Polygonal representation of least-cost corridors (primary model) - A landscape connectivity analysis for the coastal marten (Martes caurina humboldtensis)

This dataset is a polygonal representation of the least-cost corridors produced by our habitat connectivity model for the coastal marten.  This polygonal representation was derived from the full raster output of least-cost corridors in our model, using a cutoff of 4885 cost-weighted meters.  The development of the least-cost corridors and the rationale for selecting a cutoff value of 4885 cost-weighted meters is described below in greater detail:

After developing the coastal marten landscape resistance surface (i.e. movement model) and mapping habitat cores, we used Linkage Mapper to identify Least-Cost Paths (LCPs) between cores and to map broader mosaicked corridors around these single-pixel width paths.  Linkage Mapper proceeds through several steps to complete these tasks (McRae and Kavanagh 2016).  First, it identifies and lists which habitat cores are nearest neighbors using both the Euclidean distance (the “as-the-crow-flies” straight-line distance between nearest points on the edges of a pair of cores regardless of the character of the intervening landscape) and the cost-weighted distance (CWD).  Second, it creates a “stick map” using straight-line linkages to connect core area pairs that are candidates for corridor mapping.  Third, it locates the LCPs through the resistance surface between these pairs of cores and calculates their cost-weighted distance.  This LCP is a single 30m pixel wide.  A single pixel’s cost-weighted distance is the cell’s resistance value multiplied by the size of the cell, and the cost-weighted distance of an LCP is the sum of the cost-weighted distances of the pixels it runs through.

This allows CWD to be reported in units that are directly comparable to the LCP length and the Euclidean distance between habitat cores (i.e. normalized to meters or kilometers), and all three of these metrics are included in the Linkage Mapper output for each linked pair of cores.  Finally, Linkage Mapper creates least-cost corridors, which are wider swathes surrounding the LCPs that have only slightly higher movement costs and are more biologically realistic for conservation planning.  It does this by calculating for each pixel on the landscape how much more costly a pathway passing through it between two cores would be than the LCP.  Pixels closest to the LCP tend to be relatively close to it in CWD value, with the potential contribution of pixels to connectivity tending to decrease further away from the LCP.  Linkage Mapper then creates a composite linkage map by assigning each pixel its minimum value relative to the nearest LCP (WHCWG 2010).  Thus, the final map is a mosaic of normalized least-cost corridors around the LCPs.  These corridors will vary in width depending on the resistance values surrounding the LCP.  The creation of mosaicked corridors is the most fundamentally important function of Linkage Mapper in providing an informative depiction of habitat connectivity on the landscape, and is a significant advance over the simple LCP estimation that is a basic function available in ArcMap.  

The output of this least-cost corridor mosaic is a continuous surface that can be interpreted in various ways depending on how the relative values of pixels on the landscape are rendered in the final mapping process (WHCWG 2010).    After some experimentation, we chose to depict corridors using a color ramp scaled from 0 – 4885 cost-weighted meters (i.e. the sum of the resistance values of the cells multiplied by their size to normalize them for comparison to meters).  The specific value of the upper end of this scale was based on five times the radius of an average female coastal marten home range (977m X 5 = 4885m).

This is an abbreviated and incomplete description of the dataset.  Please refer to the spatial metadata for a more thorough description of the methods used to produce this dataset, and a discussion of any assumptions or caveats that should be taken into consideration.

Tags: coastal-marten, connectivity-modeling, general-biology-at-risk-biota-te-species, general-biology-species-mammals, general-landscapes-landscape-dynamics, general-landscapes-landscape-ecology, general-management-habitat-management-habitat-models, general-management-landscape-management-landscape-connectivity, gnarly-landscape-utilities, humboldt-coastal-marten, humboldt-marten, least-cost-path-analysis, linkage-mapper, martes-caurina-humboldtensis, pacific-marten
Organization: Department of the Interior