Charaxes Butterflies as Bioindicators of Forest Integrity: Conservation Priorities for Kenya's Threatened Nandi Forests

Abstract

Fragmented tropical forests urgently need practical, cost-effective tools to assess ecosystem health and direct management resources where they matter most. Butterflies of the genus Charaxes are promising candidates: their larvae depend on specific woody host plants, and adults are readily sampled using fruit-baited traps, linking assemblage patterns directly to forest structure and quality. We assessed Charaxes diversity, disturbance responses and habitat associations across North Nandi Forest (~11,000 ha; 1700–2130 m a.s.l.) and South Nandi Forest (~15,000 ha; 1600–2000 m a.s.l.), two of Kenya's last Guineo-Congolian rainforest fragments. Six sites spanning a disturbance gradient were sampled monthly throughout 2023, with Van Someren-Rydon fruit-baited traps and visual censuses deployed concurrently at all sites to ensure comparability. A total of 1847 individual Charaxes belonging to 18 species were recorded. Both forests maintained high diversity (Shannon H′ = 2.61–2.64; Pielou's J′ > 0.91) and log-normal rank-abundance distributions, confirming intact community structure. Species inventories were near-complete (Chao1: 90%–95%). Total Charaxes abundance declined by 61% from intact to heavily disturbed sites (Kruskal–Wallis H(2) = 14.32, p = 0.001, η2 = 0.72), with three forest specialists, Charaxes cithaeron, C. violetta and C. zoolina, declining by 72%–76% and showing strong fidelity to closed-canopy habitats (79%–84% of captures under shade). Canonical correspondence analysis explained 52.3% of species–environment variation (F (5,6) = 3.14, p = 0.002, 999 permutations), with Prunus africana density (r = 0.68), canopy cover (r = 0.64) and host plant richness (r = 0.61) as the strongest predictors. Bioindicator evaluation using IndVal analysis identified four robust candidate species (IndVal 68.7–76.3, p < 0.005), and significant compositional turnover between forest blocks (βSIM = 0.38) confirmed that each contributes uniquely to regional diversity. Based on these findings, we recommend equal conservation investment in both forests, maintaining canopy cover above 70%, targeted protection and enrichment planting of P. africana and Turraea stapfiana, and a tiered monitoring protocol using the three specialist species as early-warning bioindicators of forest deterioration.