Declines and variation in butterfly species richness and community composition in a montane protected area after 35 years

Climate change is expected to impact species composition and distribution, and insects may be particularly affected given their short lifecycles. To examine climate associated changes in a montane butterfly community, butterfly species richness and community composition in 21 butterfly monitoring sites arrayed along elevation and varying habitat types were assessed in two temporal snapshots 35 years apart. Butterfly data from past (1988–1989) and present (2022–2023) surveys were compared. Changes in site-related annual and seasonal cumulative growing degree days (cGDD), a measure of thermal accumulation, over 35 years were assessed with Mann-Kendall trend tests. Generalized linear mixed effects models (GLMM) were used to test for changes in species richness between past and present at the park-wide scale, along an elevation gradient, and among habitat types. Temporal beta diversity indices were used to test for species composition changes. Thermal accumulation increased over the 35-year period for all ten alpine and high alpine sites, and for four or six additional sites, using annual or summer data, respectively. Overall species richness was 18% less in the present study compared to the past, although there was interannual variation within study periods. Changes along the elevation gradient or among habitat types were not found. Butterfly community composition differed between studies, and the total dissimilarity in community composition was dominated by species losses. Implications for conservation There were decreases in butterfly richness and increases in cGDD over time, but there were no shifts along the elevation gradient or among habitat types, indicating no habitat-specific reaction to warming temperatures. Changes, in combination with variation among study years within these two temporal windows, warrants continued monitoring of this butterfly community.