Chloroplast ultrastructure in the desert shrub Chrysothamnus nauseosus ssp. albicaulis

Ultrastructure of the chloroplasts of white rubber rabbitbrush ( Chrysothamnus nauseosus (Pallas) Britt. ssp. albicaulis ) was observed with electron microscopy. In addition, leaf anatomy was observed with light microscopy. Previously, it had been reported that the leaves of this desert shrub exhibited a relatively high rate of photosynthesis when compared to other C 3 plants. Comparisons with chloroplasts of other C 3 and C 4 plants demonstrated a reduced amount of granal stacking in the rabbitbrush. However, the classification of rabbitbrush as a C 3 plant is confirmed. RUBP-carboxylase concentration is reported at about 450 mg · ml -1 stromal space based on the estimation of 1 mg of chlorophyll per 25 ul of stromal space in a normal C 3 chloroplast and data from an assay to determine the ratio of RUBP-carboxylase to chlorophyll.     

High rates of photosynthesis in the desert shrub Chrysothamnus nauseosus ssp. albicaulis

  Basic aspects of photosynthesis were investigated in white rubber rabbitbrush ( Chrysothamnus nauseosus (Pallas) Britt. ssp. albicaulis ), a common C 3 deciduous shrub native to arid regions of the western U.S. Under favorable field conditions, net photosynthesis (P n ) ranged from 36 to 73 mgCO 2 · dm – 2 · hr – 1 , which is relatively high for a woody species. The leaves from the actively growing flowering shoots exhibited higher P n than those on the vegetative shoots. P n also varied according to the age of the leaves and the location of the plants. P n did not light saturate even at quantum flux densities (QFD) equivalent to full sunlight. The light compensation point was relatively high (ca 100 μ mol · m – 2 · S – 1 ), perhaps due to the presence of a tomentose vestiture on the leaf surface. At high QFD's, the stomatal conductance was high (ca 520 mmol · m – 2 · s – 1 ) for a woody species. RUBP - carboxylase content of the leaves ranged from 20 to 22 mg per gram F.W., which is similar to that found in most C 3 crop species. These results suggest that rabbitbrush is able to maintain high rates of P n , at least under nonstressed conditions.           

Natural polyploidization within tetraploid and hexaploid populations of the desert shrub Atriplex confertifolia

