Methods
Data
Two main GIS layers were developed incorporating ecosystem and urbanisation datasets. For the ecosystem layer, the National Land Cover Dataset 2001 (NLCD) with 30 m cell size was obtained from the United States Geological Survey (USGS). Among 14 land cover classes originally available for the study area, only four natural land types were selected as critical ecosystems represented in Maricopa County. These included desert shrub, grassland, agricultural land, and maintained open space. While desert shrub and grassland are undoubtedly ecosystem types being typically protected, conserving agricultural land is often a controversial subject contingent upon normative values. Nevertheless, this study takes the agriculturallands as one of the essential ecosystem types into account, due to their biological, environmental, and cultural importance in the regional context. Maintained open space was included since recent literature stresses that even small-scale green patches can be a habitat for urban species that need to adapt to an urban environment (McKinney, 2002; Small et al., 2006) or at least serve as ecological stepping-stones in the landscape mosaic (Angold et al., 2006). To increase the data accuracy in the classification, the NLCD data were compared with local land use data. The maintained open spaces were confined to urban land uses such as neighbourhood parks, golf courses, street trees, residential gardens, and temporary green fields in vacant lots. The desert shrubs appeared in a variety of land uses ranging from large outlying desert patches (which are mostly used for passive open spaces) to vacant areas, urban parks, and small, fragmented spaces in built-up areas. A small area of the Tonto National Park falls within the study area; however, forest-related classes were excluded from the ecosystem layer due to the marginalised location, which make forest ecosystems beyond the scope of this research that focuses interactions at the urban–wildlife interface.