Comparing habitat suitability and connectivity modeling methods for conserving pronghorn migrations

Abstract

Terrestrial long-distance migrations are declining globally: in North America, nearly 75% have been lost. Yet there has been limited research comparing habitat suitability and connectivity models to identify migration corridors across increasingly fragmented landscapes. Here we use pronghorn (Antilocapra americana) migrations in prairie habitat to compare two types of models that identify habitat suitability: maximum entropy (Maxent) and expert-based (Analytic Hierarchy Process). We used distance to wells, distance to water, NDVI, land cover, distance to roads, terrain shape and fence presence to parameterize the models. We then used the output of these models as cost surfaces to compare two common connectivity models, least-cost modeling (LCM) and circuit theory. Using pronghorn movement data from spring and fall migrations, we identified potential migration corridors by combining each habitat suitability model with each connectivity model. The best performing model combination was Maxent with LCM corridors across both seasons. Maxent out-performed expert-based habitat suitability models for both spring and fall migrations. However, expert-based corridors can perform relatively well and are a cost-effective alternative if species location data are unavailable. Corridors created using LCM out-performed circuit theory, as measured by the number of pronghorn GPS locations present within the corridors. We suggest the use of a tiered approach using different corridor widths for prioritizing conservation and mitigation actions, such as fence removal or conservation easements.

Figure 1. Study area and migration locations.

Location of the study area in Montana and Saskatchewan (A) and pronghorn migrations for the spring of 2008 and 2009 (circles) and the fall of 2008 and 2009 (crosses) and the habitat patches (outlined in black) (B).

Figure 2. Corridors created using 10% threshold.

Least-cost modeling (solid line) and Circuitscape (shaded area) pronghorn migration corridors in Montana and Saskatchewan created from the 10% most traversable habitat on Maxent and Analytic Hierarchy Process resistance surfaces for fall (A) and (B), respectively, and spring (C) and (D) migration seasons.

Figure 3. Pronghorn and area included within spring corridors.

Percent of pronghorn locations and study area in Montana and Saskatchewan for the spring pronghorn connectivity models. Maxent resistance surface and least-cost modeling (LCM) (A), Analytic Hierarchy Process (AHP) resistance surface and LCM corridors (B), Maxent resistance surface and Circuitscape (C) and AHP resistance surface and the Circuitscape connectivity model (D).

Figure 4. Pronghorn and area included within fall corridors.

Percent of pronghorn locations and percent of study area within Montana and Saskatchewan for the fall pronghorn connectivity models. Maxent resistance surface and least-cost modeling (LCM) (A), Analytic Hierarchy Process (AHP) resistance surface and LCM corridors (B), Maxent resistance surface and Circuitscape (C) and AHP resistance surface and the Circuitscape connectivity model (D).

Figure 5. Top corridors and suggested Pronghorn Priority Areas.

The top corridors identified (the least-cost model-Maxent 1%–15% corridors) for fall (blue) and spring (yellow)(A) and the resulting recommended tiered Pronghorn Priority Areas, created from the 1% corridors (Tier 1, dark green), 5% corridors (Tier 2, medium green) and 10% LCM-Maxent corridors (Tier 3, light green) (B).