Bears can survive in a wide variety of habitats. Because they are basically omnivores, they adapt their diet flexibly to the available food supply. This applies not only to regional conditions, but also to epochal environmental changes such as those currently associated with climate change, as a new study shows. The versatile bears thereby indirectly strengthen the ecosystems in their habitats and make them more resilient to climate change.
The diet of the various bear species includes berries, roots, nuts and grasses, but also insects, fish and mammals. What exactly the predators eat depends on the season and the species. For example, the brown bear eats mainly berries or nuts in summer and autumn and more meat in spring. Depending on what is available, all bear species adapt their diet flexibly. This allows them to survive in a wide variety of regions of the world, from arctic tundras to dense tropical forests. But conversely, how do these omnivores affect their habitats? How do environmental changes caused by climate change affect ecosystems and what role does bears play as the largest land-living predators at the top of the food chain?
Interactions between bears and their habitat
A research team led by Jörg Albrecht from the Senckenberg Biodiversity and Climate Research Center Frankfurt has now investigated this. To do this, the biologists evaluated ecological and paleoecological data on seven species: European brown bear, American black bear, Andean bear, Asiatic black bear, Sun bear, panda bear and sloth bear. In particular, they compared data on the composition of the animals’ feces and stomach contents, which had been examined in previous studies.
The evaluation showed that bears’ anatomy and metabolism are not limited to meat. In fact, they prefer a relatively low-protein and exceptionally varied diet compared to other large predators. “This means that bears take on many ecological roles at the same time: they hunt prey, eat carrion, spread seeds and feed on plants,” reports Albrecht. “In this way, they influence prey populations, plant growth and distribution, nutrient cycling and energy flow – in both terrestrial and aquatic ecosystems.”
Most bear species not only adapt their diet flexibly to the available resources, but also to the prevailing climate, as the team found. In cold or dry regions and periods with short growing seasons they eat a more meat-based diet; in warmer or wetter regions and periods with long growing seasons they prefer plant-based food. An extreme example of this is the panda, which has adapted to its habitat in the humid mountain forests of China and now eats almost exclusively bamboo. However, meat-vegetable variability applies equally to bears today and to bears in the past, as analyzes of fossil bones and teeth have revealed. “The European brown bear increasingly switched to plant-based food as a result of increasing primary production and longer vegetation periods after the last ice age around 12,000 years ago,” reports co-author Hervé Bocherens from the University of Tübingen.
Bears stabilize food webs
The results demonstrate a connection that has previously received little attention: large omnivores such as bears change their role in the ecosystem when necessary. “They can help food webs remain stable despite global environmental changes such as climate change. In this way, large carnivores contribute to the resilience and stability of ecosystems, which is crucial in a rapidly changing world,” says senior author Nuria Selva from the Polish Academy of Sciences.
The current climate change is once again changing the food webs on land and in water – with sometimes drastic consequences for entire ecosystems, the team emphasizes. Because large omnivores such as bears use a wide range of food sources and adapt quickly to environmental changes, they have an important role to play in this ecological upheaval caused by global warming. “If their role in the ecosystem shifts – for example from predators to herbivores – this can change the structure of entire food webs,” says Albrecht. “The way omnivores respond to environmental changes could therefore be a sensitive early indicator of profound shifts in ecosystems.”
Source: Senckenberg Society for Natural Research; Specialist article: Nature Communications, doi: 10.1038/s41467-025-65959-7