Climate change intensifies intraguild interactions between top predators and creates a new potential evolutionary pathway

Adaptations of coexisting species to climate-driven environmental changes might not necessarily lead to extinctions, but rather to trait variations that generate new competitive hierarchies in ecosystems. Top predators have a pivotal role as indicators or even generators of high biodiversity in ecosystems, but effects of climate change on top predators have not been sufficiently explored. We used long-term data on the territory and breeding dynamics of two coexisting, ecologically similar and closely related forest raptors, the temperate zone Tawny Owl (Strix aluco) and the boreal zone Ural Owl (S. uralensis), in an area that has experienced significant climate change (>1°C mean temperature increase) but not habitat change in the last 20 years. We analysed long-term population dynamics of both species along an altitudinal gradient by measuring changes in territory overlap and nest displacement rate as well as effects on species breeding productivity and body size. As a result of concurrent population growth and range expansion, we observed a gradual intensification of competition for space and nest sites, including direct nest displacement of the smaller Tawny Owl by the larger Ural Owl. We observed that breeding Ural Owl females became significantly larger in shared territories with Tawny Owls compared to those in unshared territories. From an evolutionary-ecological perspective, this size disparity could bolster the Ural Owl’s dominance over the Tawny Owl. However, it could also pose long-term risks for the Ural Owl, as the advantages of larger size come with increased energy demands and reduced hunting agility. This study highlights that, beyond theoretical model predictions, robust long-term monitoring data are urgently needed to capture the actual changes taking place due to the effects of global warming and to reveal the hidden and trait-based adaptations of coexisting species and unforeseen drivers of extinction.