Herpetofauna in Riparian Habitats Along the Colorado River in Grand Canyon 1

This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. Herpetofauna in Riparian Habitats Along the Colorado River in Grand Canyon 1 2 Peter L. Warren and Cecil R. Schwalbe Abstract.--Lizard population densities and species composition were sampled in riparian and non-riparian habitats along the Colorado River. The highest densities were found in shoreline habitats, moderate densities in riparian habitats and lowest densities in non-riparian habitats. Rapidly fluctuating river flow levels may have a deleterious effect on lizard populations by trapping populations on alluvial bars and inundating nest sites. For years riparian habitats have been recognized as making a contribution to the densities in upland vegetation may actually be structural diversity and species richness of higher. natural communities that exceeds the relative areal extent of those habitats. The availability One group that has received relatively little of additional water permits growth of plant attention with respect to the importance of species and growth forms that are lacking in the riparian habitats to their density and diversity surrounding upland vegetation. Their occurrence is the reptiles. It is common to find comments in in turn provides food and habitat resources the literature about the higher density of some without which some animal populations may not species in riparian sites (Lowe and Johnson, 1977; otherwise persist in the upland community. To Vitt and Ohmart, 1977; Tinkle, 1982) and some most biologists these patterns are obvious, but in studies of lizard demography have been performed many cases they are surprisingly poorly in riparian areas (Tinkle, 1976; Tinkle and documented. Dunham, 1983; Vitt and Van Lohen Sels, 1976). However, quantitative studies comparing reptile Some of the best studied examples of the density and diversity in riparian and adjacent contribution of riparian habitat to local species non-riparian habitats are few. Only recently has density and diversity are for birds and mammals. emphasis on riparian ecosystems has begun to Gallery forests of cottonwood and willow along address effects of management practices and exotic some Southwestern rivers have been shown to have riparian vegetation on riparian reptile some of the highest densities of nesting birds in communities (Szaro et al., 1985; Jakle and Getz, North America, much higher than in surrounding 1985; Jones and Glinski, 1985). semiarid upland sites (Johnson et al., 1977; Anderson, Higgins and Ohmart, 1977). Riparian The present study was designed to examine the habitats contribute breeding sites, feeding areas patterns of distribution of reptile species and migratory routes for birds. Hammal species relative to riparian habitats along the Colorado diversity is also higher along watercourses, where River in Grand Canyon National Park. This work is some species find necessary cover that is lacking part of a larger study to determine the effects of in more open adjacent arid vegetation (Anderson, fluctuating flows from Glen Canyon Dam on plant Drake and Ohmart, 1977), although small mammal and animal populations in and along the Colorado River. Data presented here were gathered during constant flow levels of approximately 40,000 cubic 1 feet per second (cfs) in June and 25,000 cfs in Paper presented at the First North American August, 1984. Additional censuses will he made Riparian Conference [University of Arizona, during lower, fluctuating flow levels. The Tucson, April 16-18, 1985]. results presented here are from the first year of 2 a multi-year project, and are restricted to only Peter L. Warren is Research Assistant at the those species for which the most data were Arizona Remote Sensing Center, Office of Arid gathered, the diurnal lizards. Lands Studies, University of Arizona, Tucson, Arizona. Cecil R. Schwalbe is Herpetologist with Nongame Branch, Arizona Game and Fish Department, 2222 W. Greenway Road, Phoenix, Arizona. 347 STUDY AREA Habitats Sampled We censused lizard populations at a series of Sampling was performed in ten different sites along the Colorado River above and in Grand habitats that are distributed in three zones Canyon National Park beginning near Lees Ferry and relative to the river. The first zone comprised extending downstream 220 miles almost to Diamond shoreline habitats within 5 meters of the river Creek. The elevation at river level is shore. The second zone included all riverine approximately 945 meters (3,100 feet) at Lees riparian vegetation greater than five meters from Ferry and drops to 427 meters (1,400 feet) at the the river shore. The third zone included non last census locality at mile 220. The vegetation river habitats, both upland and riparian (Table through which the river flows is generally Mohave 1). desertscrub. However, there is a gradual transition in species