Extinction in the north and colonisation in the south: the latitudinal drivers of community warming.

As the climate warms, species are shifting their ranges to match their climatic niches, leading to the warming of ecological communities (thermophilisation). We currently have little understanding of the population-level processes driving this community-level warming, particularly at rapidly warming high latitudes. Using 30 years of high-resolution moth monitoring data across a 1,200 km latitudinal gradient in Finland, we found that higher latitude communities are experiencing more rapid thermophilisation. We attribute this spatial variation to community-wide colonisation-extinction dynamics, both for the full community and for different thermal affinity groups. Our findings reveal that latitudinal variation in the pathways underpinning thermophilisation is the net outcome of opposite forces: in the north, community warming is driven by the extinction of cold-affiliated species, while in the south, it is driven by high colonisation rates of warm-affiliated species. Thus, we show how species' thermal affinities influence community reorganisation and highlight the elevated extinction risk among cold-affiliated species.