Monitoring with a modified Robel pole on meadows in the central Black Hills of South Dakota

This study using a modified Robel pole was conducted in the central Black Hills, South Dakota. The objectives were to test the relationship between visual obstruction readings and standing herbage, develop guidelines for monitoring, and estimate sample size. The relationship between visual obstruction and standing herbage was linear with 2 segments in a piecewise model. Regression coefficients were highly significant ( P ≤ 0.001). Standard error of the estimate for a single mean was 373 kg ? ha –1 . Herbage ranged from 89 to 3821 kg ? ha –1 with a mean of 1416 kg ? ha –1 . The average number of visually obstructed bands was 6.4 and ranged from 0.21 to 20.4. Cluster analyses grouped the visual obstruction readings into 3 management categories: short, medium, and tall. A minimum of 3 transects (20 stations per transect) is recommended for monitoring areas ≤259 ha (1 section) to be within 20% of the mean at 80% confidence. The protocol developed to monitor standing herbage is accurate, precise, and easy to apply. This tool provides pertinent information for managers to develop guidelines based on the bands and/or standing herbage for monitoring livestock and wildlife use.     

Prairie dog colony attributes and associated vertebrate species

A survey of colony attributes and associated vertebrates on black - tail ( Cynomys ludovicianus ), Gunnison's ( C. gunnisoni ), and white - tail ( C. leucurus ) prairie dogs was made. A belt transect 1.6 km wide and 13,334 km long from Hobbs, New Mexico, to the Utah - Wyoming state line was surveyed. There were 47 colonies located (4760 ha comprising 2.2 percent) in the belt. Intercolony distances varied significantly. Three black - tail towns averaged 33 ha in area (SD = 26, range 10 – 61), II Gunnison's averaged 46 ha (SD = 43, range 16 – 150), and 33 white - tail towns averaged 125 ha (SD = 200, range 0.2 – 958). Badger activity was positively and significantly correlated to colony size and number of burrow openings on Gunnison's and white - tail towns. There were 107 vertebrate species and subspecies (one amphibian, 25 reptiles, 51 birds, 30 mammals) observed on prairie dog colonies. Results of our surveys are compared with prairie dog studies elsewhere. The role of prairie dogs and relationships to some vertebrates species are discussed.     

Pocket gophers ( Thomomys talpoides ) in successional stages of spruce-fir forest in Idaho

This study examined (1) the relative abundance of the pocket gopher ( Thomomys talpoides ) in four successive stages (1–10, 11–39, 40–79, and 80+ years following disturbance) of spruce-fir forest; (2) the relationship between number of gopher sign (mounds and earth plugs) with gopher density; and (3) a method of sampling pocket gopher populations using a 500 by 4 m strip transect. The number of gopher mounds was significantly correlated with the number of earth plugs. Data were pooled and a categorical log linear analysis used to test for significant differences in pocket gopher sign between the four successive stages. The 1–10 and the 80+ -year-old sites had significantly more gopher sign than the 11–39 and the 40–79 year-old sites. No significant differences were found between the 11–39 and the 40–79-year-old sites, or between the 1–10 and the 80+ -year-old sites. The difference in population densities may be due to understory vegetation differences between the successional stages. There was a significant correlation between amount of gopher sign and gophers caught in each of the study sites. This indicates that counts of pocket gopher sign may be used to estimate pocket gopher density. The strip transect is recommended as the most appropriate method when sampling heterogeneous habitats or when there is cause to suspect gopher populations may be aggregated within the area rather than spaced randomly or regularly.     

