American pikas inhabit low-elevation sites outside the species’ previously described bioclimatic envelope

It has been suggested that Nearctic pikas ( Ochotona spp.) are good biogeographic indicators of regions containing rocky, mesic, and cool habitat characterized by long winters and short summers. I examined whether populations of pikas inhabiting distinct low-elevation locales (121–255 m) are faithfully restricted to long-winter and shortsummer conditions by monitoring the climate associated with American pikas ( Ochotona princeps ) in the southern part of the Columbia River Gorge, Oregon. Ambient air temperatures and weather conditions in the vicinity of 4 pika-occupied rockslides were monitored with remote temperature loggers and weather stations from June 2000 to June 2001. Temperatures were compared to long-term averages recorded within the area. I detected pikas inhabiting locales where some temperatures lie outside of the limiting climatic values previously calculated for regions containing pikas. Mild winter temperatures at these pika locations show that long-winter temperatures and snow accumulation associated with typical habitat may not be requirements for pikas in some low-elevation habitat. When using climatic conditions experienced by extant pikas to estimate local paleoenvironments surrounding fossil sites and to anticipate effects of climate change on future pika distributions, I determined that pika sites in the Columbia River Gorge indicate that the association of pikas with long-winter habitat should be considered uncertain. These results highlight the need for further investigation into how local temperatures affect the distribution, behavior, and persistence of low-elevation pikas.     

Observations on the reproduction, sources of mortality, and diet of the Kendall Warm Spring dace

The life history of the endangered Kendall Warm Springs dace ( Rhinichthys osculus thermalis ) is largely unknown. Our study of its reproduction, sources of mortality, and diet indicated that Kendall Warm Springs dace seem to be reproductively active throughout the year, but the rate of reproduction appears to decrease during the winter. Males become sexually mature at 34 mm total length and females at 40 mm total length. We observed 2 sources of mortality: (1) emigration from the warm spring over a waterfall into the Green River and (2) predation on larvae by dragonfly ( Libellula saturata ) nymphs. Stomachs of Kendall Warm Springs dace contained small (≤ 1.5 mm total length) benthic invertebrates, primarily dipterans and mollusks.     

Comparative tolerance of four stocks of cuttthroat trout to extremes in temperature, salinity, and hypoxia

Four stocks of cutthroat trout ( Oncorhynchus clarki ) were exposed to high temperature, high salinity, and low dissolved oxygen to determine inherent differences. The fish tested included 2 stocks of Bonneville cutthroat trout ( O. c. utah ), a lacustrine stock derived from Bear Lake and a fluvial-origin stock from southern Utah (Manning Meadow Reservoir). The other 2 stocks tested were from Electric Lake (largely Yellowstone cutthroat trout, O. c. bouvieri ) and Jackson Hole, Wyoming (fine-spotted Snake River cutthroat trout, O. c. subsp.). Temperature tests were either critical thermal maximum (CTM) or 96-hour trials using juveniles acclimated between 12.5° C and 18.0° C. Two CTM end points were temperature at first loss of equilibrium (CTM eq ) and onset of spasms (CTM s ). There were no significant differences in CTM eq among test fish acclimated to 18.0° C, but CTM s was significantly higher for Bear Lake Bonneville (30.0°C) than for Snake River (29.6° C) or southern Bonneville (29.7° C) stocks. With fish acclimated at 13.0° C, there were no significant differences among the stocks in CTM eq or CTM s . Differences among stocks varied significantly among nine 96-hour tests. Overall, it appeared that the southern Bonneville stock had slightly better survival at warmer temperatures than other stocks. In 24-hour survival tests at high salinities, the Snake River stock had the lowest tolerance, with significant mortality occuring at 18% (29.5 mS · cm -1 conductivity). The southern Bonneville stock had the highest tolerance, with no mortality until 22% (38 mS · cm -1 ). Bear Lake Bonneville and Electric Lake stocks had 60% and 30% mortality, respectively, at 21% (36 mS · cm -1 ). Hypoxia tolerance measured by resistance time, 24-hour mortality, or probit analysis (LEC 50 ) did not differ among stocks. The 24-hour LEC 50 was 2.34 mg O 2 · L -1 for all stocks combined.     

