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The 1987 sites varied in both size and shape. Those that were inaccessible by road, could be visited only once. Temporal replication was necessary because of phenological differences among butterflies; for example, some species emerge early in the summer. whereas others emerge in late summer. To increase the number of temporal replicates, I sampled only 24 sites in 1988 and 1989; this was the maximum number that could be visited at least twice during the summer. Thus, each site was surveyed more intensively, but the Park, as a whole, was sampled less extensively. Nonetheless, the 24 sites selected are representative of the range of geographic and environmental variation within the Park (Fig. 1). Each of the 1988-89 sampling sites was 1 square kilometer as defined by Universal Transverse Mercator coordinates on USGS topographic maps. Field experience in 1987 indicated that sampling sites must be at least this size to represent the range of small-scale patchiness and microhabitats adequately.

Fig. 1. Glacier National Park biodiversity sites for butterflies in 1988 and 1989. Open circles represent sites surveyed during only one year, whereas closed circles represent sites surveyed during both 1988 and 1989. See Debinski (1991) for detailed descriptions and names of sites.

Although standard community-sampling procedures call for use of sampling sites that are homogeneous in structure and composition (Gauch, 1982), I chose to maximize sampling of habitat diversity in the 1988-89. Nonetheless, the 24 sites selected are representative of the range of geographic and environmental variation within the Park (Fig. 1). Each of the 1988-89 sampling sites was 1 square kilometer as defined by Universal Transverse Mercator coordinates on USGS topographic maps. Field experience in 1987 indicated that sampling sites must be at least this size to represent the range of small-scale patchiness and microhabitats adequately. Although standard community-sampling procedures call for use of sampling sites that are homogeneous in structure and composition (Gauch, 1982), I chose to maximize sampling of habitat diversity in the 1988-89 sites for two reasons. First, this study was designed to inventory species occurrences across a very large area; thus, site homogeneity was ignored to maximize broadscale coverage. Second, because I observed in 1987 that species diversity was much higher along ecotones, I included ecotones in many of the sites. Nevertheless, broad habitat-type characterizations were still possible at each site.

This particular design resulted in a certain bias. Vegetational types or ecological space defined by position on the topographic-elevational gradient were not sampled in direct proportion to their frequency of occurrence in Glacier National Park. Instead, some of the rarer habitats were overrepresented as I attempted to sample rare species and to increase coverage of ecological space along temperature and moisture gradients. The primary disadvantage of this approach is in statistical analysis of the data; the perceived rarity of a species may not be indicative of its true rarity in Glacier National Park.