Shadscale ( Atriplex confertifolia ) is a wind-pollinated dioecious shrub of western North America with an unusual development of apparently autoploid races, showing all even ploidy levels from 2x to 12x (base x = 9). Of these, tetraploid races are the most frequently encountered, with octoploids the next most common, and hexaploids being much less common. In this study, the occurrence of neopolyploid individuals within tetraploid and hexaploid populations of shadscale was examined at natural sites in order to investigate the pathways by which octoploids may be formed and to find a possible explanation for the predominance of octoploids over hexaploids. The frequencies of apparent neopolyploid individuals among adults and the frequencies of their backcrosses were tabulated, as was the occurrence of neopolyploidy among seeds of female plants from some of the same populations. The neopolyploids encountered in these surveys were almost exclusively those expected from unions involving single unreduced gametes. 6x presumed neopolyploid plants were observed in tetraploid populations at a frequency of 0.20%, and 6x seeds were observed at a frequency of 1.91%. Within examined hexaploid populations, 9x adults were not encountered, but 9x seeds were observed at a rate of 0.52%. Evidence was obtained for the operation of some postulated autoploid pathways for generation of octoploids, but these routes did not operate at rates comparable to those for the production of hexaploids. Although the question needs to be studied by genetic methods, the most probable reason for scarcity of hexaploids in nature appears to be that some tetraploid races are diploidized, which would result in irregularities of meiosis in their neohexaploids and a failure to form new races due to infertility and inviability. El “shadscale” ( Atriplex confertifolia ) es un arbusto dioico del oeste de Norteamérica polinizado por el viento que exhibe el desarrollo inusual de razas aparentemente poliploides, con todos los niveles pares de ploidía desde 2x hasta 12x (x base = 9). De éstos, los más comunes son los tetraploides y luego los octoploides. Los hexaploides son mucho menos comunes. En este estudio, examinamos la presencia de individuos neopoliploides entre poblaciones tetraploides y hexaploides del shadscale en sitios naturales para investigar los medios por los cuales se pueden formar los octoploides y para encontrar una posible explicación para el predominio de los octoploides sobre los hexaploides. Tabulamos la frecuencia de individuos aparentemente neopoliploides entre adultos y su descendencia retrocruzada, así como la presencia de neopoliploides entre semillas de las plantas femeninas de algunas de las mismas poblaciones. Los neopoliploides encontrados en estos muestreos fueron casi exclusivamente los que se esperarían de la unión de un gameto no reducido y un gameto reducido. Observamos plantas 6x presunta mente neopoliploides en poblaciones tetraploides con una frecuencia del 0.20%, o del 1.91% en las semillas. Entre las poblaciones examinadas de hexaploides, no encontramos adultos 9x, aunque los observamos con una frecuencia del 0.52% en las semillas. Obtuvimos evidencia de la operación de algunos procesos autoploides postulados para explicar la generación de octoploides, pero estos procesos no operan a frecuencias comparables a aquellas para la producción de hexaploides. Aunque es preciso investigar el tema mediante métodos genéticos, la causa más probable para la escasez de los hexaploides en entornos naturales parece ser que algunas razas tetraploides son diploidizadas, produciendo irregularidades meióticas en sus neohexaploides, los cuales no logran formar razas nuevas debido a su infertilidad o inviabilidad.     

Nest site selection in raptor communities of the eastern Great Basin desert

Measures of niche breadth and overlap were used to compare nest site selection in a community of 10 raptor species and the Raven nesting in the eastern Great Basin Desert. Three variables were examined: nest site type, elevation, and exposure. Results suggest a division of component raptor species into relatively abundant core species that show wide niche breadths and uncommon fringe species with narrow niche breadths. Differences in use of each resource are most pronounced along elevation gradient in which three guilds are evident that correspond to raptor species groupings that nest at higher, middle, and lower elevations. Each guild is comprised of a mix of core and fringe species. Raptor species with highest overlap along one or more nest site variables examined are separated by differences in activity patterns.     

Winter macroinvertebrate communities in two montane Wyoming streams

Macroinvertebrate communities were examined on 4 winter dates over a 4-yr period in 2 high-altitude Rocky Mountain streams to document overwintering assemblages potentially experiencing spring acid pulses. Taxa richness values were comparable to other published lists for alpine and montane stream systems despite the fact that most literature reflected summer collections. Mean benthic density ranged from 1406 to 19,734 organisms/m 2 , and drift rates ranged from 0 to 1740 organisms/100 m 3 . Benthic collections showed higher taxa richness than drift collections while the Ephemeroptera and Plecoptera occurred in greater proportions in drift than in benthos. The Nemouridae (Plecoptera), Ephemerellidae and Heptageniidae (Ephemeroptera), Chironomidae (Diptera), and Hydracarina were the numerically dominant taxa in benthic collections. Grazer/scrapers and shredder/detritivores were always the numerically dominant functional feeding groups at all sites, composing 60-90% of the benthos. Predators, constituting approximately 15% of the community, occurred in the same relative proportion at all sites on all dates. Winter macroinvertebrate communities in these low-order, montane streams exhibit high taxonomic richness and benthic densities as great as lower-elevation mountain streams in the West.     

