Food Plant Availability Constrains Climatic Niches of Host‐Specialized Europe‐Centred Butterflies

ABSTRACT Aim Evaluating whether host plants can constrain the current distribution of host‐specialized butterflies as well as their ability to adapt ranges to climate change at cold and warm range margins. Location Continental Europe. Time Period Current to end of 21st century. Major Taxa Studied Butterflies. Methods We determined thermal niche margins of host‐specialized, Europe‐centred butterflies and their hosts from occurrence records and defined butterflies as potentially range‐limited by hosts if these limits differed by ≤ 0.1°C, ≤ 1°C or ≤ 2°C between the butterfly and its host collective. We used future temperatures under mild and pronounced climate change scenarios to evaluate whether a static host distribution could constrain butterflies' range adaptations at the cold margin or trigger co‐extinctions at the warm margin. Finally, we assessed relations between current host limitations and range size, mobility, phylogenetic host‐niche breadth, and red‐list status of the butterflies. Results Of the 118 butterfly species studied, 48/33 (cold/warm margin) were potentially host‐limited, when using the ≤ 2°C as criterion, 29/11 species under the ≤ 1°C criterion, but only 15/5 species using the ≤ 0.1°C criterion. Expansion at the cold margin was potentially hampered by host immobility in 22 and 59 species under mild and pronounced climate change, respectively, while we detected risk of co‐extinction at the warm range margin in 14 and 55 species. Current host limitation at the cold margin increased with larger butterfly ranges. No consistent relations with other variables were detected. Main Conclusions The distribution of several specialized Europe‐centred butterflies is at least co‐constrained by their hosts already today, and the impact of these constraints may intensify in the future. This is not only true at cold, but also at warm range limits, implying a risk of yet understudied future co‐extinctions. Understanding and prediction of climate‐change effects on insects thus need increased consideration of simultaneous host plant dynamics.