Wintering bats of the upper Snake River plain: occurrence in lava-tube caves

Distribution and habitat selection of hibernating bats at the Idaho National Engineering Laboratory (INEL) and adjacent area are reported. Exploration of over 30 lava-tube caves revealed that two species, Myotis leibii and Plecotus townsendii, hibernate in the upper Snake River Plain. Five species, M. lucifugus, M. evotis, Eptesicus fuscus, Lasionycteris noctivagans, and Lasiurus cinereus are considered migratory. Myotis leibii and P. townsendii hibernate throughout much of the area, occasionally in mixed-species groups. Myotis leibii uses the dark and protected regions of the cave, usually wedged into tiny pockets and crevices near or at the highest portion of the ceiling. Individuals of P. townsendii may be found at any height or depth in the cave. Temperature appears to be the primary limiting factor in habitat selection. Myotis leibii was found in significantly cooler air temperatures than P. townsendii . Neither species tolerated continuous temperatures below 1.5 C. Relative humidity does not seem to be a significant factor in the distribution or habitat selection of the two species in lava-tube caves.     

Composition and abundance of periphyton and aquatic insects in Sierra Nevada, California, stream

The species composition of periphyton and benthic insect communities and abundances of common taxa (&;gt;0.1&;#37; of individuals) were examined during snow-free months in Convict Creek, a permanent snowmelt- and spring-fed stream in the Sierra Nevada of California. The communities were highly diverse. The most abundant taxa in the periphyton were diatoms ( Achnanthes minutissima, Cocconeis placentula lineata, Cymbella microcephala, C. sinuata, Fragilaria construens, F. crotonensis , Navicula spp., Synedra acus , and S. rumpens ), except in late spring and summer when several seasonal blue-green algae ( Chamaesiphon incrustans, Lyngbya spp. and Oscillatoria spp.) are at their maximum densities. Most common periphyton taxa vary systematically in abundance with season, but relative abundances of taxa also appear to be influenced by streambed scouring and by concentrations of ambient nutrients. Data on population densities and length frequencies of larval and nymphal stages of common benthic insects and occurrences of pupal and adult stages were examined to determine life history patterns. Taxa hatching in winter and spring and abundant as immatures in late spring include ephemeropterans ( Epeorus longimanus, Drunella flavilinea , and Caudatella heterocaudata ), plecopterans ( Calineuria californica, Doroneuria baumanni, and Pteronarcys princeps ) and dipterans ( Cryptolabis sp.). Common taxa hatching in late spring or summer are the plecopteran Malenka ( californica? ) and the trichopterans Arctopsyche grandis and Rhyacophila acropedes . Several bivoltine and multivoltine ephemeropterans ( Baetis devinctus and B. tricaudatus ) and dipterans ( Simulium spp. and Chironomidae) have summer cohorts. Taxa hatching in late summer or autumn and most abundant in autumn include ephemeropterans ( Baetis spp., Ephemerella infrequens, Epeorus dulciana, Ironodes lepidus , and Paraleptophlebia pallipes ), trichopterans ( Hydropsyche oslari, Lepidostoma spp., Glossosoma califica, Micrasema sp., Brachycentrus americanus, Neophylax sp., and Rhyacophila vaccua ) and dipterans ( Antocha monticola, Pericoma sp., and Chironomidae). Major recurring events that may influence life history patterns and structure of the benthic insect community are (1) near-freezing, nighttime winter water temperatures and occasional anchor ice, (2) a prolonged period of high discharge in late spring and early summer (3) a brief summer, and (4) a prolonged period of moderate stream discharge in autumn when the substratum is stable and food is abundant.     

Seed bank dynamics and habitat indicators of Arctomecon californica, a rare plant in a fragmented desert environment

