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<br />in 1995 (Stevens et ai" 1995), Vaseys Paradise is a popular water source and attraction site for
<br />Colorado River rafters; however access is limited by the dense cover of poison ivy
<br />(Toxicodendron l:YdberiiO and the nearly vertical terrain (Stevens, et ai" 1995), Within Grand
<br />Canyon, KAS is apparently restricted to Vaseys Paradise: no KAS were observed at 81 other
<br />Grand Canyon springs surveyed from 1991 to 1995, Rematched historic photographs ofVaseys
<br />Paradise (e,g, Turner and Karpiscak 1980:58-59) reveal that vegetative cover has increased
<br />greatly at lower stage elevations since completion of Glen Canyon Dam,
<br />
<br />Stevens, et ai, defined primary habitat at Vaseys Paradise as crimson monkey-flower (Mimulus
<br />cardinali~) and non-native water-cress (Nasturtium officinalll); and secondary, or marginal, habitat
<br />is defined as patches of other riparian vegetation that are not dominated by monkey-flower or
<br />water-cress, and not used by KAS, Land surveys in 1995 revealed rapid changes in vegetation
<br />cover over the growing season, with 5,9"10 to 9.3% of the primary habitat occurring below the
<br />33,000 cfs stage, and 11.1% to 16,1% occurring below the 45,000 cfs stage, The total area of
<br />primary habitat was 0,22 acres, secondary habitat area was 0,22 acres, and the total vegetated
<br />area of the spring was 0,44 acres in June, 1995,
<br />
<br />The total estimated Vaseys Paradise KAS population rose from 18,476 snails in March up to as
<br />many as 104,000 snails in September, 1995 as reproduction took place in mid-summer (Stevens et
<br />ai" 1995), The proportion of the total estimated KAS population occurring below the 33,000 cfs
<br />stage rose from 1,0% in March to 7,3% in September, and that occurring below the 45,000 cfs
<br />stage was 3,3% in March, 11.4% in June and 16.4% in September, 1995,
<br />
<br />Life Requisites
<br />
<br />KAS occurs on cattail (IIilha sp,) at Three Lakes, near Kanab, Utah, and cattail is the dominant
<br />macrophyte at that locality, In contrast, Vaseys Paradise is a fast-flowing, coo~ dolomitic-type
<br />spring, with abundant wetland and phreatophyte vegetation, including native crimson monkey-
<br />flower, poison ivy and non-native water-cress. Crimson monkey-flower and non-native water-
<br />cress are perennial aquatic wetland or hydrophytes (Kearney and Peebles 1960), and KAS was
<br />almost completely restricted to those two species along the edges of the Vaseys Paradise stream
<br />(Stevens et ai" 1995), KAS was rare to absent on other plant species and substrata in 1995,
<br />Introduction ofwater-cresa provided KAS with an alternate host plant, and completion of Glen
<br />Canyon Dam increased overall primary habitat area at Vaseys Paradise by approximately 40%,
<br />
<br />Demographic ana1yses based on size class distribution indicated that KAS is essentially an annual
<br />species, with much of the population maturing and reproducing in mid-summer (July and August),
<br />and most snails over-wintering as sma1l size classes (Stevens et a1., '1995). Loose, gelatinous egg
<br />masses were observed on the undersides of moist to wet live stems, on the roots of water -cress,
<br />and on dead or decadent stems of crimson monkey-flower in August, 1995, No data on egg
<br />. development or emergence success are avai1able,
<br />
<br />KAS at Vaseys Paradise were parasitized by a trematode, tentatively identified as
<br />
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