Climatic refugia of a warm-adapted bird during the Late Quaternary: Insights from species distribution modeling in Southwest Asia

Quaternary climatic fluctuations have played a major role in shaping species distributions, particularly for taxa adapted to warm and semi-arid environments. In this study, we reconstructed the distribution of the White-eared Bulbul (Pycnonotus leucotis) across Southwest Asia to identify potential climatic refugia and examine range dynamics during the Late Quaternary. Species occurrence records (n = 384) and bioclimatic variables from WorldClim were integrated using the Maximum Entropy (MaxEnt) algorithm to model habitat suitability under current conditions, the Last Glacial Maximum (LGM, ~21 ka), and the mid-Holocene (MH, ~6 ka). Model performance was satisfactory to high (AUC = 0.87-0.96), indicating good discriminatory ability between suitable and unsuitable habitats. The results revealed pronounced shifts in the spatial distribution of suitable habitats in response to climatic oscillations. During the LGM, the spatial configuration of suitable habitats shifted toward several refugial regions, including the Persian Gulf basin, the western slopes of the Zagros Mountains, Mesopotamia, and areas between the Indus River and the Himalayan range. In contrast, habitat suitability expanded markedly during the MH, reaching approximately 8.67 million km² compared with 4.95 million km² under current conditions. Across all periods, species distribution was strongly influenced by temperature-related variables, particularly bio10 (mean temperature of the warmest quarter) and bio11 (mean temperature of the coldest quarter), highlighting the importance of thermal constraints in shaping the ecological niche of the species. The exposure of the Persian Gulf basin during periods of lower sea level may have created additional suitable habitats, emphasizing its potential role as a climatic refugium for warm-adapted species. Overlay analyses revealed three distinct categories of refugial dynamics, including constant refugia, LGM-specific refugia, and post-glacial expansion areas. These findings highlight the importance of Southwest Asia as a refugial system and provide insights into the processes that have shaped regional biodiversity under past climatic change.