Protection of endangered desert plant species is frequently complicated by a lack of information about seeds, the most stress-resistant and populous life stage. We studied the relative locations of seeds and plants of a rare endangered herbaceous perennial, the Las Vegas bearpoppy ( Arctomecon californica ) in seven 1-ha sites randomly located within a 100-ha study area that was slated for development in Las Vegas, Nevada. We also measured the physical and biological attributes of the environment supporting the seeds and plants, including soil hardness, rock cover, cryptogamic crust cover, and associated vegetation. Arctomecon californica seed density was 0.651 seeds · m –2 , and seeds were found throughout the top 4 cm of soil. Seed viability among sites ranged from 26% to 79%; however, no significant changes between depths were detected. The spatial distribution of the seed bank coincided with the current A. californica adult distribution only in sites with both a high plant density and high numbers of seeds. Arctomecon californica adults occupied open areas within the gypsum environment that supported significantly less vegetative cover than the surrounding area. We observed a positive association between A. californica adults and shadscale ( Atriplex confertifolia ) and a negative association with 7 other plant species among sites. Sites with an indurated abiotic crust hosted higher numbers of A. californica adults than sites with softer soils. However, rock cover, cryptogamic crust cover, and soil hardness were poor explanatory factors for characterizing A. californica presence. We suggest that land managers should incorporate seed bank census into monitoring programs due to the extreme year-to-year fluctuations in A. californica plant population densities. A menudo la protección de especies de plantas desérticas en peligro de extinción se ve complicada por la falta de información sobre las semillas, la etapa de vida más abundante y resistente al estrés. Estudiamos la ubicación relativa de semillas y plantas de “Las Vegas bearpoppy” ( Arctomecon californica ), una planta perenne en peligro de extinción, en 7 sitios de 1 ha. localizados al azar dentro de un área de estudio de 100 ha que estaba destinada a la urbanización en Las Vegas, Nevada (E.U.A.). También medimos los atributos físicos y biológicos del ambiente que sostiene las semillas y plantas, tales como dureza del suelo, rocosidad, cobertura de costra cryptógama y vegetación asociada. La densidad de semillas de A. californica fue 0.651 semillas · m –2 y se observó en los 4 cm superiores del suelo. La viabilidad de las semillas varió del 26% al 79% entre los sitios; sin embargo, no detectamos cambios significativos entre profundidades. La distribución espacial del banco de semillas coincidió con la distribución actual de adultos de A. californica, sólo en sitios que tuvieron una alta densidad de plantas y altos números de semillas. Los adultos de A. californica ocuparon áreas abiertas dentro del ambiente de yeso que sostenía significativamente menos cobertura vegetal que las áreas circunvecinas. Observamos una asociación positiva entre los adultos de A. californica y el chamizo ( Atriplex confertifolia ) y una asociación negativa con siete otras especies de plantas entre sitios. Los sitios con una costra abiótica endurecida albergaron más adultos de A. californica que los sitios con suelos más blandos. No obstante, la cubierta rocosa, la costra cryptógama y la dureza del suelo fueron inadecuadas como factores para caracterizar la presencia de A. californica. Sugerimos que los manejadores de tierras deben incorporar censos de bancos de semillas en los programas de monitoreo, debido a las fluctuaciones extremas de un año a otro en la densidad poblacional de A. californica. Normal 0 MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman";}     

Notes on the white-tailed antelope squirrel, Ammospermophilus leucurus, and the pinyon mouse, Peromyscus truei, in north central Nevada

A four-season live trapping study in the Whirlwind Valley, on the Lander and Eureka county lines near the Humboldt River, yielded two species previously unrecorded from both counties, Ammospermophilus leucurus and Peromyscus truei. Both records represent minimal airline range extension of 113 and 105 km. It is suggested that the distribution of A. leucurus may include the entire northeastern quadrant of Nevada. The occurrence of P. truei in sagebrush habitat 21 km from the nearest pinyon woodland is unusual and suggests that this species may occur patchily distributed throughout the lower elevation ranges in the northern portion of the state.        

Modeling global warming scenarios in greenback cutthroat trout ( Oncorhynchus clarki stomias ) streams: implications for species recovery

Changes in global climate may exacerbate other anthropogenic stressors, accelerating the decline in distribution and abundance of rare species throughout the world. We examined the potential effects of a warming climate on the greenback cutthroat trout ( Oncorhynchus clarki stomias ), a resident salmonid that inhabits headwater streams of the central Rocky Mountains. Greenbacks are outcompeted at lower elevations by nonnative species of trout and currently are restricted to upper-elevation habitats where barriers to upstream migration by nonnatives are or have been established. We used likelihood-based techniques and information theoretics to select models predicting stream temperature changes for 10 streams where greenback cutthroat trout have been translocated. These models showed high variability among responses by different streams, indicating the usefulness of a stream-specific approach. We used these models to project changes in stream temperatures based on 2° C and 4° C warming of average air temperatures. In these warming scenarios, spawning is predicted to begin from 2 to 3.3 weeks earlier than would be expected under baseline conditions. Of the 10 streams used in this assessment, 5 currently have less than a 50% chance of translocation success. Warming increased the probability of translocation success in these 5 streams by 11.2% and 21.8% in the 2 scenarios, respectively. Assuming barriers to upstream migration by nonnative competitors maintain their integrity, we conclude that an overall habitat improvement results because greenbacks have been restricted through competition with nonnatives to suboptimal habitats, which are generally too cold to be highly productive.     

