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Figure 8. Swift fox dispersal corridors and habitat connectivity.
Swift fox dispersal corridors
We mapped six different alternative models for swift fox corridors. These consisted of the factorial of relative landscape resistance (high, med, low) and point placement (50, 100). The 100 point placement across the landscape resistances is shown in Figure 8a. Maps of predicted corridors for all six combinations of relative landscape resistance and point placement for Swift fox are available for download (LINK). In this figure, corridor habitat is the area occupied by the colored predicted Guassian kernel density surface.
The figure depicts the pattern of expected corridors and the expected rate of internal movement across each landscape resistance surface. The figure shows the corridors of swift fox across each relative landscape resistance that are concentrated in the southwest with major paths leading to the northwest region.
Swift fox habitat connectivity
We mapped the same nine different alternative models of habitat connectivity, consisting of the factorial of relative landscape resistance (high, med, low) and dispersal ability (10km, 30km, 60km). One of those combinations is shown in Figure 8. In this figure, connected habitat is the area in the left panel occupied by the colored predicted density surface, and in the right panel that is contained in either “core” or “fracture zone” patches. Maps of predicted connected habitat for all nine combinations of connected relative landscape resistance and dispersal ability for Swift fox are available for download (LINK).
Figure 8b depicts the pattern of expected distribution of connected habitat and the expected rate of internal movement across each pixel. The figure shows that connected Swift fox habitat at the Med x 30km combination of relative landscape resistance and dispersal ability is relatively wide spread across the northwestern 2/3 of the study area, with four large core concentrations. The northernmost populations are broken up into two major centers and several smaller isolated subpopulations predicted to be isolated from one another. The large west-central concentration area is largely connected into a single large patch containing several large core areas predicted to have high rates of internal movement linked across fracture zones of attenuated movement. Finally, there are several isolated subpopulations in the southwestern corner of the study area, including one core area predicted to a relatively high density of internal movement based on the records in the Natureserv database used to populate the model.
We calculated the same four FRAGSTATS metrics of landscape composition and configuration on the connected habitat maps for all nine combinations for relative landscape resistance and dispersal ability for swift fox (for a full discussion of metrics, see the final report, phase 1). The metrics are percentage of the landscape occupied by connected habitat (PLAND), number of isolated patches of internally connected habitat (NP), correlation length of connected habitat (CL), and largest patch of connected habitat percentage of the landscape (LPI). At all levels of dispersal ability and relative landscape resistance, there was a very large decrease in the FRAGSTATS metrics between analysis of all connected habitat and only the core connected habitat. Specifically, core habitat comprises about ¼ to 1/2 the total area of connected habitat, and has roughly 1/3 to ½ the connectivity as measured by correlation length and largest patch index. As for the lesser prairie-chicken, the percentage of the landscape, correlation length and largest patch index of connected habitat increase greatly, and the number of patches decreases, with changes in dispersal ability. Also consistent with the lesser prairie chicken, extent and connectivity of connected swift fox habitat is largely independent of the relative values of landscape resistance used in our analysis. For all four landscape metrics dispersal ability had more than 20 times greater effect than variation in relative landscape resistance (relative effects size). Figure 8c displays the combined habitat connectivity and dispersal corridors.
Computational Ecology Laboratory
Division of Biological Sciences (DBS)
The University of Montana
32 Campus Drive, HS 507
Missoula MT, 59812-1002
Phone: (406) 243-2393
Fax: (406) 243-4184