. Bulletins of American paleontology. MoLLUSKS Past and Present: Brewster-Wingard et al. 203. 20 25 Salinity (ppt) Text-figure 2.—Plot of temperature {°C) versus salinity (ppt) recorded at sites from February 1996 through July 1999. Histogram on x axis shows frequency of observations in 5 ppt increments. Histogram on y axis shows frequency of observations in 5°C increments. Bimodal nature of temperature readings reflects seasonality. Constancy = (Occurrence-100) ^ Total number of samples in cluster. A species with 100% constancy is present in every sample in a given cluster. Fidelity is a meas
. Bulletins of American paleontology. MoLLUSKS Past and Present: Brewster-Wingard et al. 203. 20 25 Salinity (ppt) Text-figure 2.—Plot of temperature {°C) versus salinity (ppt) recorded at sites from February 1996 through July 1999. Histogram on x axis shows frequency of observations in 5 ppt increments. Histogram on y axis shows frequency of observations in 5°C increments. Bimodal nature of temperature readings reflects seasonality. Constancy = (Occurrence-100) ^ Total number of samples in cluster. A species with 100% constancy is present in every sample in a given cluster. Fidelity is a measure of how unique a species is to a given cluster (expressed as a percentage). The formula is Fidelity = [(Constancy in Cluster X) -^ (S constancy values for all clusters)]-100. Thus, it is possible for a species to have a high con- stancy value, if it is present in most samples in a clus- ter, but a low fidelity value if it also is commonly present in other clusters. Conversely, a species can be very rare and have a low constancy for a cluster, but a high fidelity because it occurs only in that cluster. A species with 100% fidelity is unique to that cluster. Several measures of diversity were calculated on all piston core samples: 1) total number of individual mol- luscan specimens; 2) faunal richness; 3) evenness; and 4) Shannon's diversity index. Faunal richness in this study is a measure of the number of faunal groups present in a given sample (in the case of the presence- absence data observed at a given site). In some cases, the fauna are grouped into genera and occasionally broader categories ( marginellids), so this is not '"species" richness in the usual sense. Evenness and Shannon's diversity index were calculated using MVSP. Evenness is a measure of how evenly dispersed the total number of individuals are among the faunal categories; the higher the value, the more evenly dis- persed the individuals are. Shannon's diversity index (Shannon and Weaver
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