Study: Hobby Hunting Influences the Evolution of Brown Bears

Thirty years of data on Scandinavian brown bears reveal a partly unexpected human influence.

An international team of scientists, with Austrian involvement, tracked the lives of around 900 brown bears in Scandinavia over more than 30 years. An analysis of the data published in the journal «Nature Ecology & Evolution» now shows how profoundly humans influence the lives of these wild animals — and thus their evolution. Hunting in particular has had unexpected effects.

The extensive data once again demonstrate that humans have become the primary driver of evolution, said Andreas Zedrosser, who works at the University College of Southeast Norway in Notodden and at the University of Natural Resources and Life Sciences Vienna. The Carinthian has been involved since the late 1990s in the large-scale «Scandinavian Brown Bear Project», which was launched in 1984. Using radio transmitters, the researchers have since been tracking brown bears, predominantly in Sweden.

Short Lives

Such long-term datasets are rare, and it is often difficult to say much about the lives of large animals with potentially long lifespans — brown bears can, after all, live up to around 30 years. Zedrosser and colleagues therefore aim to scientifically document the lives of the animals from birth to death. In doing so, it became apparent that brown bears rarely reach an advanced age. On average, they live to be only five years old.

In Sweden, around ten percent of the approximately 3,000 brown bears are hunted each year. This quota is relatively high. «The average age at reproduction is around five years. That means many bears never live long enough to produce offspring. That alone shows how significant the impact on the system is,» explained Zedrosser.

The idea that humans have little impact on the lives of these wild animals is therefore mistaken. «We live in the age of the Anthropocene – where humans have simply become the major influencing factor,» said Zedrosser. This had long been underestimated, especially in the case of large animals that live for a long time in relatively natural environments. The extent to which this also applies to the development of the brown bear is now becoming visible even in the far north.

Paradoxical Selection

In addition to unanswered ethical questions, one must also examine how humans are indirectly adapting an animal «precisely to the currently prevailing system.» How this happens is illustrated, for example, by the way young bears are raised: while genetically well-endowed mother bears have offspring roughly every two years, less well-endowed, smaller females typically keep their young with them for an extra year to improve their chances of survival. In Sweden, however, bears traveling in family groups may not be shot. This means that, paradoxically, the survival chances of genetically less well-endowed mothers increase significantly. Zedrosser: «An unconscious selection is taking place in the direction of less reproductive animals.»

In this way, humans trigger genetic changes in the population even when the total number of animals does not change dramatically. This can become a problem if circumstances change, for example due to climate change. Zedrosser: «The ways in which we influence nature often take very different paths than we expect.»