Temperature-related behavior of some migrant birds in the desert

Behavior of migrant birds in relation to temperature was studied and compared to that of resident species in the northern Mojave Desert. Migrants reduced foraging intensity above 30 C, but resident species showed no striking decrease in intensity of foraging at temperatures up to 35 C. Migrant species shifted activities to shaded microhabitats at temperatures between 20 and 30 C; the resident Verdin showed a similar shift at 35 C. Most migrants decreased the amount of time spent foraging at temperatures above 30; Verdins showed a similar but stronger response to temperatures about 30 C. Significant reductions in the use of hovering and hawking maneuvers were found among migrants at temperatures above 30 C. Migrants showed similar types of behavioral adjustments to temperatures as did resident desert species, but they responded earlier in the daily temperature cycle. Desert birds appear to correlate their daily activity strongly with temperature, but nondesert species may respond either to temperature or time of day.     

A plasma protein marker for population genetic studies of the desert tortoise ( Xerobates agassizi )

Fifty-seven individual plasma samples from desert tortoises ( Xerobates agassizi ) representing 10 separate populations were analyzed by polyacrylamide gel electrophoresis using alkaline buffers. An albumin-like protein was found to be polymorphic for two electromorphs in northern populations inhabiting the Mohave Desert Province while Sonoran Desert populations to the south were monomorphic. The genetic divergence demonstrated in this survey is similar to earlier studies and provides evidence for the Colorado River as a potential barrier to gene flow among tortoise populations. These data suggest that tortoise plasma, examined by various electrophoretic methods, may provide a nondestructive means of determining the broad regional origin of desert tortoises.     

Zoogeographic affinities of the stoneflies (Plecoptera) of the Raft River Mountains, Utah

We examined faunal affinities of the Raft River Mountains using stoneflies (Plecoptera) as indicators. This island-like mountain range is isolated from other major mountain ranges in the Intermountain West by low-elevation, arid regions. Thirty-seven species were recorded from collections from 19 sites in the Raft River Mountains. Cluster analysis demonstrated the Raft River Mountain stonefly assemblage to be most similar to faunas of the Sawtooth and Wasatch mountains, and quite different from that of the Sierra Nevada. An analysis of the distribution patterns of each species, on a family-by-family basis, showed that the Raft River Mountains fauna consists mostly of species widespread in western North America. Most families were represented by at least 1 species whose distribution supports faunal affinities with regions to the north and west. Logistic regression of 6 long-distance dispersal factors against stonefly presence-absence data did not support long-distance dispersal as a viable means of colonization for the Raft River Mountains. This suggest that stonefly distribution patterns may be attributed to expansion and subsequent vicariance of suitable stonefly habitats during Pleistocene climatic oscillations.     

Emergence patterns of large stoneflies (Plecoptera: Pteronarcys, Calineuria, Hesperoperla ) in a Montana river

Emergents of Pteronarcys californica, Calineuria californica , and Hesperoperla pacifica were captured with replicated emergence traps at 3 sites along the banks of Rock Creek, Montana. Pteronarcys emergence in early June was short (88% of individuals in 6 d) and attained rates of 5 m -1 d -1 (shoreline distance) and cumulative densities up to 19 m -1 yr -1 . Calineuria emerged synchronously (89% in 9 d) 2 wk later at densities up to 7 m -1 d -1 and 40 m -1 yr -1 . The less numerous Hesperoperla (5 individual m -1 yr -1 ) had a longer emergence period partially coinciding with Calineuria Median males of Pteronarcys and Calineuria emerged 2-3 d before median females; protandry was not significant Hesperoperla . Sex ratios were female-biased in Pteronarcys and Hesperoperla but male-biased in Calineuria . Size trends through emergence were very weak although females showed a greater tendency towered larger size early in emergence.     

