Bears are true omnivores. This flexibility has enabled them to successfully survive in a wide variety of habitats. An international research team led by Senckenberg scientist Dr. Jörg Albrecht has now analyzed ecological and paleoecological data on seven bear species on a large scale for the first time. The results show that most bears can flexibly adapt their diet to climate and food availability, thereby shifting their ecological role. In the new study, published in the journal “Nature Communications,” the researchers propose that the changing role large omnivores play can strengthen the resilience of ecosystems to global environmental changes.
Berries, roots, nuts, and grasses, but also insects, fish, and mammals – bears can have a highly diverse diet. The composition of their food varies greatly, depending on the species and the season. In summer and fall, for example, brown bears predominantly feed on berries or nuts, while their diet in spring contains more meat. This adaptability makes bears successful survivors in various regions of the world, from the Arctic tundra to dense tropical forests. “Omnivores can play a dynamic and stabilizing role in ecosystems when environmental conditions change. Although they exist in almost all habitats and on all levels of the food web, we still know surprisingly little about their response to changes in their ecosystems,” explains Dr. Jörg Albrecht from the Senckenberg Biodiversity and Climate Research Center Frankfurt.
Together with an international research team involving 18 scientists from Europe and Canada, Albrecht compiled extensive ecological and paleoecological data on seven bear species – the largest terrestrial carnivores – for the first time. “Unlike most other large carnivores, bears tend to prefer a low-protein diet and most bear species possess fewer anatomical and physiological adaptations to meat consumption. This flexibility enables them to have an exceptionally varied diet,” explains the Senckenberg researcher, and he continues “This means that bears take on many ecological roles at the same time: they hunt prey, eat carrion, disperse seeds, and feed on plants. In this way, they affect prey populations, the growth and distribution of plants, nutrient cycling, and energy flows, both in terrestrial and aquatic ecosystems.”
By combining macroecological and paleoecological methods, the researchers were able to show that most bear species are able to flexibly adapt their position in the food web to the availability of resources and the climate. In regions with low food availability and short growing seasons, they have a more carnivorous diet, whereas in productive areas with long growing seasons, they prefer plant-based foods. “Our isotope analyses of fossil bones from the late Pleistocene and Holocene also show that the European brown bear progressively switched to a plant-based diet in the course of increasing primary production and longer vegetation periods following the last ice age around 12,000 years ago,” adds coauthor Prof. Dr. Hervé Bocherens from the Senckenberg Centre for Human Evolution and Palaeoenvironment at the University of Tübingen.
The study highlights the value of natural history collections for research on global environmental change. The team analyzed bone material from brown bears and red deer housed in 14 natural history and paleontological collections across Europe. Red deer were included because they eat only plants, providing a clear reference point for determining whether brown bears feed lower or higher in the food web. “Working with the collection objects is like detective work: isotope analyses provide a window into the past, allowing us to reconstruct what these animals ate thousands of years ago during the last Ice Age—a time when the world was very different from today,” says senior author Prof. Dr. Nuria Selva from the Doñana Biological Station (CSIC) in Spain and the Institute of Nature Conservation of the Polish Academy of Sciences (PAN).
The results show a connection that has so far received little attention: large omnivores change their role in the ecosystem – the research team refers to this as “trophic rewiring”. “Our results highlight the crucial role that omnivorous megafauna—many of which are also large carnivores—play in ecosystems. They can help to ensure that food webs remain stable despite global pressures such as climate change. In this way, large carnivores contribute to ecosystem resilience and stability, which is essential in a rapidly changing world” says Selva.
“Global environmental change is fundamentally altering the structure of food webs on land and in the water – often with drastic consequences for entire ecosystems. Large omnivores at the top of the food web are of particular interest here. They use a wide range of food sources, are highly adaptable, and often respond quickly to environmental changes. If their role in the ecosystem shifts – e.g., from predators to herbivores – this can change the structure of entire food webs. The way omnivores respond to environmental changes could therefore be an early warning signal of profound upheavals in ecosystems,” adds Albrecht in summary.