Black-tailed prairie dog population dynamics at Scotts Bluff National Monument, Nebraska: a 28-year record

Black-tailed prairie dogs, Cynomys ludovicianus, now inhabit a small fraction of their original range in the Great Plains. We monitored a population of black-tailed prairie dogs at Scotts Bluff National Monument, Nebraska, from colonization in 1981 until 2009 (28 years). Colony boundaries were mapped by delineating clip lines and active burrows; population densities were estimated via visual counts. Estimates of total population size revealed 4 distinct periods of changing dynamics: (1) a linear increase, (2) a decline and prolonged depression, (3) an exponential increase, and (4) a period of high variability. Area occupied revealed similar, although less-defined trends, whereas densities fluctuated greatly (8–80 individuals · ha –1 ). Even after almost 30 years, this population remains relatively small. Decreases in the population may have been due, in part, to predation by badgers, although sylvatic plague cannot be ruled out. Black-tailed prairie dogs are recognized as keystone grassland species, and attempts are underway to reintroduce them to parts of their historic range. Our data suggest that black-tailed prairie dogs possess high potential for rapid population growth and decline, regardless of colony size. Therefore, either human-assisted or natural dispersal events may be important in establishing colonies in suitable habitat. El perrito de pradera de cola negra, Cynomys ludovicianus, habita en una pequeña fracción de su distribución original en las Grandes Llanuras. Monitoreamos una población de perritos de pradera de cola negra en Scotts Bluff National Monument, Nebraska, por 28 años, desde la colonización en 1981 hasta 2009. Trazamos los límites de las colonias usando de referencia las líneas de ramoneo y las madrigueras activas, y estimamos la densidad de las poblaciones mediante un recuento visual. Los estimados de población total revelaron cuatro períodos distintos de dinámicas cambiantes: (1) un aumento lineal, (2) una disminución y depresión prolongada, (3) un aumento exponencial y (4) un período de alta variabilidad. El área ocupada reveló tendencias similares, aunque menos definidas, mientras que las densidades fluctuaron mucho (8–80 individuos · ha –1 ). Aún después de casi 30 años, esta población permanece relativamente pequeña. Los decrementos en la población pueden haber sido provocadas en parte por la depredación por tejones, aunque no se puede descartar como causa la plaga silvática. El perrito de pradera de cola negra se considera una especie clave de la pradera, y están en proceso esfuerzos por reintroducirlos en partes de su distribución histórica. Nuestros datos indican que los perritos de pradera de cola negra tienen alto potencial de crecimiento y disminución de su población, sin importar el tamaño de la colonia. Por lo tanto, los eventos de dispersión, ya sean naturales o con asistencia humana, podrían ser importantes para establecer colonias en hábitats adecuados.     

Composition of forest stands used by White-headed Woodpeckers for nesting in Washington

