Brown bears are sweet-tooth gardeners

The brown bear is colloquially known as “the repentant carnivore” because of its vegetarian diet. Now a new study shows that this plant-based diet is beneficial not only for bears but also for the plants eaten because they disperse their seeds, and that this is a global phenomenon. Worldwide, brown bears consume large amounts of fleshy fruits and from more than a hundred plant species. The seeds of these fruits are later defecated undamaged in new places and may germinate most of the times, the study finds. 

Brown bears like sugar-rich foods such as flehsy fruits. This is common knowledge for anyone who watched Yogi the bear and Boo Boo. However, we still do not know much about how good is for a fruit to be eaten by a bear. An international research team from Poland, Germany, and Spain compiled information about the importance of fruits in the diet of this species from 96 different populations of Europe, Asia and North America. They found that brown bears eat more than a hundred different species of fruits and that they represent a quarter of brown bears’ diet worldwide. 

As eating large amounts of fruits of many different species is not enough to prove that bears are good “gardeners”, the researchers also performed a germination experiment to check if the seeds of the fruits eaten by bears can germinate. The scientists collected fruits from 11 species that are commonly eaten by bears in central Europe, they fed captive bears with these fruits, collected the scats, extracted the seeds and sowed them. They discovered that seeds recovered from bear scats germinate better than seeds embedded within fruit’s pulp. “We already knew that brown bears like fruits but now we demonstrate that it is also beneficial for fruited-plant species. In fact, for a seed it is much better to be eaten by bears than to remain in the plant”, says Alberto García-Rodríguez, leading author of the study. Nuria Selva, supervisor of the study, highlights: “Brown bears seem to swallow the fruits without chewing them a lot. This explains why we found a large proportion of undamaged seeds in the bear scats”. 

Selva also refers to another interesting behavior that makes brown bears efficient “gardeners”: “Brown bears often defecate close to their beds, which they prepare every day by digging the vegetation so they feel more comfortable when laying on the ground. This digging behavior may also facilitate the germination of the seeds. We are currently investigating this”. 

The study highlights the importance of large animals, also called megafauna, in dispersing seeds in northern latitudes. “During the last centuries, humans have extirpated most of the large frugivores from many areas. Some species, such as elephants and rhinos, still remain in the tropics, and have a key role in the dispersal of seeds and the survival of the plants. The absence of other large frugivores in non-tropical regions implies that, in these areas, bears are the only animals able to move seeds over long distances from the places where they feed”. “These long-distance movements are essential for plants because they guarantee the exchange of genetic information among plant populations and facilitate the colonization of new areas” García-Rodríguez concludes.   

This study, just published in Scientific Reports, was led by researchers from the Institute of Nature Conservation (Polish Academy of Sciences) in collaboration with the Senckenberg Biodiversity and Research Centre and the University of Marburg in Germany, the Institute of Natural Products and Agrobiology of the Spanish Research Council in Spain and the Workshop for All Beings Association in Poland. The research took part within the framework of the BearConnect project, an international project taking the brown bear as a model to analyse the connectivity and sustainability of European protected areas.

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Hembra de oso pardo y su cachorro en un prado de arándanos (Vaccinium myrtillus, Ericaceae) en las montañas Tatra, Polonia