Anthropogenic Niche Truncation: Three Millennia of Range Contraction and Future Conservation Implications for Chinese Megafauna Reptiles

The relative impacts of climate change versus human activities on Quaternary megafaunal distribution and extinction remain debated. To address this, we developed an innovative spatiotemporal framework integrating historical anthropogenic and climatic data from 1046BCE to 1950CE. Employing an ENMeval-optimized MaxEnt model, we quantified the distributional evolution of four megafauna reptiles in China (Pelochelys cantorii, Alligator sinensis, Python bivittatus, and Hanyusuchus sinensis) over the past three millennia. We further projected future habitats for three extant species (P. cantorii, A. sinensis, P. bivittatus) under different emission scenarios. Results indicate that, while climatic fluctuations established the foundational distribution framework, human activities drove the historical decline through continuous physical truncation of climatic niches. The dominant anthropogenic stressor transitioned from early agricultural expansion to late historical demographic explosions. This transition culminated in massive habitat loss and extinctions, while forcing extant species to passively retreat into fragmented topographical microrefugia. Under different future climate scenarios, species responses exhibit stark polarization. Sensitive species experience extreme area fluctuations tightly linked to emission pathways, whereas others remain locked in spatial dead ends. Modern anthropogenic landscapes form insurmountable physical barriers that cause dispersal limitations. Consequently, conservation strategies in the Anthropocene necessitate a fundamental transition from traditional in situ protection to proactive interventions that integrate emission reductions with assisted migration.