Determining the suitable distance thresholds for the analysis and optimization of landscape functional connectivity

With the increasing fragmentation of global natural habitats,it is of great significance to analyze the effects of species dispersal distance on landscape connectivityand further determinate the suitable distance thresholds in order to discover vulnerable landscape links and identify important habitat patches. Current studies pay more attention to landscape functional connectivity, yet the selection of distance thresholds is often random. Taking the grassland of Poyang Lake as research object, this study firstly determined the spatial distribution of grassland at each water level. Then, the functional connectivity and the importance of patches for grassland were simulated under different dispersal distance scenarios to determine the suitable distance thresholds with the help of the graph-theoretic connectivity indices and habitat patch importance evaluation. Our results indicated as follows: (1) Grassland was submerged and divided by water, and its shrinkage coexisted with fragmentation when the water level rose. While the grassland emerged and spliced, and its expansion co-occurred with cohesion when the water level fell. (2) Landscape functional connectivity showed positive relationship with species dispersal distance. Grassland functional connectivityincreasedprogressively with increasing dispersal distance. 600m-1000 m can be selected as the suitable distance range for the analysis of grassland connectivity pattern.In this range, grassland functional connectivity varied little, which helps to find small components and isolated patches with weak risk resistance and discover vulnerable landscape links in time. (3) Species dispersal distance also had significant influence on the importance of habitat patches. The important patches showed spatial differentiation and the importance of large patches was remarkable while the importance of small patches was masked with increasing dispersal distance. 800 m was finally determined as the optimal distance threshold for the optimization of grassland connectivity pattern. At this distance, the distribution pattern of important patches was stable and the importance of both large and small patches can be highlighted, which is conducive to effectively identifying the important patches that play an extremely vital role in maintaining landscape connectivity. This finding can propose scientific reference for improving landscape connectivity and identifying conservation priorities of habitat patches.