Using Epiphytic Macrolichen Communities for Biomonitoring Ammonia in Forests of the Greater Sierra Nevada, California     

Sarah Jovan  Bruce Mccune 《Water, air, and soil pollution》2006,170(1-4):69-93

Chronic, excessive nitrogen deposition is potentially an important ecological threat to forests of the greater Sierra Nevada in California. We developed a model for ammonia bioindication, a major nitrogen pollutant in the region, using epiphytic macrolichens. We used non-metric multidimensional scaling to extract gradients in lichen community composition from surveys at 115 forested sites. A strong ammonia deposition gradient was detected, as evidenced by a high linear correlation with an index of ammonia indicator species conventionally known as “nitrophytes” (r = 0.93). This gradient, however, was confounded by elevation (r = ?0.54). We evaluated three statistical techniques for controlling the influence of elevation on nitrophytes: simple linear regression, nonlinear regression, and nonparametric regression. We used the unstandardized residuals from nonlinear regression to estimate relative ammonia deposition at each plot, primarily because this model had the best fit (r ² = 0.33), desirable asymptotic properties, and it is easy to apply to new data. Other possible sources of noise in the nitrophyte-ammonia relationship, such as substrate pH and acidic deposition, are discussed. Lichen communities indicated relatively high deposition to forests of the southern Sierra Nevada, the Modoc Plateau, as well as in stands near urban areas. Evidence of elevated ammonia was also detected for popular recreation areas such as Sequoia and Yosemite National Parks. Lichen communities from forests in the Tahoe basin, northern Sierra Nevada, southern Cascades, and eastern Klamath Range appeared considerably less impacted. This model will be used for continual assessment of eutrophication risks to forest health in the region.  相似文献   

Habitat use and spatial dynamics of takhi introduced to Hustai National Park, Mongolia     

Sarah R.B. King  John Gurnell 《Biological conservation》2005,124(2):277-290

The successful introduction of captive bred takhi or Przewalski’s horse, Equus ferus przewalskii, into Mongolia in the 1990s is a good example of the benefits of ex situ conservation and one of the few examples of the recovery of an animal after it became extinct in the wild. This is also particularly interesting because virtually nothing was known about how takhi lived before they died out, and the introductions have enabled us to study how they have settled, and their ecology and behaviour within their former natural range. In this paper, we describe the movement, home range size and shape, and habitat use of takhi at one of the release areas, the 570 km² Hustai National Park in Mongolia. Harem home ranges varied between 129 and 2399 ha, with 80% core areas of between 61 and 1196 ha. There was no relationship between range size and harem size, or length of time since release. Initially, harems stayed near their release enclosures, but over time they established home ranges further away. There was little overlap between home ranges of different harems, but neither was there evidence of exclusive range use. The more nutritious vegetation at lower elevations was preferentially selected. Thus the present situation looks good, but, as the population continues to grow, we anticipate that there will be potential problems related to intraspecific competition for water and vegetation resources, and the potential for hybridisation with domestic horses belonging to the local people. We consider the time it may take for takhi to reach carrying capacity within Hustai National Park and emphasise that continual monitoring of the population is essential because interventional management is likely to be required in the future.  相似文献   

Input-Output Budgets of Inorganic Nitrogen for 24 Forest Watersheds in the Northeastern United States: A Review     

Campbell  John L.  Hornbeck  James W.  Mitchell  Myron J.  Adams  Mary Beth  Castro  Mark S.  Driscoll  Charles T.  Kahl  Jeffrey S.  Kochenderfer  James N.  Likens  Gene E.  Lynch  James A.  Murdoch  Peter S.  Nelson  Sarah J.  Shanley  James B. 《Water, air, and soil pollution》2004,151(1-4):373-396

Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watersheds at 15 locations in the northeasternUnited States. The study watersheds are completely forested, free of recent physical disturbances, and span a geographical region bounded by West Virginia on the south and west, and Maine on the north and east. Total N budgets are not presented; however, fluxes of inorganic N in precipitation and streamwater dominate inputs and outputs of N at these watersheds. The range in inputs of DIN in wet-only precipitation from nearby National Atmospheric Deposition Program (NADP) sites was 2.7 to 8.1 kg N ha^-1 yr^-1 (mean = 6.4 kg N ha^-1 yr^-1; median = 7.0 kg N ha^-1 yr^-1). Outputs of DIN in streamwater ranged from 0.1 to 5.7 kg N ha^-1 yr^-1 (mean = 2.0 kg N ha^-1 yr^-1; median = 1.7 kg N ha^-1 yr^-1). Precipitation inputs of DIN exceeded outputs in streamwater at all watersheds, with net retention of DIN ranging from 1.2 to 7.3 kg N ha^-1 yr^-1 (mean = 4.4 kg N ha^-1 yr^-1; median = 4.6 kg N ha^-1 yr^-1). Outputs of DIN in streamwater were predominantly NO₃-N (mean = 89%; median = 94%). Wet deposition of DIN was not significantly related to DIN outputs in streamwater for these watersheds. Watershed characteristics such as hydrology, vegetation type, and land-use history affect DIN losses and may mask any relationship between inputs and outputs. Consequently, these factors need to be included in the development of indices and simulation models for predicting 'nitrogen saturation' and other ecological processes.  相似文献   