In this study, I examined the composition of managed ponderosa pine ( Pinus ponderosa ) forests used by nesting White-headed Woodpeckers ( Picoides albolarvatus ) along the eastern slope of the Cascade Range in Washington. I sampled trees and snags using the point-centered quarter method to assess species composition, tree and snag density, and stand basal area in 16 forest stands containing White-headed Woodpecker nests. All stands had a history of timber management and 2 had been burned and salvage-logged. Mean live-tree density (≥10.16 cm dbh) was 182.3 trees · ha –1 (SE = 13.52), mean snag density (≥10.16 cm dbh) was 11.5 snags · ha –1 (SE = 1.92), and mean stand basal area was 17.2 m 2 · ha –1 (SE = 1.58). Ponderosa pine had the highest importance value (mean = 220.9, SE = 17.25) of any tree species in all but 2 stands. Mean dbh of ponderosa pines was 33.0 cm (SE = 0.26) and ranged from 26.1 to 50.2 cm within stands. Mean density of ponderosa pine was greatest in the 20.3–30.5 cm dbh size class and lowest in the 50.8–61.0 cm and >61.0 cm dbh size classes. Tree density was up to 5.3 times greater than densities believed to be typical of ponderosa pine forests prior to fire suppression. Snag densities were within the range estimated for historical dry forests of the eastern Cascades, yet only 50% of all snags sampled had a dbh >25.4 cm. Although White-headed Woodpeckers are considered strongly associated with old-growth ponderosa pine, my results suggest that they may be more adaptable to using forests dominated by smaller diameter trees. En este estudio, examiné la composición de los bosques manejados de pino ponderosa ( Pinus ponderosa ), utilizados para anidamiento por el pájaro carpintero cabeciblanco ( Picoides albolarvatus ), a lo largo de la vertiente oriental de la cordillera Cascade del Estado de Washington. Muestreé árboles vivos y muertos usando el método de cuadrantes al punto central en 16 rodales con nidos del pájaro carpintero cabeciblanco para evaluar la composición de especies, la densidad de árboles vivos y muertos y el área basal del rodal. Todas las áreas tenían una historia de manejo maderable y 2 habían sido quemadas y taladas para recuperar madera. La densidad promedio de árboles vivos (≥10.16 cm DAP) fue 182.3 árboles · ha –1 (DE = 13.52), la densidad promedio de árboles muertos (≥10.16 cm DAP) fue 11.5 árboles muertos · ha –1 (DE = 1.92) y el área basal promedio de los rodales fue 17.2 m 2 · ha –1 (DE = 1.58). El pino ponderosa tuvo el valor de importancia más alto (promedio = 220.9, DE = 17.25) de las especies de árboles en todos, menos 2 rodales. El DAP promedio de los pinos ponderosa fue 33.0 cm (DE = 0.26) y variaba de 26.1 a 50.2 cm dentro de rodales. La densidad promedio del pino ponderosa fue la mayor en la clase de 20.3–30.5 cm DAP y menor de las clases de 50.8–61.0 cm y >61.0 cm DAP. La densidad de árboles fue hasta 5.3 veces mayor que las consideradas típicas para bosques de pino ponderosa antes de la intervención para prevenir incendios. Las densidades de árboles muertos estuvo dentro del rango estimado para los bosques secos históricos del oriente de la cordillera Cascade, no obstante sólo 50% de los árboles muertos muestreados tuvieron un DAP >25.4 cm. Aunque se considera que los pájaros carpinteros cabeciblancos están estrechamente asociados con bosques primarios de pino ponderosa, mis resultados sugieren que podrían ser más adaptados a usar bosques donde predominan árboles de diámetro menor.     

Some spatial and behavioral features of the thirteen-lined ground squirrel

Some relationships between home range, agonistic behavior, and reproductive patterns in thirteen-lined ground squirrels were investigated in Laramie Plains, Wyoming (August 1966–April 1969). Population size and densities fluctuated seasonally and annually. Adult male (N = 7) home ranges averaged 0.24 ha and were smaller than those of the female (N = 9), which averaged 0.35 ha. Agonistic interactions were more frequent during the natal period (late May–June) than during the breeding-gestation period (mid April–May). Most squirrels (86 percent) shared capture sites and had overlapping home ranges. However, a certain degree of spacing existed because of agonistic behavior.     

Evaluating the relationship between mule deer pellet-group data and available winter range, using LANDSAT imagery

In this study, mule deer population trend data (deer-days-use/hectare) were statistically analyzed with range area data that were extracted from LANDSAT satellite imagery. The remote sensing techniques developed use multidate, winter images of an area in central Utah. Snow-covered areas and vegetational areas mapped from the imagery were composited into 26 maps representing the approximate winter range available to mule deer on 26 dates over a five-year period (1972–1977). Utah State Division of Wildlife Resources pellet-group transect data were statistically analyzed with range data measured from the satellite imagery. Range area accounted for a fairly large proportion of the variation in deer-days-use/hectare (r = –.83). This result seems reasonable since deer population density should increase as available range decreases.     

