Modeling Habitat Connectivity for the Monarch Butterfly among Protected Areas and its Significance in Conservation
Criteria for resistance map
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Streams cost = 0
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Monarchs do not eat over their wintering period but require close proximity to streams to drink during their diapause. Since they are able to fly, crossing streams is not a problem.
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Water bodies cost = 10
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Water bodies are slightly more difficult to cross because they are larger however still minimal cost because they are able to fly.
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Roads cost = 1,000
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There is a large cost to roads because a butterfly flying low or just basking on the ground near roads will perish.
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Elevation cost (under 2890 m)= 400
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A study by Bojórquez-Tapia (2003) found that preferred habitats of overwintering monarchs were of high elevations (altitudes over 2890 m) so anything under this level will be high cost.
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Protected areas = 0
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These areas provide habitat for the monarch’s and therefore have no cost associated with them.
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Note: when changing my protected areas into raster format, because the cell sizes had to be the same for each criteria, many small patches were lost in the transformation because patches were too small. This could have implications in my connectivity analysis if small patches (that could act as stepping stones) are lost.
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Linkage Mapper
Linkage Mapper is a program that uses GIS maps of core habitat areas and resistance maps to identify map linkages between core areas. Before a resistance map could be created, first all the polyline and polygon features (Figure 3) needed to be converted into raster format (Figure 4). Each cell in my resistance map is attributed with a value reflecting the risk or difficulty of moving across that cell. The higher the value, the more difficult it is to cross that path. The criteria of reclassifying each layer into a resistance map (Figure 5) is as follows:
Figure 4: Raster data
All polygons and polyline data were converted to raster using feature polygon to raster tool or polyline to raster tool. Coloured Protected areas=0, roads=1000, streams=0, water bodies=10, **elevation=400 below 2890 (not shown in map)
Figure 3: Criteria for resistance map
This map is a collection of polygon and line data from various sources (see sources in methods section above). This includes protected areas, roads, streams, water bodies, and elevation (not shown).
Figure 5: Resistance map
This figure was created by combining all raster data into one raster using mosaic raster tool in order to create a resistance map as an input into linkage mapper.
Figure 6: Euclidean distances between patches
Euclidean (straight-line) distances were computed using Conefor Sensinode 2.2 and represent the distances between polygon edges on the map.
Figure 7: Least-cost paths between patches
Linkage Mapper uses core area polygons, resistance raster and a link table computed to perform cost-weighted distance calculations from each core area. Least-cost path lines are attributed with various linkage statistics (e.g the total cost-weighted distance traversed by the linkage). From the data we can see that smaller patches that are farther away are less connected, and larger patches that are closer to one another maintain connectivity.