Niche partitioning among Prochlorococcus ecotypes along ocean-scale environmental gradients     

Johnson ZI  Zinser ER  Coe A  McNulty NP  Woodward EM  Chisholm SW 《Science (New York, N.Y.)》2006,311(5768):1737-1740

Prochlorococcus is the numerically dominant phytoplankter in the oligotrophic oceans, accounting for up to half of the photosynthetic biomass and production in some regions. Here, we describe how the abundance of six known ecotypes, which have small subunit ribosomal RNA sequences that differ by less than 3%, changed along local and basin-wide environmental gradients in the Atlantic Ocean. Temperature was significantly correlated with shifts in ecotype abundance, and laboratory experiments confirmed different temperature optima and tolerance ranges for cultured strains. Light, nutrients, and competitor abundances also appeared to play a role in shaping different distributions.  相似文献   

Plant genotypic diversity predicts community structure and governs an ecosystem process   总被引：1，自引：0，他引：1  

Crutsinger GM  Collins MD  Fordyce JA  Gompert Z  Nice CC  Sanders NJ 《Science (New York, N.Y.)》2006,313(5789):966-968

Theory predicts, and recent empirical studies have shown, that the diversity of plant species determines the diversity of associated herbivores and mediates ecosystem processes, such as aboveground net primary productivity (ANPP). However, an often-overlooked component of plant diversity, namely population genotypic diversity, may also have wide-ranging effects on community structure and ecosystem processes. We showed experimentally that increasing population genotypic diversity in a dominant old-field plant species, Solidago altissima, determined arthropod diversity and community structure and increased ANPP. The effects of genotypic diversity on arthropod diversity and ANPP were comparable to the effects of plant species diversity measured in other studies.  相似文献   

Public health. Getting HIV treatment to the most people     

S Lynch  N Ford  G van Cutsem  H Bygrave  B Janssens  T Decroo  I Andrieux-Meyer  T Roberts  S Balkan  E Casas  C Ferreyra  M Bemelmans  J Cohn  P Kahn  E Goemaere 《Science (New York, N.Y.)》2012,337(6092):298-300

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Mechanical Testing of Orthopedic Suture Material Used for Extra‐Articular Stabilization of Canine Cruciate Ligament‐Deficient Stifles     

Nathan D. Rose DVM  Derek Goerke  Richard B. Evans PhD  Michael G. Conzemius DVM  PhD  Diplomate ACVS 《Veterinary surgery : VS》2012,41(2):266-272

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Hematologic and IgG responses of heifers experimentally infected with the agent of epizootic bovine abortion     

Coker MR  Rauw WM  Nieto NC  Thain D  Teglas MB 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2012,41(3):344-352

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Sulfometuron methyl influences seedling growth and leaf function of three conifer species   总被引：1，自引：0，他引：1  

Nathan D. Robertson  Anthony S. Davis 《New Forests》2012,43(2):185-195

Seedling growth and gas exchange responses were measured for two potted seedling trials testing herbicide phytotoxicity to three important tree species of the Inland Northwest, USA. Media-filled pots were treated with sulfometuron methyl (Oust^?) in varying concentrations and planted with seedlings of Larix occidentalis Nutt., Pseudotsuga menziesii var. glauca (Beissn.) Franco, and Pinus monticola Dougl. ex D. Don. Seedlings were grown in two trials to determine the effects of two important residue breakdown factors, substrate moisture and pH, relative to that of herbicide application rate on seedling health. Changes in seedling height, root-collar diameter, and root volume were morphologic variables of interest, and physiological variables measured were net photosynthetic assimilation, stomatal conductance, and transpiration rate. While three levels of media moisture and four levels of media pH had no effect on seedling performance, most growth and leaf function variables were hindered across application rate treatments of all three species. Label-recommended dosages resulted in growth suppression levels potentially detrimental to seedling establishment for all three species. This was most pronounced for Pinus monticola, in particular for root growth, where untreated control seedlings showed 109% more root volume growth than treated seedlings. We conclude that when possible, a species-specific application rate might be found that balances the benefits of vegetation control with the phytotoxicity to promote optimal growth gains.  相似文献   

Timing of breeding in <Emphasis Type="Italic">Ochrotomys nuttalli</Emphasis> and <Emphasis Type="Italic">Peromyscus leucopus</Emphasis> is related to a latitudinal isotherm     

