Brown bear (Ursus arctos) feeding on fruit in a mixed forest. Credit: Vincenzo Penteriani.
Climate change and interactions between species are changing the distribution of brown bears in Europe.
Trophic relationships are key to understanding changes in the distribution of certain species, according to a new study involving experts from 26 countries
An international team led by the University of Seville, La Sapienza University of Rome and the Institute of Nature Conservation in Poland has studied how interactions between species affect the distribution of brown bears in Europe and Turkey.
It has been found that the distribution of bears on a continental scale is largely explained by interaction with other species: specifically, bears occupy areas where the species that form part of their diet are distributed.
The research shows the importance of interactions between species on a continental scale, using the brown bear as a case study.
Critical
Understanding how global changes – such as climate change or land use transformation – affect species is critical to conserving biodiversity and maintaining the benefits that nature provides, such as clean water, soil fertility and pollination.
For example, as a result of climate change, the distribution of some species is shifting to higher altitudes or towards the poles, where climatic conditions remain within the species’ tolerances.
Until now, most studies have focused only on the importance of direct changes, such as changes in temperature, rainfall or agricultural use, on species distributions.
However, this work has turned the spotlight on indirect effects through interactions between species.
US researcher Pablo M Lucas said: “The bears showed a very varied diet: we detected 276 species in their diet.
“Bears living in warmer places, such as sub-populations in the Cantabrian Mountains, Greece or Turkey, have a more vegetarian diet, while in colder areas such as Scandinavia and Finland, bears are more carnivorous.
“This means that the role of bears in the ecosystem/ food chain is different, varying between herbivore and apex predator.”
He added: “Thanks to our large international team, we had more than three million bear locations, corresponding to some 3,000 bears and, very importantly, data from the 14 European and Turkish sub-populations, which inhabit very different environments.
“This allowed us to study the effects of local interactions over a continental area. We observed that bears occupy those places where the most energy from the species in their diet is available.
“For example, in the Cantabrian Mountains, the presence of oak and beech trees, which are the main food source for this sub-population, makes the presence of bears more likely; in other sub-populations where bears are more carnivorous, the presence of bears is better explained by the distribution of wild ungulates such as wild boar and deer.”
Protecting species
This information is particularly important for predicting where species will live in the future and what roles they play in ecosystems, in a context of climate change and land use transformation, and for understanding that in order to protect species, we must conserve the ecosystems where they live.
Lucas said: “Changes in the distribution of the species they feed on may affect the bear’s position in the food chain and the viability of the species at the local level.”
Other species with characteristics different from those of brown bears – such as a more specialised diet, less ability to move, or the ability to live only in very specific environmental conditions – may react differently to climate change, land use transformation, and changes in the species with which they interact.
Improving this knowledge is essential for designing more effective strategies for conserving biodiversity and the services that nature provides us.
The study is published in the journal Global Change Biology.