A reconnaissance of small mammal communities in Garland and Government prairies, Arizona

Small mammals play key ecological roles in grassland ecosystems, yet little is known regarding small mammal communities in large (>50 km 2 ), high-elevation prairies embedded in ponderosa pine ( Pinus ponderosa ) forests in north central Arizona. To provide information on community composition and habitat relationships, we live-trapped small mammals on 6 transects in 2 prairies in 2008. We captured 78 individuals in 5501 trap occasions. Capture rates were low and varied widely among transects. Community composition was simple, with only 3 species of small mammals captured. In order of relative abundance, these species were deer mouse ( Peromyscus maniculatus, n = 44 individuals), Mogollon vole ( Microtus mogollonensis, n = 22), and spotted ground squirrel ( Spermophilus spilosoma, n = 12). Deer mice were captured on all transects and voles on all but one transect. In contrast, spotted ground squirrels were captured on only 2 transects and were relatively common on only one transect. There were no previous records of spotted ground squirrels in these prairies. Deer mice were positively associated with rock cover and vegetation height. Voles were positively associated with shrub cover and combined cover of live and dead vegetation and were negatively associated with bare ground. Spotted ground squirrels were positively associated with forb cover. This study provides baseline data on small mammal communities in these prairies and documents the presence of a previously unknown species. Further studies would be desirable to better understand spatial and temporal variation in these communities, habitat relationships, and effects of land-use practices on small mammals and their habitats. Los mamíferos pequeños desempeñan papeles clave en los ecosistemas de pradera; sin embargo, se conoce poco con respecto a las comunidades de pequeños mamíferos en las grandes (>50 km 2 ) praderas altas, rodeadas por bosques de pino ponderosa ( Pinus ponderosa ) en la parte norte central de Arizona. Para proporcionar información sobre la composición de las comunidades y sus relaciones con el hábitat, colocamos trampas para pequeños mamíferos vivos en 2008 en 6 transectos en 2 praderas. Capturamos 78 individuos en 5501 ocasiones de trampeo. Las tasas de captura fueron generalmente bajas y variaron ampliamente entre transectos. La composición de las comunidades fue simple, con tan solo 3 especies de mamíferos pequeños capturados. Éstas fueron, en orden de abundancia relativa, el ratón ciervo ( Peromyscus maniculatus, n = 44), el metorito Mogollon ( Microtus mogollonensis, n = 22) y la ardilla moteada de tierra ( Spermophilus spilosoma, n = 12). Los ratones ciervo fueron capturados en todos los transectos y los metoritos en todos, menos uno. En contraste, las ardillas moteadas de tierra fueron capturadas sólo en 2 transectos y fueron relativamente comunes en sólo uno. No había registros anteriores de ardillas moteadas de tierra en estas praderas. Los ratones ciervo estuvieron asociados positivamente con la rocosidad y la altura de vegetación. Los metoritos estuvieron asociados positivamente con la cobertura de arbustos y la cobertura combinada de vegetación viva y muerta, y asociados negativamente con el suelo desnudo. Las ardillas moteadas de tierra estuvieron asociadas positivamente con la cobertura de maleza. Este estudio proporciona datos de referencia sobre las comunidades de pequeños mamíferos en estas praderas, y documenta la presencia de una especie previamente desconocida. Sería conveniente llevar a cabo estudios adicionales para entender mejor la variación espacial y temporal en estas comunidades, sus relaciones con el hábitat y los efectos de prácticas del uso del suelo en equeños mamíferos y sus hábitats.     

Role of livestock and black-tailed jackrabbits in changing abundance of Kochia americana

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;} Historical accounts and matched photographs indicate sharp decline of once-abundant Kochia americana in eastern Great Basin vegetation since the early 1900s, most of the decline by the late 1950s. Exclosure data show further decline from 1957 to 1973, then some increase between 1970 and 1973 and 1976 and 1981. Utah sheep numbers, at maximum from 1925 to 1940 and declining steadily to the 1970s, may have induced the long-term changes. Black-tailed jackrabbits ( Lepus californicus ), could not have induced vegetation decline, but could have added to livestock pressure and abetted the trend. In 1972, rabbits near a cyclic high were indirectly estimated to completely utilize K. americana in Curlew Valley, northwestern Utah. In 1976–1977 at rabbit low, direct measurements show 4%–18% of plants browsed by late summer, about 30%–50% of herbage removed from browsed plants. The latter rose to 45%–82% by end of winter. Late-summer percent browsed may have risen slightly (11%–21%) in 1980–1981 at next rabbit high. Increase in K. americana density from 1973 to 1976, then a slight decrease from 1976 to 1980, suggests fluctuating K. americana abundance induced by rabbit browsing, superimposed on long-term K. americana decline and recovery.     

