Altitude-mediated niche partitioning between Dacus bivittatus and Dacus punctatifrons along an elevational transect in the Uluguru Mountains, Tanzania

Understanding how fruit fly species partition resources along environmental gradients is important for predicting pest pressure under changing climatic conditions. The population ecology of Dacus bivittatus (Bigot) and Dacus punctatifrons (Karsch) (Diptera: Tephritidae) was examined across six sites spanning 526–1,650 m above sea level in the Uluguru Mountains, Tanzania, over eight years (2004–2012). A total of 2,200 weekly trap records were aggregated into 292 site-month observations and standardised as flies per trap per day (FTD). Dacus bivittatus showed strong seasonal structuring (H = 43.03, p < 0.001), with abundance peaking during the cool dry season (June–August), whereas D. punctatifrons showed no clear seasonal pattern. Both species declined significantly with increasing altitude (ρ = −0.308 and −0.769, respectively; p < 0.001), but the decline was steeper for D. punctatifrons . Species dominance shifted along the gradient: D. punctatifrons dominated warm lowland conditions (>24 °C), whereas D. bivittatus prevailed at elevations above approximately 569 m. Seasonal niche overlap declined markedly with altitude, indicating increasing temporal segregation between the species in cooler environments. These findings demonstrate that altitude structures ecological divergence between two closely related fruit fly pests and provide a basis for site-specific monitoring and climate-sensitive pest forecasting in tropical mountain agroecosystems.