Tree size and understory phytomass production in a western juniper woodland

Understory phytomass production in a western juniper ( Juniperus occidentalis ) woodland was examined relative to tree size in central Oregon in 1983 and 1984. Vegetation was sampled in two zones, the canopy zone (beneath the canopy) and the intercanopy zone (the space between canopies), on two adjacent sites—a lower slope site with shallow soil and an upper slope site with deeper soil. Sampling was stratified into three tree size classes. Individual species production was significantly affected by tree size and location relative to tree canopy. Production of bottlebrush squirreltail, bluebunch wheatgrass, cheatgrass, miscellaneous annual grasses, perennial forbs, and annual forbs increased with increasing tree size. Sandberg bluegrass production was greater in the intercanopy than the canopy zone, while production of bottlebrush squirreltail, bluebunch wheatgrass, miscellaneous annual grasses, and both perennial and annual forbs was greater in the canopy zone. Production of cheatgrass was determined by the interaction of tree size and zone. Phytomass relationships were expressed to a greater degree on the upper slope site, where total production exceeded that of the lower slope site by approximately 50% the second year of the study. Individual trees appear to exert a great influence on associated vegetation as western juniper woodlands progress from the seedling (tree establishment) phase to closed stands of mature trees. Original community dominants appear to be spatially segregated beneath tree canopies and associated with large trees, while formerly less common species, such as cheatgrass, come to dominate the entire site.     

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";}     

Temporal dynamics of invertebrate and aquatic plant communities at three intermittent ponds in livestock grazed Patagonian wetlands

Ponds are recognized worldwide as biodiversity hotspots; nevertheless in Patagonia studies are still needed that reveal the composition and status of their communities. This paper analyses the temporal patterns of aquatic invertebrates and assesses the environmental factors that best predict the variation in community structure at three small intermittent ponds, subjected to ranching practices (summer stocking) in the Patagonian steppe. Variables identified as important in structuring community assemblages were related to environmental conditions (rainfall and water temperature), chemical features (conductivity and pH) and biotic factors (macrophyte coverage). During the connected phase only a small number of invertebrate species were present, in contrast to the 11 taxa that were frequent and abundant during the isolated period (Eucyclops chilensis, Hyalella curvispina and Rhionaeschna sp. were dominant). In this sequence the submersed Myriophyllum quitense and Lilaeopsis macloviana played a crucial role offering habitat and food resources. The present study provides valuable information that can contribute to minimizing the environmental damage and the development of strategies for the conservation of Patagonian wetlands.     

Competition between harvester ants and rodents in the cold desert

Local distribution patterns of three rodent species ( Perognathus parvus, Peromyscus maniculatus, Reithrodontomys megalotis ) were studied in areas of high and low densities of harvester ants ( Pogonomyrmex owyheei ) in Raft River Valley, Idaho. Numbers of rodents were greatest in areas of high ant-density during May, but partially reduced in August; whereas, the trend was reversed in areas of low ant-density. Seed abundance was probably not the factor limiting changes in rodent populations, because seed densities of annual plants were always greater in areas of high ant-density. Differences in seasonal population distributions of rodents between areas of high and low ant-densities were probably due to interactions of seed availability, rodent energetics, and predation.     

Observations on the distribution of microorganisms in desert soil

Population estimates of fungi, bacteria, and actinomycetes in desert soil were determined with respect to soil depth and distance from shrubs. In general the highest numbers of microbes were found at the shrub base; the lowest numbers were found in the interspaces. While the total number of organisms usually declined in deeper soil, the relative importance of the actinomycetes increased. These population trends are attributed to substrate availability and utilization and interspecific interactions. As the soils became drier and warmer the total number of microorganisms decreased. Mold populations remained at about the same level during the study. While the numbers of both bacteria and actinomycetes declined, the relative importance of the actinomycetes increased.        

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.     

