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41.
We describe a case study evaluating the ecological impact of Bromus tectorum L. (cheatgrass) invasion following fire disturbance and the effectiveness of revegetation as a means of rehabilitation in a degraded semiarid shrubsteppe system. The effectiveness of rehabilitation efforts was assessed relative to arthropod richness, vegetation and arthropod community composition, and ground-cover characteristics in 3 habitats: undisturbed, burned and weed infested ( B. tectorum ), and burned then rehabilitated with native and nonnative vegetation. Arthropods were collected in each habitat using pitfall traps. Differences in arthropod richness were compared using rarefaction curves. Nonmetric multidimensional scaling and nonparametric multivariate statistical procedures, including analysis of similarity and similarity percentage routines, were used to compare arthropod and vegetation community composition and ground-cover characteristics between habitats. Arthropod communities in the rehabilitated habitat were distinct from those observed in the undisturbed and weed-infested habitats. Rehabilitation in this study resulted in a shift toward conditions observed in an undisturbed habitat and perhaps is an intermediate step to complete restoration. Arthropod richness, arthropod and vegetation community composition, and ground-cover characteristics were all useful indicators but returned slightly different results. Assessing multiple variables yielded the most complete understanding of the habitats studied. 相似文献
42.
We examined optimal temperatures for growth and the upper thermal tolerance of juvenile northern leatherside chub ( Lepidomeda copei ). We conducted 2 experiments using the acclimated chronic-exposure method to estimate optimal temperature for growth of age-0 northern leatherside chub (range 12.8–28.3 °C). Upper thermal tolerance was estimated using the critical thermal maximum (CTM) and upper incipient lethal temperature (UILT) methods for fish acclimated at 15, 18, 23, and 28 °C. We also measured stream temperatures in Yellow Creek, Summit County, Utah, during July–August 2006 to compare our results to actual summer stream temperatures. Survival in growth tests was not significantly different between treatment temperatures in either experiment (P > 0.098). The optimal temperature for growth in the 1st trial estimated from the 2nd-order polynomial regression was 23.0 °C, falling outside the range of experimental temperatures (12.8–22.2 °C). The estimated optimal temperature for growth in the 2nd trial was 23.2 °C. In the upper thermal tolerance tests, juvenile northern leatherside chub had CTM values between 29.6 and 35.0 °C; CTM values increased as acclimation temperature increased. Upper incipient lethal temperatures (LT50) ranged from 26.5 to 30.2 °C, increasing with acclimation temperature. Summer stream temperatures in Yellow Creek had a lower mean (14.0–18.1 °C) than did the optimal temperature for growth determined in these studies, but these temperatures exhibited diel fluctuations as large as 15.7 °C. 相似文献
43.
44.
Variation in kit fox ( Vulpes macrotis ) population parameters can be influenced by vegetative cover and the distribution and abundance of other predator and prey species. Dramatic changes to Great Basin Desert habitats, which can potentially impact mammalian species, have occurred in some areas in Utah. We examined kit fox demographics and prey populations from 1999 to 2001 on Dugway Proving Ground (DPG), a U.S. Army facility in Utah, and compared some parameters to historical levels (1956–1958, 1966–1969). Adult survival rates were fairly consistent between 1999 and 2000 and between 1999 and 2001; however, survival was greater in 2001 than in 2000. Reproductive rates ranged from 1.0 to 3.8 pups per female in 1999–2000 and were similar to historical numbers (1.0–4.2 pups per female). We found a decrease in pre-whelping kit fox density from the 1960s (0.12 foxes ? km –2 ) to 1999–2001 (0.04 foxes ? km –2 ); however, densities were similar between the current study and the 1950s (0.08 foxes ? km –2 ). Using 9 years of data, we found density dependence between reproductive rates of the current year and annual fox density from the previous year. Using 7 years of data, we found a slight correlation between kit fox annual density and a 1-year lag in leporid abundance, even though leporid abundance was lower during the present study than it was historically. Compared to historical levels, current small mammal abundance and species composition has changed in several habitats. Kit fox breeding density and annual density were inversely correlated with coyote ( Canis latrans ) density. Changes to the landscape at DPG, especially due to invasion of cheatgrass ( Bromus tectorum ) and addition of artificial water sources, have caused a change in available kit fox habitat and prey species, and have increased the abundance of coyotes, the kit fox's major competitor. 相似文献
45.
