Vegetation determines butterfly diversity and composition across the Arabuko-Sokoke coastal forest in Kenya, a tropical biodiversity hotspot

Community structures, including butterfly diversity, are shaped by both biotic and abiotic factors, with forest type exerting a significant influence. The Arabuko Sokoke Forest (ASF), the largest remaining coastal forest fragment in Kenya and East Africa, is rich in biodiversity and endemic species. Given its varied forest types, ASF provides a unique opportunity to examine how these differences affect butterfly community structure. This study aims to investigate how vegetation diversity and structure influence butterfly community structures and species richness within ASF. We conducted butterfly and woody plant surveys during the dry season across four distinct forest types in ASF: Cynometra forest, Brachystegia woodland, mixed forest and the forest edge. Butterfly populations were sampled using transects measuring 10 m × 100 m and woody plant species were surveyed along overlapping transects. A total of 6,050 butterfly individuals were recorded, representing 86 species across 38 genera and five families. The woody vegetation comprised 178 species, belonging to 78 genera and 34 families. Significant differences in butterfly species abundance were observed across the forest types, though no significant differences were found in species richness. Beta diversity analyses revealed consistently high community dissimilarity across all forest types, driven predominantly by balanced variation in species abundances rather than nestedness. Brachystegia forest exhibited the highest total beta diversity, while forest edge exhibited the lowest. This indicates that species turnover, rather than richness differences, is the primary mechanism structuring butterfly communities at the landscape scale in Arabuko Sokoke Forest. Butterfly species diversity showed a strong correlation with plant species diversity. Additionally, butterfly wingspan size varied significantly amongst forest types. Our findings underscore the crucial role of natural plant forest diversity in supporting butterfly diversity and highlight the synergistic functions of the mixed forest and Brachystegia forest as key habitats. There is need for conservation strategies that account for multiple dimensions of biodiversity. While mixed forest serves as a reservoir of high species richness and abundance, Brachystegia forest offers critical value through their contribution to beta diversity at the landscape level. These results highlight the fundamental importance of conservation efforts directed to protect high plant diversity and structural heterogeneity to provide a broad spectrum of ecological niches and habitat connectivity for butterflies. Such strategies will enhance butterfly diversity and contribute to effective conservation in fragmented forests and especially in Arabuko Sokoke Forest.