Tree densities on pinyon-juniper woodland sites in Nevada and California

The densities of sing le leaf pinyon and Utah juniper trees in four diameter classes (1–9, 10–19, 20–29, and ≥ 30 cm) were measured on 522 plots of 1/10 ha each throughout the Great Basin. Density distribution patterns of pinyon and juniper varied with aspect, elevation, and eastern (EGB) versus western Great Basin (WGB) locations. On most locations north and, to a lesser extent, west slopes supported higher densities of pinyon than south and east slopes, with high relative densities of small diameter trees on north slopes and large diameter trees on west slopes. Pinyon densities were higher on EGB than on WGB sites and on higher elevation than on lower elevation sites. Juniper densities were higher on EGB than on WGB sites and on lower elevation than on higher elevation sites. Juniper densities on low-elevation WGB sites were higher on south and west aspects than on north and east, with higher relative densities in the 20–29 cm diameter class than in other diameter classes. On low elevation EGB sites, east and south slopes supported higher juniper densities than did north and west slopes, with comparatively higher relative densities in the 10–19 cm diameter class. Differences in relative densities between diameter classes were not significant among aspects on high elevation sites.     

Short-term effects of logging on red-backed voles and deer mice

Clearcutting and selective logging effects on red-backed voles ( Clethrionomys gapperi ) and deer mice ( Peromyscus maniculatus ) were studied (September–November, 1975; June–October, 1976) in Bridger-Teton National Forest, Wyoming. Five selective cuts (total 137 ha) removed 57 percent (range 34–74 percent) of the trees. One clearcut (9.6 ha) eliminate 84 percent of the trees. Soils remained mesic in selective cuts, but became xeric in the clearcut. Snap-trapping indicated that voles were most abundant on the unlogged and selectively cut mesic sites (76 percent of 408 captures), whereas deer mice were more common on the xeric clearcut (80 percent of 60 captures). Species composition remained unchanged on selective cuts following logging (77 percent voles of 256 captures), but changed from predominantly voles to mostly deer mice (80 percent of 60 captures) in the clearcut. Intraspecific age and sex ratios, litter sizes, and morphological measurements were compared between logged and unlogged areas.     

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";}     

Effects of osmotic potential, potassium chloride, and sodium chloride on germination of greasewood ( Sarcobatus vermiculatus )

Greasewood ( Sarcobatus vermiculatus [Hook.] Torr.) (Chenopodiaceae) typically grows on salt-affected soils where its germination requirements may reflect characteristics necessary for establishment in saline environments. The objective of this study was to determine the effect of osmotic potential and specific ions on the germination of seeds from three populations of greasewood. Seeds were germinated at 20 C in solutions of polyethylene glycol with water potentials ranging from –0.3 to –2.2 MPa that contained 0 to 68480 µmol·L –1 sodium chloride (NaCl) or 0 to 53640 µmol·L –1 potassium chloride (KCl). Germination of two populations was reduced by increasing salt concentration and decreasing osmotic potential; germination of one population was reduced by declining osmotic potential. No seeds germinated at an osmotic potential lower than –1.6 MPa. For all populations, days to 50% of final germination increased and abnormal germination decreased as osmotic potential declined. Comparison of our results with those from other studies suggests geographic ecotypic development in response to osmotic potential and NaCl and KCl concentrations during germination.     