Nathan L. Pratt  Gary W. Barrett 《Landscape Ecology》2012,27(4):599-610

Previous comparative studies on patterns of reproduction in small-mammal species focus primarily on latitudinal differences in average litter size. Few studies compare reproductive patterns among northern and southern populations at the landscape scale. Our study compares differences in seasonal patterns of reproduction in northern and southern populations of the golden mouse, Ochrotomys nuttalli, and the white-footed mouse, Peromyscus leucopus. These are remarkably similar species with regard to bioenergetics, body mass, feeding behavior, home-range size, natural history, nest-site preference, and periods of activity. Both species also exhibit very similar intraspecific seasonal patterns of reproduction across their respective geographic ranges. We found that O. nuttalli and P. leucopus switch from a summer breeding season, extending from late spring through early autumn in the north to a winter breeding season extending from late autumn through early spring in the south, near the isotherm where mean annual temperature is 15.6°C (60°F), or approximately 35° N latitude. This latitudinal isotherm provides a geographic benchmark to address future changes in patterns of reproduction attributed to climate change. Findings also suggest that length of the breeding season and patterns of reproduction between species partially explain why P. leucopus is typically more abundant than O. nuttalli in similar habitat types.  相似文献   

Relationships among subgross anatomy, computed tomography, and histologic findings in dogs with disease localized to the pulmonary acini     

Scrivani PV  Thompson MS  Dykes NL  Holmes NL  Southard TL  Gerdin JA  Bezuidenhout AJ 《Veterinary radiology & ultrasound》2012,53(1):1-10

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Mapping Total Vegetation Cover Across Western Rangelands With Moderate-Resolution Imaging Spectroradiometer Data     

Stephen C. Hagen  Philip Heilman  Robert Marsett  Nathan Torbick  William Salas  Jenni van Ravensway  Jiaguo Qi 《Strength and Conditioning Journal》2012,65(5):456-467

Remotely sensed observations of rangelands provide a synoptic view of vegetation condition unavailable from other means. Multiple satellite platforms in operation today (e.g. Landsat, moderate-resolution imaging spectroradiometer [MODIS]) offer opportunities for regional monitoring of rangelands. However, the spatial and temporal variability of rangelands pose challenges to consistent and accurate mapping of vegetation condition. For instance, soil properties can have a large impact on the reflectance registered at the satellite sensor. Additionally, senescent vegetation, which is often abundant on rangeland, is dynamic and its physical and photochemical properties can change rapidly along with moisture availability. Remote sensing has been successfully used to map local rangeland conditions. However, regional and frequently updated maps of vegetation cover in rangelands are not currently available. In this research, we compare ground measurements of total vegetation cover, including both green and senescent cover, to reflectance observed by the satellite and develop a robust method for estimating total vegetation canopy cover over diverse regions of the western United States. We test the effects of scaling from ground observations up to the Landsat 30-m scale, then to the MODIS 500-m scale, and quantify sources of noise. The soil-adjusted total vegetation index (SATVI) captures 55% of the variability in ground measured total vegetation cover from diverse sites in New Mexico, Arizona, Wyoming, and Nevada. Scaling from the Landsat to MODIS scale introduces noise and loss of spatial detail, but offers inexpensive and frequent observations and the ability to track trends in cover over large regions.  相似文献   

Prey and non‐native fish predict the distribution of Colorado pikeminnow (Ptychocheilus lucius) in a south‐western river in North America     

Nathan R. Franssen  Scott L. Durst 《Ecology of Freshwater Fish》2014,23(3):395-404

Colorado pikeminnow (Ptychocheilus lucius) has been extirpated from a large portion of its historical range in the Colorado River basin, USA. A repatriation effort via stocking of juvenile P. lucius in the San Juan River, NM, CO and UT has resulted in limited recruitment of individuals into an adult population. Understanding biotic and abiotic factors that limit their persistence in the Colorado River basin will be a critical step in providing for their recovery. To elucidate potential recruitment barriers in the San Juan River, we assessed relationships between the numbers of two age classes of P. lucius and prey, competitors and predators collected at a 1.6 km reach scale between 2003 and 2012. We used an information theoretical approach to rank candidate models testing the relative importance of these biotic conditions in predicting the spatial distribution of P. lucius. We found positive relationships between the numbers of P. lucius ≤200 mm total length (TL) collected and catch per unit effort (CPUE) of native prey among reaches. For P. lucius >200 mm TL (individuals that are likely completely piscivorous), we found positive associations between the numbers of P. lucius collected and CPUE of total prey and CPUE of potential non‐native competitors in each reach. Our data suggest size‐specific affinities of P. lucius for native and non‐native prey as well as the potential for negative interactions between P. lucius and non‐native competitors may contribute to limited recruitment of juvenile P. lucius into an adult population in the San Juan River.  相似文献