Authors: Marjakangas, Emma-liina; Santangeli, Andrea;Lehikoinen, Aleksi;

Climate change affects ecological communities via their species. The community’s response to climate change can be represented as the temporal trend in a climate-related functional property that is quantified using a relevant functional trait. However, some species influence this response more strongly than others. Following a general definition of a keystone species, species that have a strong effect on the community’s functional response to climate change beyond their relative abundance can be considered as ‘climate keystone species’. We develop a stepwise tool to determine the species’ effects on the community-level response to climate change and identify climate keystone species. We quantify the difference between community’s climate change responses including and excluding the species of interest to obtain the species-specific effect on the community’s response. Then, we identify as climate keystone species those species with a strong residual effect after weighting with their relative abundances in the community. To illustrate the use of the stepwise tool with empirical data, we identify climate keystone species that have a strong effect on the change in the average temperature niche in North American bird communities over time. Identification of climate keystone species can serve as an additional conservation method to protect ecosystem functions efficiently.