Comparative life history and floral characteristics of desert and mountain floras in Utah

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;} Life forms and floral characteristics of plants at Arches National Park (desert communities), the Mt. Nebo complex, and a subalpine meadow in the Uinta Mountains (montane and subalpine communities) were compared. Characteristics observed were (1) life form, (2) longevity, (3) pollination system, (4) flower structure, (5) flower symmetry, and (6) flower color. Common families in each flora were also compared. Results showed that there is a significant overrepresentation of shrub species at Arches, and an underrepresentation of perennial forbs. Relative number of perennial forb species was significantly higher at Mt. Nebo and the subalpine meadow than at Arches National Park. Native annuals and wind-pollinated species were significantly overrepresented at Arches. Flowers with open structure that permit free access of most insects to nectar and pollen were overrepresented at Mt. Nebo and in the subalpine meadow. The distribution of flower colors also differs significantly among these ecologically contrasting floras, with yellow being best represented in the desert and white in the mountains.       

Mule deer and pronghorn use of wastewater ponds in a cold desert

Pronghorn ( Antilocapra americana ) and mule deer ( Odocoileus hemionus ) were counted at wastewater ponds at the Idaho National Engineering and Environmental Laboratory (INEEL) in southeastern Idaho 4 to 8 times per month from August 1989 through July 1991. Mule deer used wastewater ponds ( n = 15) from June through December and were most commonly observed August through November. Pronghorn frequented wastewater ponds from May through November and were most common from July through September, the driest and warmest months; ponds were also used heavily in November 1990. Diel activity was studied from July through October. Mule deer use of ponds varied in relation to 8 diel time periods in August ( P = 0.02) and September ( P = 0.01) while pronghorn use varied by time period ( P P P < 0.01) August through October. Mule deer and pronghorn use of ponds was not related to distance from site facilities (groups of buildings used for research and other purposes). Pronghorn made greater use of individual ponds lacking additional nearby watering sites, and both pronghorn and mule deer were attracted to ponds with grass/forb and shrub cover around the upland periphery.     

Grazing and passerine breeding birds in a Great Basin low-shrub desert

Densities of passerine breeding birds were compared between four range pastures variously grazed by sheep over a 50-year period. The experimental pastures, located at the Desert Experimental Range in southwestern Utah, included three grazed and one ungrazed. Grazed pastures were each heavily stocked and grazed annually at one of three winter seasons (early, middle, or late). Important structural (physiognomic) and compositional differences existed in the vegetation of the experimental pastures. Horned Larks ( Eremophila alpestris [Linnaeus]), numerically dominant in the pastures, apparently responded to those differences. Black-throated Sparrows ( Amphispiza bilineata [Cassin]) and Loggerhead Shrikes ( Lanius ludovicianus Linnaeus) were less common and found as breeding birds only in dry wash habitats. No significant differences were found between the pastures in estimates of total breeding bird populations, bird standing crop biomass, or bird species richness.     

Vegetation changes after livestock grazing exclusion and shrub control in the southern Chihuahuan Desert

Vegetation cover and production were evaluated after nearly 7 years of livestock grazing exclusion and shrub control in an area with a long history of heavy livestock grazing in the southern Chihuahuan Desert, Mexico. An exclosure was established to prevent livestock grazing. In half of the excluded area, the main shrub, Larrea tridentata , was mechanically controlled. Outside the exclosure, heavy livestock grazing occurred as customary and shrubs were not controlled. Absence of grazing resulted in 50% higher grass cover and 35% higher total biomass. Larrea tridentata cover was twice as high on the grazed area as on the ungrazed area. Vegetation cover was dominated by grasses (42%) in the ungrazed area, whereas in the grazed area, cover was equally divided between grasses (28%) and shrubs (27%). Shrub control did not affect vegetation cover or herbage production. Multivariate analysis confirmed that inside the excluded area, shrub control had little impact on the plant community. The effect of grazing, however, clearly distinguished the community outside the exclosure from that inside the exclosure.     