Temperature-dependent geographic variation in the flashes of the firefly Luciola cruciata (Coleoptera: Lampyridae)

This study examined the regression of male interflash intervals of Luciola cruciata on ambient air temperatures at five sites in central Japan. The result indicated a significant negative correlation between these two variables at any of the sites. The regression lines varied from site to site and, therefore, the five local populations were classified into three types; the fast-flash, slow-flash, and intermediate types. This classification was supported by molecular biological studies, but contradicted the results of previous ecological studies based on interflash intervals only. My result suggests that first the slow-flash type and then the intermediate type evolved from an ancestral fast-flash type. The geographic variation in flashes of this firefly may have arisen from shifts in the response of male flashes to ambient temperature.     

Humpback chub ( Gila cypha ) in the Yampa and Green rivers, Dinosaur National Monument, with observations on roundtail chub ( G. robusta ) and other sympatric fishes

We evaluated distribution, habitat use, spawning, and species associations of the endangered humpback chub ( Gila cypha ) in the Yampa and Green rivers, Dinosaur National Monument, from 1986 to 1989. Adult and juvenile humpback chub were captured in high-gradient reaches of Yampa and Whirlpool canyons where they were rare ( n = 133, G. robusta ) were widely distributed in eddies, pools, runs, and riffles. Humpback chub ( n = 39) and roundtail chub ( n = 242) in reproductive condition were sympatric in eddy habitats during the 5-6 week period following highest spring runoff. River temperatures at this time averaged about 20 C. Nonnative channel catfish ( Ictalurus punctatus ) were abundant in eddies yielding humpback and roundtail chubs, suggesting a potential for negative interactions between the native and introduced fishes.     

First record of Climacia californica (Neuroptera: Sisyridae) and its host sponge, Ephydatia mulleri (Porifera: spongillidae), from Idaho with water quality relationships

The spongillafly, Climacia californica Chandler, and its sponge host, Ephydatia mulleri (Lieberkuhn), are reported from the state of Idaho for the first time. Climacia californica has not previously been reported from E. mulleri . Collections were made in the Burley – Twin Falls area, and detailed water quality data are provided for the first time for spongillafly larvae. The water quality data also expand the known tolerance limits of E. mulleri for water temperature, conductivity, pH, hardness, silica, and residue.         

Do zebra stripes influence thermoregulation?

The temperatures of black and white stripes on two zebras and a zebra hide were measured, throughout separate sunny days in Kenya. There is a 12–15^oC difference between living zebras’ stripe temperatures throughout the middle seven daytime hours. The hide temperatures reach 16^oC higher than the living zebras. Like all equids, zebras sweat to keep cool. Movement of sweat away from the skin is accelerated by the recently discovered surfactant equid protein latherin, a vital component of cooling in racehorses. Latherin decreases the surface tension of the sweat, facilitating evaporative cooling at the hair tips. We suggest that the abrupt temperature difference between the stripes causes chaotic air movement above the hair surface, thus enhancing evaporative heat dissipation. This cooling mechanism explains the lower temperatures of living zebra stripes than those of the inanimate hide. We observed that the black stripes can be separately erected, while the white remain flat. This may further refine the mechanism. There is an ongoing debate about the function of zebra stripes, recently focussed on the fact that stripes deter biting flies. The data and observations in this paper suggest that the primary function of the stripes may be thermoregulation and a secondary benefit, fly-deterrence.     

Occurrence of native Colorado River cutthroat trout ( Oncorhynchus clarki pleuriticus ) in the Escalante River drainage, Utah

Field surveys were conducted during 1997 and 1998 documenting the distribution and abundance of Colorado River cutthroat trout ( Oncorhynchus clarki pleuriticus ) in Escalante River tributaries. This documented occurrence of native trout in the Escalante River drainage of southern Utah represents an expansion of the known historic range of this subspecies as reported before the 1990s. We found 5 populations of native trout ranging in biomass from 3.0 to 104.2 kg ha -1 and occupying 13.2 km of stream of 130 km of estimated historic habitat. Current distribution and abundance of Colorado River cutthroat trout were compared to early introductions of nonnative trout stocked for sport fishing purposes. Native cutthroat trout have been displaced by nonnative cutthroat trout ( O. c. bouveri ), rainbow trout ( O. mykiss ), brook trout ( Salvelinus fontinalis ), and brown trout ( Salmo trutta ) except where they were isolated by physical or biological barriers. Displacement may have been more extensive except for the remoteness of the drainage and relatively recent introductions of nonnative trout. These conditions limited the overall amount of the drainage stocked, numbers of nonnative trout stocked, and time over which stocking occurred. Discoveries of native trout populations within the Escalante River drainage have allowed expanded conservation of this subspecies by adding new populations to what was known to exist and by increasing the known natural range of this fish.     

