- Metric Name:  Coastal California Gnatcatcher Habitat Suitability

- Data Vintage:  2015

- Unit Of Measure: Habitat Similarity Index (HSI) prediction indicating habitat suitability ranging from zero, the least suitable, to one, the most suitable

- Very High Suitability = HSI values of 0.75 to 1.0

- High Suitability = HSI values of 0.5 to 0.74

- Low to Moderate Suitability = HSI values of 0 to 0.49

This habitat model was developed to delineate a sampling frame for regional monitoring of coastal California gnatcatchers (Polioptila californica californica) to determine: 1) percent area occupied (PAO) in high and very high suitability habitat across conserved lands and participating military lands in the U.S. range in southern California; 2) changes in PAO over time; and 3) extinction and colonization rates. One specific purpose of the model is to identify areas recovering from disturbance, such as wildfire, that may not currently support coastal sage scrub vegetation used by coastal California gnatcatchers but are otherwise highly suitable. This will enable monitoring gnatcatcher occupancy associated with habitat changes over time.

Creation Method: The authors used the “Partitioned Mahalanobis D2” modeling technique to construct alternative models with different combinations of environmental variables. Variables were calculated at each point in the center of a 150 m x 150 m cell in a grid of points across the southern California landscape. Variables reflect various aspects of topography, climate, land use (percent vegetation and urbanization at 150 m and 1 km scales), Normalized Difference Vegetation Index, and modeled California sagebrush (Artemisia californica) habitat suitability. Due to spatial unevenness in gnatcatcher location data, southern California was divided into five sampling regions and randomly subsampled 50 locations from each region. We repeated this process 1,000 times using a total of 1,063 spatially precise and non-redundant gnatcatcher locations as a calibration dataset. For every model-partition, we calculated Habitat Similarity Index (HSI) predictions for presence and pseudo absence points ranging from Very High (0.75 - 1.00); High (0.50 - 0.74); Low (0.25 - 0.49); and Very Low (0 - 0.24). Suitable habitat is identified as grid cells with HSI greater than or equal to 0.5. We calculated Area Under the Curve (AUC) values from a Receiver Operating Curve (ROC) to determine how well models distinguish between presence and pseudo-absence points. We selected a best performing calibration model and partition based upon median HSI calibration and validation values and AUC results. This model includes the following variables: average minimum January and maximum July temperatures, annual precipitation, elevation, northness, eastness, slope, topographic heterogeneity (30 m x 30 m neighborhood), percent of urban, coastal sage scrub and chaparral land cover at 150 m scale, and predicted California sagebrush habitat suitability. We mapped HSI predictions for each cell in the 150 m-scale grid across the study area.

Source: USGS; Kristine Preston; Coastal California Gnatcatcher Habitat Suitability Model for Southern California (2015) - ScienceBase-Catalog

- Credits:  USGS

US Geological Survey Geosciences and Environmental Change Science Center: 
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