Berlin wild boars: The one faithful city borough dwellers, the other from the surrounding area

Berlin’s urban forests harbour isolated wild boar populations, whereas urban wild boars from built-up areas originate from neighbouring rural areas. This is the surprising result of a scientific study by the German Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW), the „Landeslabor Berlin Brandenburg“ and the Natural History Museum in Luxemburg which used techniques from molecular genetics to analyse the structure and origins of the wild boar populations. The study was part of a doctoral dissertation funded by the IZW and financially supported by National Geographic and the Foundation for Nature Conservation Berlin (“Stiftung Naturschutz Berlin”). The results are published in the scientific journal “Journal of Applied Ecology”.

With the spread of urban areas worldwide more wildlife species successfully make their home in this new, human-dominated environment. Berlin, the capital of Germany, for example is often also called the capital of wild boars. Twenty percent of the total area of the state of Berlin is covered with extensive forests, arranged in four main forestry areas which seem to create optimal conditions for wildlife. In Berlin, wild boars do not only occur in the urban forests, they are also regularly seen in urban parks or private gardens where they even raise their piglets.

Urban wildlife populations founded by a few individuals might end up as isolated ‘island’ populations as urban structures might prevent the exchange of individuals with rural populations. An alternative idea suggests that urban areas can receive dispersers from rural areas and maintain a common genetic structure by continuing an exchange of individuals between the city and the countryside. Until now, the origin of Berlin’s urban wild boars was unclear. Are they dispersers from neighbouring urban forests or do they originate from rural areas? Are subpopulations truly isolated or is there an ongoing exchange across the state border between Berlin and Brandenburg? To answer these questions the IZW researchers collected 387 tissue samples from wild boars from Berlin and Brandenburg.

“Surprisingly there are three isolated urban forest populations in Berlin, one in the centre of the Grunewald in the southwest, one in the Tegel forest in the northwest, and one in the Koepenick forest in the southeast, whereas wild boars from the fourth urban forestry area in Pankow in the north are part of one large, continuous population with the wild boars from rural Brandenburg which we studied”, said Leibniz-IZW doctoral student Milena Stillfried who conducted the study. Her analyses showed that there were two independent colonisation events at least – one in the Grunewald and one in the Koepenick forest. The third urban forest population evolved from the neighbouring Grunewald population.

“A surprising fact is that wild boars of built-up urban areas did not – as expected – originate from neighbouring urban forests but came directly from the rural population of Brandenburg”, explains Stillfried. In summary, there are two types of urbanisation processes in Berlin. Firstly, there are isolated urban populations in the urban forests; secondly, urban built-up areas are used as attractive ‘sink’ areas by the rural population in Brandenburg. “We would have never expected that urban structures are mirrored in the genetic structures of the wild boar populations”, said Stephanie Kramer-Schadt and Sylvia Ortmann, who initiated the new research focus “Urban Wildlife Ecology” at the Leibniz-IZW in 2012.

Clearly, these flexible and highly adaptable animals have a knack for colonising novel habitats such as urban environments. Whereas wild boars in rural areas are usually very shy and avoid contact with humans, urban wild boars learn that human proximity per se is not a risk for them and find suitable habitats even in highly built-up areas.  

Genetic structures are often formed or influenced by landscape variables. Might it therefore be possible that the Berlin wall which separated West Berlin from the remaining part of the city and from Brandenburg was also a hurdle for wildlife and therefore played a role during the establishment of the urban Grunewald and Tegel populations in West Berlin? Well, urbanisation of wild boars also occurred in the Koepenick forest in the southeast which did not have the Berlin Wall as a barrier, so it is unlikely that the Berlin Wall is the only explanation for the development of the population structure of wild boars in the Berlin area. A different explanation seems more plausible: The core area of the isolated urban populations are to a large extent surrounded by barriers such as roads or water bodies, which could restrict the mobility of wild boars in all directions – even though  they are able to cross roads in principle and are known to be good swimmers. 

Wild boars in urban areas are well known for the damage they can cause while foraging in private and public gardens. Many people are also scared of the usually peaceful wild boars. These latest scientific findings about the population structure of wild boars in Berlin and Brandenburg will contribute to an understanding of the urbanisation of wildlife and support the authorities in their efforts to minimise conflicts.

Publication:  

Stillfried M, Fickel J, Börner K, Wittstadt U, Heddergott M, Ortmann S, Kramer-Schadt S, Frantz A (2016): Do cities represent sources, sinks or isolated islands for urban wild boar population structure? Journal of Applied Ecology. DOI: 10.1111/1365-2664.12756.

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The Leibniz Institute for Zoo & Wildlife Research (IZW) is an internationally renowned research institute of the Leibniz Association. With the mission of "understanding and improving adaptability" it examines evolutionary adaptations of wildlife and its resilience to global change, and develops new concepts and measures for conservation. To achieve this, the IZW uses its broad interdisciplinary expertise in evolutionary ecology and genetics, wildlife diseases, reproductive biology and management in a close dialogue with stakeholders and the public. The IZW belongs to the Forschungsverbund Berlin e.V.