1. Introduction
1.1 Background
The Linkage Pathways Tool of the Linkage Mapper Toolbox is a GIS tool designed to support
regional wildlife habitat connectivity analyses. It consists of several Python scripts, packaged as
an ArcGIS tool, that automate the mapping of wildlife habitat corridors.
Linkage Pathways uses vector maps of core habitat areas and raster maps of resistance to
movement to identify and map least-cost linkages between core areas. Each cell in a resistance
map is attributed with a value reflecting the energetic cost, difficulty, or mortality risk of moving
across that cell. Resistance values are typically determined by cell characteristics, such as land
cover or housing density, combined with species-specific landscape resistance models. As
animals move away from specific core areas, cost-weighted distance analyses produce maps of
total movement resistance accumulated.
The scripts use ArcGIS and Python functions to identify adjacent (neighboring) core areas and
create maps of least-cost corridors between them. The scripts then normalize and mosaic the
individual corridor maps to create a single composite corridor map. The result shows the relative
value of each grid cell in providing connectivity between core areas, allowing users to identify
which routes encounter more or fewer features that facilitate or impede movement between core
areas.
We developed these scripts to support the 2010 Washington Wildlife Habitat Connectivity
Working Group (WHCWG) statewide connectivity analysis, and public them public for use in
other wildlife connectivity assessments. More details on the models and algorithms implemented
by Linkage Pathways can be found in Chapter 2 and Appendix D of WHCWG (2010).
Enhanced Modules–The toolbox now includes newly developed tools to map pinch-points
within corridors (using Circuitscape) , map core areas and corridors with high network centrality
(i.e. those that are most important for keeping a network connected), map barriers (some of
which may offer restoration opportunities), the relative priority among all the linkages on a
landscape, and map corridors that follow climatic gradients to facilitate species range shifts in
response to climate change. Please see the Pinchpoint Mapper, Centrality Mapper, Barrier
Mapper, Linkage Priority, and Climate Linkage Mapper user guides included with the
Linkage Mapper download.
1.2 Before you begin– a note about connectivity modeling and software
limitations
Linkage Pathways was developed to automate some of the arduous and time-consuming steps of
connectivity modeling. However, even with tools like this one, connectivity modeling involves a
great deal of research, data compilation, GIS analyses, and careful interpretation of results.
Defining core areas, parameterizing resistance models, and other modeling decisions you will
need to make are not trivial. Before diving in, we strongly recommend that users thoroughly
familiarize themselves with the process and challenges of connectivity modeling by consulting
published resources. Good places to start include an overview of habitat and corridor modeling
on the Corridor Designer website (http://corridordesign.org/designing_corridors), WHCWG
(2010), Beier et al. (2011), and references listed within. See Sawyer et al. (2011) for a critique of
current corridor modeling practices.