Growth and development of the western harvest mouse, Reithrodontomys megalotis megalotis

Growth rates, gestation period, litter size, reproductive age, sex ratios, and development were studied on 198 litters of Reithrodontomys megalotis megalotis (Baird). Growth was characterized by several standard skull and body measurements and was partitioned into four phases of 1 – 3, 4 – 12, 13 – 22, and 23 – 70 days. Growth was best described by measurements of tail length, ear length, and dried eye - lens weight. Reproductive activity began as early as 38 days for females and 59 days for males. The gestation period was 22 days, and the mean litter size was 3.83 (range 1 – 7). Sex ratio was 53.49 percent males to 46.51 percent females. Reproductive efficiency was 53.53 percent. The development of R. m. megalotis was very similar to that of R. m. dychei. Early breeding, postpartum estrous, year - round breeding, high reproductive efficiency, and a short gestation period contribute to a high reproductive potential in R. m. megalotis.       

Age, growth, and food habits of tui chub, Gila bicolor, in Walker Lake, Nevada

At Walker Lake, Nevada, tui chub were collected 1975–1977 for analysis of age, growth rate, and food habits. The fork length (FL) – scale radius (SR) relationship was linear and described by the equation FL = 4.44 + 3.17 (SR). Age I, II, III, and IV chub were 116, 176, 218, and 242 mm fork length, respectively. Maximum longevity was six years. The length weight relationship was defined by the log transformed linear equation log weight = - 4.65 + 2.93 (log FL). Chub collected from pelagic regions ate mostly zooplankton, whereas chub collected from littoral areas had a diet of zooplankton and benthic organisms.         

Seed germination characteristics of Chrysothamnus nauseosus ssp. viridulus (Astereae, Asteraceae)

Rubber rabbitbrush ( Chrysothamnus nauseosus [Pallas] Britt. ssp. viridulus ) may prove to be a source of high-quality cis-isoprene rubber, but its establishment is limited by a lack of information on seed germination. Consequently, seeds were germinated at alternating temperatures (5–15, 5–25, 15–25, and 20–30 C) in light and dark as well as constant temperatures (15–40 C with 5-C increments) to determine temperature response. Seeds were also germinated in solutions of polyethylene glycol 6000 (0 to –5 bar), salinity regimes (1, 17, 51, and 86 mM) at all the above-mentioned temperatures to determine salinity and temperature interaction. The hormones GA 3 (0, 2.9, 29.0, and 58.0 um) and kinetin (0, 4.7, 23.5, and 47.0 um) were used to study their effect on overcoming salt- and temperature-induced germination inhibition. Seeds of C. nauseosus ssp. viridulus were very sensitive to low temperature. Best germination was achieved at 25 and 30 C, but these seeds also germinated at a higher temperature (35 C). The seeds of rabbitbrush germinated at both constant and alternating temperatures. Light appears to play little or no role in controlling germination of the seeds of rubber rabbitbrush. However, seeds of rabbitbrush were sensitive to salinity, and seed germination was progressively inhibited by increase in salt concentration, although a few seeds still germinated at the highest saline level. Progressively higher concentrations of polyethylene glycol also progressively inhibited germination. Suppression of seed germination induced by high salt concentrations and high temperatures can be partially alleviated by the application of either GA 3 or kinetin.     

Conservative and moderate grazing effects on Chihuahuan Desert wildlife sightings