Common variants at MS4A4/MS4A6E, CD2AP, CD33 and EPHA1 are associated with late-onset Alzheimer's disease 总被引:1,自引:0,他引:1
Naj AC Jun G Beecham GW Wang LS Vardarajan BN Buros J Gallins PJ Buxbaum JD Jarvik GP Crane PK Larson EB Bird TD Boeve BF Graff-Radford NR De Jager PL Evans D Schneider JA Carrasquillo MM Ertekin-Taner N Younkin SG Cruchaga C Kauwe JS Nowotny P Kramer P Hardy J Huentelman MJ Myers AJ Barmada MM Demirci FY Baldwin CT Green RC Rogaeva E St George-Hyslop P Arnold SE Barber R Beach T Bigio EH Bowen JD Boxer A Burke JR Cairns NJ Carlson CS Carney RM Carroll SL Chui HC Clark DG Corneveaux J Cotman CW 《Nature genetics》2011,43(5):436-441
The Alzheimer Disease Genetics Consortium (ADGC) performed a genome-wide association study of late-onset Alzheimer disease using a three-stage design consisting of a discovery stage (stage 1) and two replication stages (stages 2 and 3). Both joint analysis and meta-analysis approaches were used. We obtained genome-wide significant results at MS4A4A (rs4938933; stages 1 and 2, meta-analysis P (P(M)) = 1.7 × 10(-9), joint analysis P (P(J)) = 1.7 × 10(-9); stages 1, 2 and 3, P(M) = 8.2 × 10(-12)), CD2AP (rs9349407; stages 1, 2 and 3, P(M) = 8.6 × 10(-9)), EPHA1 (rs11767557; stages 1, 2 and 3, P(M) = 6.0 × 10(-10)) and CD33 (rs3865444; stages 1, 2 and 3, P(M) = 1.6 × 10(-9)). We also replicated previous associations at CR1 (rs6701713; P(M) = 4.6 × 10(-10), P(J) = 5.2 × 10(-11)), CLU (rs1532278; P(M) = 8.3 × 10(-8), P(J) = 1.9 × 10(-8)), BIN1 (rs7561528; P(M) = 4.0 × 10(-14), P(J) = 5.2 × 10(-14)) and PICALM (rs561655; P(M) = 7.0 × 10(-11), P(J) = 1.0 × 10(-10)), but not at EXOC3L2, to late-onset Alzheimer's disease susceptibility. 相似文献
46.
Ashley (Journal of Forecasting 1983; 2 (3): 211–223) proposes a criterion (known as Ashley's index) to judge whether the external macroeconomic variables are well forecast to serve as explanatory variables in forecasting models, which is crucial for policy makers. In this article, we try to extend Ashley's work by providing three testing procedures, including a ratio‐based test, a difference‐based test, and the Bayesian approach. The Bayesian approach has the advantage of allowing the flexibility of adapting all possible information content within a decision‐making environment such as the change of variable's definition due to the evolving system of national accounts. We demonstrate the proposed methods by applying six macroeconomic forecasts in the Survey of Professional Forecasters. Researchers or practitioners can thus formally test whether the external information is helpful. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
47.
Fertilized ova of razorback sucker, Xyrauchen texanus, were adhesive for 3 to 4 hours after fertilization. Cleavage was completed at 24 hours, gastrulation occurred at 34 hours, and blood circulation was established at 117 hours. Hatching occurred from 5.2 to 5.5 days after fertilization. Larvae were from 6.8 to 7.3 mm TL at hatching. Yolk was assimilated at 13 days (10 mm TL). All fins were formed and had ossified rays at 64 days (27 mm TL). The unique nuchal keel appeared about 200 days after fertilization. 相似文献
48.