Thermal tolerances and preferences of fishes of the Virgin River system (Utah, Arizona, Nevada)

Critical thermal maxima (CTM) and thermal preferenda of the common fishes of the Virgin River were examined. Differences in final temperature preferenda and CTM for species with low thermal lability (speckled dace, spinedace, roundtail chub) correspond well with differences in their distribution and abundance in the river. These species shifted their acute thermal preferences relatively little as acclimation temperature increased. For thermally labile species (woundfin, red shiner, desert sucker, and flannelmouth sucker), the final preferendum is a less precise indicator of probably distribution. The woundfin, an endangered fish, has a high CTM (39.5 C at 25 C acclimation) and a labile species preferendum (slope nearest 1) compared to other species in the system. The introduced red shiner likewise has a high CTM and a labile acute preferendum. In cooler temperatures, its acute preferendum shifts more rapidly than does that of the woundfin. At higher temperatures (above 15 C), the red shiner does not shift its acute preferendum as rapidly as does the woundfin. The red shiner, however, has a higher final preferendum. For thermally labile species, influence of acclimation temperature on mean preferendum, together with CTM, provides a better insight into distributional relationships within the system.     

Parasites of the woundfin minnow, Plagopterus argentissimus , and other endemic fishes from the Virgin River, Utah

Two hundred woundfin minnows, Plagopterus argentissimus , from four sites along the Virgin River, Utah, were examined on two dates during summer 1985. The foreguts of 211 woundfin and variable numbers of other fishes from the Virgin River near Beaver Dam Wash, Arizona, and Mesquite, Nevada, were examined for cestodes on four dates throughout 1979. Seven parasites were found in P. argentissimus: Posthodiplostomum minimum (metacercariae), Diplostomum spathaceum (metacercariae), Bothriocephalus acheilognathi, Gyrodactylus sp., Lernaea cyprinacea, Trichodina sp., and Ichthyophythirius multifiliis . Fungal infections were noted on two fish during the study. Seventeen Virgin River roundtail chub, Gila robusta seminuda, were examined from two of the four sites in 1985 and 64 specimens from Beaver Dam Wash were examined in 1979. Gila robusta seminuda was infected with Posthodiplostomum minimum (metacercariae) and Bothriocephalus acheilognathi, the Asian fish tapeworm. This cestode probably gained entrance into the ichthyofauna of the Virgin River from red shiners, Notropis lutrensis, and has the potential of being very detrimental to the endemic and endangered fishes of the Virgin River. Parasite loads were correlated with water quality and habitat disturbance, with highest number and frequency occurring in "disturbed" sites. Low river flows and increased total dissolved solids appear to be associated with a higher parasite frequency and mean number in fishes of the Virgin River. These data represent the first known published records for parasites of the woundfin minnow and Virgin River roundtail chub.     

Floristics of the upper Walker River, California

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} A checklist of the vascular flora of the upper Walker River is presented. Listed are 1078 taxa from this 4000 km 2 area. The upper Walker River encompasses a portion of the boundary between the Intermountain and Sierra Nevada floristic regions, and hence displays much floristic diversity within a relatively small area. Due to its location along the east slope of the Sierra Nevada, the Walker River drainage is unique in that it contains much elevational variation eastward into the Intermountain Region. This elevational extension is due to the presence of large mountain ranges including the Sweetwater Mountains, the Bodie Hills, and the Wassuk Range. As a result of this elevational variation, there is much overlapping of the two floristic regions. Additionally, the easternmost exposures of the Sierran granodiorites occur within the Walker River basin and may enhance the eastward migration of Sierran plants. The 90 percent floristic similarity (Sorenson’s) between the Sweetwater Mountains, lying to the east of the Sierra, and the east slope of the Sierra Nevada (within the Walker River drainage) indicates the Sweetwaters to be more affiliated with the Sierran flora instead of the Intermountain flora.