Seasonal wildlife observations were made along transects on 2 pastures conservatively grazed (36% use of perennial grasses) and 2 pastures moderately grazed (47% use of perennial grasses) in south central New Mexico in non-drought (1997) and drought years (1998). Experimental pastures were similar in soils, terrain, spacing of watering points, and brush cover. Average ecological condition score for the conservatively grazed pastures was 60% compared with 64% for moderately grazed pastures. Throughout the study total standing vegetation understory herbage levels were higher ( P P > 0.05) between conservatively and moderately grazed pastures. Black-tailed jackrabbit ( Lepus californicus ) sightings were higher ( P Antilocapra americana ), scaled quail ( Callipepla squamata ), mourning doves ( Zenaida macroura ), and desert cottontails ( Sylvilagus auduboni ) showed no differences ( P > 0.05) between conservatively and moderately grazed pastures. Dry conditions in 1998 depressed total wildlife sightings by > 50% compared to 1997. Both songbird and gamebird (particularly mourning dove) sightings were severely reduced in the dry compared to wet year ( P < 0.05). Our results are consistent with Nelson et al. (1997) that livestock grazing at intermediate levels had no effect on most Chihuahuan Desert upland wildlife species, and that drought years severely depress wildlife sightings.     

Population ecology and reproduction of the Mexican mud turtle ( Kinosternon integrum ) in Tonatico Estado De México

Ecological data directly from the field are important in understanding the life history strategies of kinosternid species in the tropics. Herein we summarize the basic population ecology and life history of Kinosternon integrum in the municipality of Tonatico (southeastern Estado de M&eacute;xico, M&eacute;xico). From October 2003 to November 2004, we marked a total of 204 turtles and recaptured 118 of them. Mean population size using the Jolly-Seber model was 197 (95% CI 128&ndash;416) individuals, with a sex ratio of 1:1.7, biased to females. Males were larger than females in carapace length and plastron length. The reproductive season starts in late June and finishes in late October. The smallest female with oviductal eggs was 122 mm in carapace length. Mean clutch size was 4 eggs ( s = 1.77, range 1&ndash;8) and was significantly and positively related to body size. Mean egg length was 30.43 mm ( s = 2.24, range 23.92&ndash;35.96), mean width was 16.35 mm ( s = 1.01, range 12.99&ndash;18.30), and mean weight was 5.14 g ( s = 0.60, range 3.41&ndash;6.57). Mean egg length was significantly and inversely related to clutch size. Relative clutch mass (reproductive effort) was 0.043 ( s = 0.017, range 0.017&ndash;0.071), which is the smallest value reported for the genus Kinosternon. Additionally, there was no evidence of a pelvic restriction on egg size in this population. This is the first study that documents basic population ecology and reproductive characteristics for a single population of the most widespread freshwater turtle in Mexico.     

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

&nbsp; 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 &middot; dm &ndash; 2 &middot; hr &ndash; 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 &mu; mol &middot; m &ndash; 2 &middot; S &ndash; 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 &middot; m &ndash; 2 &middot; s &ndash; 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. &nbsp;&nbsp;&nbsp; &nbsp;     

Distribution and abundance of pelagic fish in Lake Powell, Utah, and Lake Mead, Arizona-Nevada

Pelagic fish communities (waters with depths > 20 m) of Lakes Powell and Mead were examined quarterly from 1995 to1998 using vertical gill nets and a scientific echosounder. Nets captured a total of 449 fish consisting of striped bass (57%/45% [Lake Powell/Lake Mead]), threadfin shad (24%/50%), common carp (15%/4%), walleye (3%), channel catfish (2%), and rainbow trout ( -1 ). Reservoirs experienced dramatic seasonal and annual fluctuations in pelagic biomass. Lake Powell's biomass peaked at the Colorado River at 709.7 (± 46.5) kg · ha -1 and Lake Mead's reached 291.9 (± 58.2) kg · ha -1 at Las Vegas Wash. These locations supported estimated fish densities of 124,668 fish · ha -1 and 15,131 fish · ha -1 , respectively. Maximum reservoir biomass peaked in August 1996, with Lake Powell supporting 10,852,738 ± 5,195,556 kg (27.6 × 10 7 fish) and Lake Mead 1,926,697 ± 892.994 kg (10.8 × 10 7 fish). Biomass ebbed in May (1996 and 1997), when Lake Mead supported 65% (296,736 kg vs. 453,097 kg) and 62% (101,016 kg vs. 162,262 kg) of biomass levels found in Lake Powell.