Phenological plasticity alters community structures of mountain Lepidoptera

The current increase in annual temperatures is altering the spatial distribution and timing of activity patterns, i.e. phenology, of many animal and plant species. Theory predicts such phenological plasticity to affect community composition and food web structure. We inferred temporal changes in Lepidoptera phenology in a mountainous region of northern Austria characterised by ongoing environmental and climate change. Long-term records (1960‒2022) representing 189,993 records of 2111 Lepidoptera species at two elevational belts served to assess phenology and species composition at a weekly resolution. Temporal trends towards earlier appearance in spring and prolonged activity in autumn altered short-term community composition at lower and higher elevations. Phenological plasticity was high throughout the study period and increased over the course of the years, becoming more and more fuzzy towards autumn. Variability in community composition decreased over the years. We found little evidence for synchronous phenological shifts at the community level. Species-specific phenological plasticity seems to prevail, causing constant changes in seasonal community composition. Long-term directional changes in community composition due to increasing temperature might change food webs and affect species interactions, particularly pollination, and possibly insect and plant diversity.