Ignoring biotic interactions overestimates climate change effects: The potential response of the spotted nutcracker to changes in climate and resource plants

AIM: Projecting future distributions of species under climate change remains a particular challenge for species that are trophically interacting. Interaction partners are often assumed to react differently to climate change, causing spatial mismatches in future distributions and increased extinction risks. We compare potential direct effects of climate change with combined direct and indirect effects mediated via food plants on a highly specialized bird species. LOCATION: Europe. TAXON: European spotted nutcracker (Nucifraga caryocatactes). METHODS: We used climate‐based species distribution models to project probabilities of occurrence of European spotted nutcrackers and their main food sources, Swiss stone pine (Pinus cembra) and common hazel (Corylus avellana) under climate change. We combined direct climate change effects on the bird and indirect effects via the food plants by calculating the probabilities of plants and nutcrackers occurring together. RESULTS: We find considerable projected northward shifts in future occurrences of nutcrackers under climate change and similar effects on hazel. In contrast, projections for Swiss stone pine indicate minor altitudinal upward shifts. Combined projections of direct and indirect effects of climate change indicate less pronounced shifts of nutcrackers’ occurrences, due to relatively small changes in pine's occurrences and to suitable hazel occurrence shifts. MAIN CONCLUSIONS: Our study suggests that potential effects of climate change on the future distribution of the nutcracker might be overestimated when ignoring trophically interacting plants in future projections. Models of direct effects of climate change on nutcrackers’ occurrence probabilities project greater range losses than models of combined direct and indirect effects via resource plants. Therefore, considering biotic interactions does not necessarily increase the risks that climate change may impose on species distributions, but could reduce overestimation of potential range losses in rapidly changing environments.