Ecological Filters Shape Community Thermophilisation Under Climate Change

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ABSTRACT Aim Climate warming is increasingly associated with shifts in community composition, yet the pace and drivers of these changes remain unclear. Location Germany. Time Period 2005–2024. Major Taxa Studied Birds. Methods Using structured time‐series data from a large, countrywide Common Bird Monitoring scheme, we quantified community‐level thermophilisation, that is, the shift in community composition toward warm‐affinity species. We investigated potential thermophilisation drivers integrating ecological, life‐history, and demographic processes using generalized additive models (GAMs). Results Over 57% of the analysed communities exhibited thermophilisation, at a median rate of 0.003°C/yr. −1 , lagging behind local temperature increases. Rates and trajectories were strongly influenced by habitat, trophic guild, and demographic processes. Forest, open‐habitat, and wetland assemblages tracked warming faster than urban or farmland communities. Colonization of warm‐affinity species and extinction of cold‐affinity species emerged as key mechanisms driving change. High baseline diversity negatively related to the rates of thermophilisation. Our results highlight that thermophilisation is shaped not only by temperature rise, but by the interaction of climate change, ecological filtering, and demographic processes. Conclusions Our study underscores that community responses are influenced as much by landscape context, habitat structure and colonization/extinction dynamics as by warming itself. This emphasizes the need to conserve species‐rich assemblages, protect cold‐affinity taxa and maintain habitat connectivity. It also suggests that areas offering species shelter from extreme heat while providing cooler microhabitats need to be maintained under climate change.