Can omnivores be considered keystone species? Bears as a study case

Abstract

Abstract The functional roles of herbivores and carnivores in ecosystems have been relatively well studied: both can shape ecosystems through strong direct and indirect top‐down controls on other guilds. By contrast, the role omnivores play has been rarely explored, even though their diet spans several trophic levels and potentially has numerous effects on ecosystems through trophic and non‐trophic interactions. To gain a better understanding of the potential ecosystemic role of omnivore trophic and non‐trophic interactions, we performed a literature review on bears (Ursidae): a specific group of terrestrial omnivores. We submitted equation searches on the Web of Science for each type of interaction and omnivorous bear species. We kept 411 references highlighting a wide range of trophic and non‐trophic interactions in various ecosystems. Our review sheds light on the large number, diversity, and significance of these interactions. Moreover, we highlight a great variability of interactions among bear species but also across ecosystems for a given bear species. Beyond bears, our review shows that omnivores play a pivotal role in ecosystem functioning, not only through the strong interactions they have with a reduced set of other species but also through multiple weaker interactions with a diversity of taxa at different trophic levels. We therefore suggest that omnivores can be considered keystone species, and in any case, are worthwhile conservation targets, even though further studies are needed.

The authors' abstract, as published at the source. Ecosphere, 2026 · DOI ↗