Integrating structural and functional connectivity to optimize ecological security patterns at multiple levels in the Yellow River Delta, China

Improving ecological connectivity is essential for optimizing ecological security patterns (ESPs) to conserve biodiversity and support regional sustainability. However, the synergistic quantitative evaluation and optimization of ESP connectivity integrating structural and functional dimensions remain poorly understood. Here, we developed an integrated framework coupling structural and functional connectivity to optimize ESPs at multiple hierarchical levels in the Yellow River Delta (YRD). The results showed that the numbers of ecological sources in the YRD declined from 91 in 1990 to 23 in 2020, while ecological corridors decreased from 181 to 31, with a spatial shift from inland to coastal areas. The α, β, and γ declined by 57.30%, 32.24%, and 27.41%, respectively, and the connectivity robustness was also weakened over time. In 2020, 19 ecological pinch points (1.06 km2) and 10 barrier points (0.41 km2) were identified as restoration priorities. Three restoration scenarios exhibited contrasting outcomes. Structural optimization increased the selected topological connectivity metrics but did not reduce modeled movement resistance, whereas functional optimization reduced corridor length and cost-weighted distance (CWD) but resulted in lower values of some structural metrics. The coupled scenario increased the selected structural metrics while reducing corridor length, suggesting the potential for coordinated improvements in network structure and landscape permeability under the model assumptions. A spatial strategy of "three cores, two zones, two belts, and multiple points" was proposed to guide targeted protection and restoration. This study highlights the necessity of multi-perspective ESP optimization and provides guidance for coastal ecological restoration and sustainable management.