Twist number statistics as an additional measure of habitat perimeter irregularity

Individual habitats are altered by the surrounding landscape matrix. Quanti tative analysis of habitat boundary is therefore necessary. A shape index i s proposed based on the perimeter twist number; twists divide the patch per imeter in seperate segments. Using Principal Components Analysis, the shape index is compared with fractal dimension (per-patch calculation based on a rea and perimeter) and with four shape (compactness) indices based upon pix el geometry, next to area and perimeter statistics. The analysis is execute d with simulated data based on percolation maps. The proposed index can be used as a complementary shape descriptor because of (i) its independence of fractal dimension, (ii) its restricted correlation with only one compactne ss index and (iii) its ability to identify habitats characterized by limes divergens and a high interior-edge ratio.