Threshold Responses of Bird Communities to Human Footprint: Testing the Intermediate Disturbance Hypothesis and Implications for Biodiversity Conservation.

Human activities have profoundly altered natural ecosystems, driving widespread biodiversity declines. Birds serve as key environmental health indicators and exhibit high sensitivity to such changes. The Human Footprint Index (HFP) quantifies cumulative anthropogenic pressure, providing a robust framework to assess ecological responses to disturbance. We quantified species-specific and community-level thresholds in bird communities along an HFP gradient in northeastern Inner Mongolia using Threshold Indicator Taxa Analysis (TITAN). Using piecewise regression, we analyzed HFP-driven changes in species richness and Shannon diversity to test the Intermediate Disturbance Hypothesis (IDH)-predicting peak biodiversity at intermediate disturbance levels. Our results reveal a community threshold at HFP around 14, indicating a shift in community composition, with species-specific thresholds ranging from 3.37 to 43.22. Species richness and Shannon diversity peak at intermediate HFP levels (around 23.5), supporting the IDH, but decline at higher levels. These findings highlight the complex interplay between human impact and biodiversity, emphasizing the need for conservation strategies that consider both community composition and overall diversity, whereas addressing potential extinction debts and the roles of species traits in vulnerability.