Habitat configuration and habitat quality shape butterfly diversity in tropical dry coastal forests of southern Kenya

The conversion of natural habitats into agricultural and urban areas has led to habitat loss and respective fragmentation as well as decline in habitat quality within the remaining natural habitat patches. Today, this negative trend is particularly pronounced in tropical forest ecosystems. For instance, the formerly continuous East African coastal forest has shrunk over time to relatively few, mostly small forest patches of varying size, isolation, and habitat quality. In this study, we analyse butterfly responses to environmental change and habitat disturbance across selected coastal forest patches in southern Kenya, including protected forest and sacred Kaya forests. We surveyed butterflies in nine forest remnants along the Kenyan coast from the years 2022 to 2025 based on transect counts and bait traps. We recorded a total of 4,893 butterflies representing 187 species. Species richness differed significantly among forests. Butterfly diversity, but not abundance, was highest in the largest forest area, i.e. the Arabuko Sokoke forest (107 species), while seven small Kaya fragments exhibited reduced species numbers (max. 70 species), with lowest number in Kaya Kambe and Shimba Hills. However, total Kaya richness was considerably higher (167 species) than that of the much larger and largely intact Arabuko Sokoke and Shimba Hills forests combined (111 species). Species turnover was high, with 12.4% average species overlap among forest fragments, 37.4% of species restricted to a single forest, and only eight species occurring in all sites. Habitat quality had a significant effect on species diversity and assemblage composition, with a marked decline in species diversity in the most degraded forest fragments. Community trait composition was dominated by widespread generalist species, but forest-dependent specialist species comprised 40% of all recorded species. Such typical forest species were also found in the small Kaya forest patches. In conclusion, our study underlines that large and protected forest blocks represent high butterfly diversity, but also the small Kaya forests appeared to be crucial for conserving overall butterfly diversity of Kenya’s coastal region.