composition from more cold Three distinct habitats were sampled in the tolerant species at the upper end of the study river shoreline zone. These were cobble shore, area to a flora composed of many frost-sensitive rocky shore, and cliff faces at the water's edge. species at the lower end (Warren et al., 1982). In all cases shoreline samples were characterized by low vegetation cover, usually less than ten The riparian corridor along the river is percent. Cobble shores generally were charac characterized by two vegetation zones that are terized by num~rous rocks less than 0.5 meters in more or less distinct in species composition and diameter and rounded by erosion. Larger, uneroded distribution. Previous to the construction of boulders were absent and large patches of bare Glen Canyon Dam in 1963 the river channel was sand were occasional. Cobble shores generally were scoured by floods on a regular basis, and the only found at the mou~hs of tributary canyons where the riparian vegetation occurred as a belt along the coarse alluvium that forms level cobble bars was high water line where flood disturbance was at a washed into the river. m1n1mum. Since dam construction lack of large volume flooding has permitted plants, many of them exotics, to grow along the water's edge (Turner and Karpiscak, 1980). The resulting pattern is Table 1.--Location of study sites at which lizard one in which the original riparian vegetation, transect sampling was performed. The number consisting largely of mesquite (Prosopis of habitats sampled in each vegetation zone glandulosa) and cat-claw acacia (Acacia greggii), is indicated for each site. is perched on talus slopes and alluvial terraces several meters above the current normal water Site River Shore River Non level. The new riparian vegetation, dominated by Name Mile line Riparian River tamarisk (Tamarix chinensis) and arrowweed Lee's Ferry -1R 1 1 (Tessaria sericea), occupies sand and cobble bars along the water's edge. Badger 8R 1 none 16L 1 none 20R 1 North Canyon 20.5R 1 METHODS none 43.5L 1 Saddle Canyon 47R 1 3 1 Visual belt transects, modified from the Nankoweep 53R 2 3 2 Emlen (1971) bird census technique, were used to Kwagunt 56R 1 census the common diurnal species (Lowe and Cardenas 71L 1 4 Johnson, 1977). This method involves walking a Cremation 86L 1 transect through representative areas of the none 94L 1 target habitats and recording all individuals Crystal 98R 1 observed within a belt of predetermined width of Bass 108.5R 1 2 1 four meters. Transect length varies with size of Elves Chasm 116.5L 1 1 the habitat patch, but usually varied from 100 to Forster 123L 2 300 meters in length. Transect sites were Tapeats 134R 1 1 selected to sample a range of variation within none 140L 1 1 old- and new-riparian habitats and in adjacent Kanab 143.5R 1 4 non-riparian desertscrub. The time of day at the National 166L 2 1 beginning and end of each transect was recorded as 171R 1 well as a temperature profile consisting of soil Stairway 2 none surface temperature, air temperature at 5 mm and 185R 1 3 1 air temperature at 1.5 m. Weather conditions such Whitmore 188R 3 Parashant as cloudiness and wind speed were also noted. 198R 1 3 1 Granite Park 209L 1 1 Three Springs As each individual lizard was sighted, the 216L 1 220 mi. Canyon 220R 1 distance along the transect and the substrate upon which it was first observed were recorded, as well Total Transects 24 36 8 as its sex and age, when possible. The substrate categories used were bare soil, litter, rock (less Total Transect than one meter diameter), boulder (greater than Length (meters) 2665 5522 2420 one meter diameter), cliff face, or tree. When individuals were in a tree, the tree species and height above ground were also recorded. 348 In contrast, rocky shores were composed of can be considered "new-zone" or post-dam habitats. rock fragments of varying sizes ranging from These were open tamarisk with 15 to 40 percent cobbles up to boulders several meters in diameter. cover, dense tamarisk with 60 to 100 percent These shores were generally composed of uneroded cover, and arrowweed with cover similar to the talus and rockfall debris and may include pockets open tamarisk. of bare sand of varying sizes that were trapped among the boulders. In contrast to the level Finally, two habitats were sampled in the cobble shores, rocky shores usually fell steeply non-river zone. These were desertscrub on canyon to the water's edge and were commonly very rugged slopes generally ranging from 15 to 30 percent and irregular. slope with 15 to 30 percent vegetation cover, and non-river riparian habitats along perennial Sandy shores and heavily vegetated shores tributary streams. were examined but not sampled systematically for several reasons. Heavy vegetation immediately at RESULTS AND DISCUSSION the water's edge was relatively uncommon.

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