Spatial and Temporal Distribution Patterns of High-Altitude Butterflies in the Eastern Himalayan Landscape of West Bengal, India

Mountains are considered to be natural laboratories for experimenting ecological and evolutionary responses of organisms to environment. Spatial distribution of species is shaped by habitat heterogeneity and environmental gradients dependant on elevation. Higher altitude with their unique cloud cover and microclimate sustain specialized montane species. However temporal pattern in butterfly distribution is largely driven by resource utilization. Entire study was designed to document the distribution of high altitude butterflies in the Eastern Himalayan landscape of West Bengal, India between January to December 2025. Determination of diversity (Shannon Index “H´”), evenness (Pielou Index “E”, Equitability Index “Eq”), richness (Menhinick Index “R1”, Margalef Index “R2”) and dominance (Berger-Parker Dominance “DBP”) across five altitudinal belts (≤2500 masl; 2501-3000 masl; 3001-3500 masl; 3501-4000 masl; ˃=4001 masl) was done. Additionally, temporal shift in butterfly distribution across the similar study site was explored. Highest number of species (51) and maximum number of individuals (1365) was observed at 2500-3000 masl while July recorded the greatest number of species (50) and individuals (734). Species diversity increased from ≤2500 masl (H´=5.564) to 2500-3000 masl (H´=5.580) followed by a monotonical decline with increasing elevation. Species richness was highest at ≤2500 masl (R1=1.497; R2=6.983) leading to subsequent decline with elevation. Homogenous species distribution with high evenness at ≤2500 masl (E=0.986; Eq=0.9859) leading to a steady decline was also recorded. Interestingly species dominance was greatest at ˃=4001 masl (DBP=0.1394). Monthly variation in species diversity, richness, evenness and dominance reflected temporal variability in species occurrence. Mid-elevation peak in species diversity (H´=5.587) and species richness (R1=1.846; R2=7.426) was observed in July. January was marked by high evenness (E=0.992; Eq=0.9913) in species distribution. Floral resource is more prevalent during rainy months (June-July) which probably translated with higher number of species through time across elevation. Progressive decline in their distribution could be due to stricter environmental constraints and resource.