Classification and ordination of Coleogyne communities in southern Nevada

Woody plant community composition was analyzed throughout the range of Coleogyne ramosissima in the Spring and Sheep Mountain ranges of southern Nevada. The lower Coleogyne elevational boundary was analyzed in detail in Lucky Strike Canyon, on the eastern edge of the Spring Mountains. TWINSPAN (2-way indicator species analysis) identified 4 primary species and stand groups from the 2 mountain ranges (extensive survey). Analysis of DECORANA (detrended correspondence analysis) results indicated that elevation and soil depth were the environmental factors most significantly associated with distribution of species and stand groups in the extensive survey. Elevation was the only significant physical factor associated with distribution of species and stand groups in the intensive survey. Five vegetation zones form the 2 mountain ranges were identified based on their dominant species in 15 extensive transects. Coleogyne were subdivided into pure stands and upper and lower ecotones for further investigation of species distribution and environmental factors. Selected environmental factors appear to play an important role in structuring the Mojave Desert vegetation zones in southern Nevada.     

Influence of soil frost on infiltration of shrub coppice dune and dune interspace soils in southeastern Nevada

The influence of soil frost on the infiltration rate of shrub coppice dune and dune interspace soils was evaluated near Crystal Springs, Nevada, using simulated rainfall. The infiltration rate of the coppice dune soil was greater than the dune interspace soil under frozen or unfrozen conditions. Because of different vegetation cover and surface soil characteristics, coppice dune and dune interspace soils responded differently to freezing, thus imposing a spatial and temporal response to infiltration rate. Infiltration rate of soils with porous concrete frost increased as the soils thawed during simulated rainfall, but soils with nonporous concrete frost allowed very little infiltration to occur. Both coppice dune and dune interspace soils that were classified in January as having granular frost had a higher infiltration rate than the same unfrozen soils in March.     

Effects of arthropods on root:shoot ratio and biomass production in undisturbed and modified mountain shrub habitats

In 1987 the effects of arthropods on root:shoot ratios and biomass production were examined in southeastern Wyoming mountain shrub habitats that were undisturbed or had undergone conventional shrub management by mowing, burning, or herbicide application during the previous year. In habitats with and without shrub canopy, treatment with insecticides generally increased foliage biomass and consistently decreased root biomass, regardless of the shrub management practice. In open areas the effects of insecticide treatments on the root and shoot biomass were relatively greater in undisturbed plots than in any of the managed plots. With only one exception, the root:shoot ratio increased following application of insecticide.     

Secondary production estimates of benthic insects in three cold desert streams

We studied aquatic insect production in three cold desert streams in southeastern Washington. The size-Frequency (SF) and P/B methods were used to assess production, which is expressed by taxon, functional group, and trophic level. Dipterans (midges and black flies) were the most productive taxa, accounting for 40-70% of the total insect production. Production by collectors and detritivores was the greatest of all functional groups and trophic levels, respectively, in all study streams. Insects with rapid development times and multiple cohorts are very important in cold desert streams; they were major contributors to the total insect production. Total insect production rates in our study streams (14-23 g DW·m -2 ·yr -1 ) were greater than those found in Deep Creek, Idaho (1.2 g DW·m -2 ·yr -1 ), the only other cold desert stream for which production data are available. Our values also were generally greater than published data for most cold/mesic (3-27 g DW·m -2 ·yr -1 ) and humid/mesic (3-25 g DW·m -2 ·yr -1 ) streams, but lower than in Sonoran Desert Streams (>120 g DW·m -2 ·yr -1 ) or New Zealand streams (～40 g DW·m -2 ·yr -1 ). Our data support the contention of others that production, rather than density or biomass, is the most accurate and meaningful way to assess the role of these organisms in lotic ecosystems.     

Viability of seed from thirty-two shrub and forb species through fifteen years of warehouse storage

Germination results were obtained from seed stored in an open warehouse in Sanpete County, Utah, over a 15-year period for 18 shrub and 14 forb species. Seed viability was not appreciably affected for 14 species stored at least 15 years. Seed viability did, however, significantly decrease for two species stored 10 years, for five species stored 7 years, for seven species stored 5 years, for three species stored 4 years, and for one species stored only 3 years.