Publication: Albrecht, J., Bocherens, H., Hobson, K.A. […] & Selva, N. (2025) Dynamic omnivory shapes the functional role of large carnivores under global change. Nature Communications 16:10896. https://doi.org/10.1038/s41467-025-65959-7
Berries, roots, nuts, and grasses, but also insects, fish, and mammals – bears can have a highly diverse diet. The composition of their food varies greatly, depending on the species and the season. In summer and fall, for example, brown bears predominantly feed on berries or nuts, while their diet in spring contains more meat. This adaptability makes bears successful survivors in various regions of the world, from the Arctic tundra to dense tropical forests. “Omnivores can play a dynamic and stabilizing role in ecosystems when environmental conditions change. Although they exist in almost all habitats and on all levels of the food web, we still know surprisingly little about their response to changes in their ecosystems,” explains Dr. Jörg Albrecht from the Senckenberg Biodiversity and Climate Research Center Frankfurt.
Together with an international research team involving 18 scientists from Europe and Canada, Albrecht compiled extensive ecological and paleoecological data on seven bear species – the largest terrestrial carnivores – for the first time. “Unlike most other large carnivores, bears tend to prefer a low-protein diet and most bear species possess fewer anatomical and physiological adaptations to meat consumption. This flexibility enables them to have an exceptionally varied diet,” explains the Senckenberg researcher, and he continues “This means that bears take on many ecological roles at the same time: they hunt prey, eat carrion, disperse seeds, and feed on plants. In this way, they affect prey populations, the growth and distribution of plants, nutrient cycling, and energy flows, both in terrestrial and aquatic ecosystems.”
By combining macroecological and paleoecological methods, the researchers were able to show that most bear species are able to flexibly adapt their position in the food web to the availability of resources and the climate. In regions with low food availability and short growing seasons, they have a more carnivorous diet, whereas in productive areas with long growing seasons, they prefer plant-based foods. “Our isotope analyses of fossil bones from the late Pleistocene and Holocene also show that the European brown bear progressively switched to a plant-based diet in the course of increasing primary production and longer vegetation periods following the last ice age around 12,000 years ago,” adds coauthor Prof. Dr. Hervé Bocherens from the Senckenberg Centre for Human Evolution and Palaeoenvironment at the University of Tübingen.
The study highlights the value of natural history collections for research on global environmental change. The team analyzed bone material from brown bears and red deer housed in 14 natural history and paleontological collections across Europe. Red deer were included because they eat only plants, providing a clear reference point for determining whether brown bears feed lower or higher in the food web. “Working with the collection objects is like detective work: isotope analyses provide a window into the past, allowing us to reconstruct what these animals ate thousands of years ago during the last Ice Age—a time when the world was very different from today,” says senior author Prof. Dr. Nuria Selva from the Doñana Biological Station (CSIC) in Spain and the Institute of Nature Conservation of the Polish Academy of Sciences (PAN).
The results show a connection that has so far received little attention: large omnivores change their role in the ecosystem – the research team refers to this as “trophic rewiring”. “Our results highlight the crucial role that omnivorous megafauna—many of which are also large carnivores—play in ecosystems. They can help to ensure that food webs remain stable despite global pressures such as climate change. In this way, large carnivores contribute to ecosystem resilience and stability, which is essential in a rapidly changing world” says Selva.
“Global environmental change is fundamentally altering the structure of food webs on land and in the water – often with drastic consequences for entire ecosystems. Large omnivores at the top of the food web are of particular interest here. They use a wide range of food sources, are highly adaptable, and often respond quickly to environmental changes. If their role in the ecosystem shifts – e.g., from predators to herbivores – this can change the structure of entire food webs. The way omnivores respond to environmental changes could therefore be an early warning signal of profound upheavals in ecosystems,” adds Albrecht in summary.
Publication: Albrecht, J., Bocherens, H., Hobson, K.A. […] & Selva, N. (2025) Dynamic omnivory shapes the functional role of large carnivores under global change. Nature Communications 16:10896. https://doi.org/10.1038/s41467-025-65959-7