We sampled both subspecies of the Idaho ground squirrel ( Spermophilus brunneus ) to document the larger ectoparasites of this rare endemic. S. b. brunneus was host (+ = new host record, ? = new Idaho record) to 4 flea species ( Neopsylla inopina + , Oropsylla idahoensis + , O. tuberculata , and Thrassis pandorae +), 1 tick ( Ixodes sculptus +), and an eyeworm (Nematoda: Rhabditis orbitalis ? + , also 1st records from Seiuridae); S. b. endemicus was host to a louse species ( Neohaematopinus laeviusculus +), 5 flea taxa ( Rhadinopsylla sp. + , O. t. tuberculata, Thrassis f. francisi + , T. f. barnest + , and T. f. rockwoodi ), and a mite ( Androlaelaps fahrenholzi +). Spermophilus brunneus had fewer known ectoparasite species than other congeners. Although all of their parasites had many other hosts, S. b. endemicus and S. b. brunneus shared only a single parasite species in common, whereas all but one of their ectoparasites also occurred on the closely related Townsend's ground squirrel ( S. townsendii ). The proportion of parasitized individuals and the parasite loads per individual were significantly lower in S. b. brunneus , which lives in small, isolated populations, than in S. b. endemicus , which has larger, less fragmented populations, suggesting a relationship between host population structure, parasite loads, and parasite species diversity. All but one of the flea species have been linked to plague transmission. 相似文献
49.
HIV-1 superinfection despite broad CD8+ T-cell responses containing replication of the primary virus 总被引:21,自引:0,他引:21
Altfeld M Allen TM Yu XG Johnston MN Agrawal D Korber BT Montefiori DC O'Connor DH Davis BT Lee PK Maier EL Harlow J Goulder PJ Brander C Rosenberg ES Walker BD 《Nature》2002,420(6914):434-439
Early treatment of acute HIV-1 infection followed by treatment interruptions has shown promise for enhancing immune control of infection. A subsequent loss of control, however, allows the correlates of protective immunity to be assessed. Here we show that sudden breakthrough of plasma viraemia occurred after prolonged immune containment in an individual infected with HIV-1 at a time when 25 distinct CD8+ T-cell epitopes in the viral proteins Gag, RT, Integrase, Env, Nef, Vpr, Vif and Rev were being targeted. Sequencing of the virus in plasma and cells showed that superinfection with a second clade-B virus was coincident with the loss of immune control. This sudden increase in viraemia was associated with a decline in half of the CD8+ T-cell responses. The declining CD8+ T-cell responses were coupled with sequence changes relative to the initial virus that resulted in impaired recognition. Our data show that HIV-1 superinfection can occur in the setting of a strong and broadly directed virus-specific CD8+ T-cell response. The lack of cross-protective immunity for closely related HIV-1 strains, despite persistent recognition of multiple CD8 epitopes, has important implications for public health and vaccine development. 相似文献
50.
Earl PL Americo JL Wyatt LS Eller LA Whitbeck JC Cohen GH Eisenberg RJ Hartmann CJ Jackson DL Kulesh DA Martinez MJ Miller DM Mucker EM Shamblin JD Zwiers SH Huggins JW Jahrling PB Moss B 《Nature》2004,428(6979):182-185
The potential use of smallpox as a biological weapon has led to the production and stockpiling of smallpox vaccine and the immunization of some healthcare workers. Another public health goal is the licensing of a safer vaccine that could benefit the millions of people advised not to take the current one because they or their contacts have increased susceptibility to severe vaccine side effects. As vaccines can no longer be tested for their ability to prevent smallpox, licensing will necessarily include comparative immunogenicity and protection studies in non-human primates. Here we compare the highly attenuated modified vaccinia virus Ankara (MVA) with the licensed Dryvax vaccine in a monkey model. After two doses of MVA or one dose of MVA followed by Dryvax, antibody binding and neutralizing titres and T-cell responses were equivalent or higher than those induced by Dryvax alone. After challenge with monkeypox virus, unimmunized animals developed more than 500 pustular skin lesions and became gravely ill or died, whereas vaccinated animals were healthy and asymptomatic, except for a small number of transient skin lesions in animals immunized only with MVA. 相似文献