age in the ice free area west from the Ural Mountains and colonialised Sweden from the east. 
The frontier between the two populations is approximately in the area of Storsjön/Sweden.

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2. How much genetic variation is there?

The two populations do not differ concerning morphology, behaviour and ecology. Analysis of nuclear DNA revealed relatively high genetic variation in the Scandinavian brown bear, even though the poulation has passed through a bottleneck, which usually reduces the genetic variation. (In 1930 the bear was almost exterminated, and there were an estimated 130 individuals in several small isolated areas.) 
The high genetic diversity we found was surprising and may be due to the short bottleneck period (in bear generations) and that the survival of some small isolated populations which later come into contact with each other  may have been positive, as different alleles may have been retained in different populations. 
We have found males in in the North and the South with southern or northern mtDNA, respectively indicating that interchange occurs between the southern and northern brown bears.  The genetic exchange between the different populations is due to the long dispersal of the male bears in their search for females. 

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3. What are the family relationships between bears?

This project concerns genetics at the individual level, f. ex. how bears in a certain area are related to each other. By following marked females for many years we have found out that some females are very successful mothers and some do not succeed at all. It was also observed that some males are together with many more females during mating season than other males. By analysing the nuclear DNA of the cubs from known mothers we can determine paternity of those cubs.
When it is determined which males and females are most successful for reproduction, it is possible to find out how f. ex. the bears' relationships, weight, age and environment can influence individual reproductive success.

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4. How many bears do we have in Sweden?

We have tested, compared and analysed different methods to estimate the population of brown bears. The previous estimation of the bear population size in Sweden is from 1996.  F.ex. We have made a new estimation in Dalarna and Gävleborgs counties in central Sweden in 2001 and 2002 by analysing the DNA from  bear scats collected by moose hunters. Additionally the observations of carnivores by hunters during moose hunting have been registered from 1998, which gives us more knowledge about the population's growth.  The method shows an annual net increase of 4,7% in Sweden generally, with large variation among the counties.

Bear observations by hunters during the first week of moose hunting, corrected for observation time

Results from the genetic analysis of bear scats
In autumn 2001 and 2002 the hunters in Dalarna and Gävleborgs counties collected samples from bear scats they found during the hunting season.  All together there were 1776 samples collected whereof 1327 contained a useable DNA information. With help of these samples it was possible to identify different individuals and their sex.
The coordinates from the scats have been added in the sample report by the hunter. 

 

Here are shown the results from the scat collection in 2001:


The population estimation resulted in a total number of 550 (482-648) bears in Gävleborg and Dalarna. It was not possible to determine which county had the most dense area of bears, because the most dense area is on the county border

The preliminary estimate of number of bears in Sweden is 1635-2840 bears in Sweden in 2004.

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