Effects of expanded mosquito range     

Bevins SN 《Science (New York, N.Y.)》2008,321(5896):1634

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Reverse leasing and power dynamics among blue agave farmers in western Mexico     

Sarah Bowen  Peter R. W. Gerritsen 《Agriculture and Human Values》2007,24(4):473-488

We examine changing production relations in the Mexican tequila industry to explore the ways in which large industrial firms are using “reverse leasing arrangements,” a form of contract farming, to extend their control over small agave farmers. Under these arrangements, smallholders rent their parcels to contracting companies who bring in capital, machinery, labor, and other agricultural inputs. Smallholders do not have access to their land, nor do they make any of the management decisions. We analyze the factors that have led some producers to participate in reverse leasing arrangements, while allowing other producers to continue farming independently. In addition, we look at the ways in which farmers are responding to these new production relations and constraints and the strategies that they are using to regain control over the production process.

Sarah BowenEmail:

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Preschool program improves cognitive control     

Diamond A  Barnett WS  Thomas J  Munro S 《Science (New York, N.Y.)》2007,318(5855):1387-1388

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Inactivation of TNF signaling by rationally designed dominant-negative TNF variants     

Steed PM  Tansey MG  Zalevsky J  Zhukovsky EA  Desjarlais JR  Szymkowski DE  Abbott C  Carmichael D  Chan C  Cherry L  Cheung P  Chirino AJ  Chung HH  Doberstein SK  Eivazi A  Filikov AV  Gao SX  Hubert RS  Hwang M  Hyun L  Kashi S  Kim A  Kim E  Kung J  Martinez SP  Muchhal US  Nguyen DH  O'Brien C  O'Keefe D  Singer K  Vafa O  Vielmetter J  Yoder SC  Dahiyat BI 《Science (New York, N.Y.)》2003,301(5641):1895-1898

Tumor necrosis factor (TNF) is a key regulator of inflammatory responses and has been implicated in many pathological conditions. We used structure-based design to engineer variant TNF proteins that rapidly form heterotrimers with native TNF to give complexes that neither bind to nor stimulate signaling through TNF receptors. Thus, TNF is inactivated by sequestration. Dominant-negative TNFs represent a possible approach to anti-inflammatory biotherapeutics, and experiments in animal models show that the strategy can attenuate TNF-mediated pathology. Similar rational design could be used to engineer inhibitors of additional TNF superfamily cytokines as well as other multimeric ligands.  相似文献   

A homolog of Drosophila grainy head is essential for epidermal integrity in mice   总被引：1，自引：0，他引：1  

Ting SB  Caddy J  Hislop N  Wilanowski T  Auden A  Zhao LL  Ellis S  Kaur P  Uchida Y  Holleran WM  Elias PM  Cunningham JM  Jane SM 《Science (New York, N.Y.)》2005,308(5720):411-413

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The chemical genomic portrait of yeast: uncovering a phenotype for all genes     

Hillenmeyer ME  Fung E  Wildenhain J  Pierce SE  Hoon S  Lee W  Proctor M  St Onge RP  Tyers M  Koller D  Altman RB  Davis RW  Nislow C  Giaever G 《Science (New York, N.Y.)》2008,320(5874):362-365

Genetics aims to understand the relation between genotype and phenotype. However, because complete deletion of most yeast genes ( approximately 80%) has no obvious phenotypic consequence in rich medium, it is difficult to study their functions. To uncover phenotypes for this nonessential fraction of the genome, we performed 1144 chemical genomic assays on the yeast whole-genome heterozygous and homozygous deletion collections and quantified the growth fitness of each deletion strain in the presence of chemical or environmental stress conditions. We found that 97% of gene deletions exhibited a measurable growth phenotype, suggesting that nearly all genes are essential for optimal growth in at least one condition.  相似文献   

Sexual selection can resolve sex-linked sexual antagonism     

Albert AY  Otto SP 《Science (New York, N.Y.)》2005,310(5745):119-121

Sexual selection is a potent evolutionary force. However, very few models have considered the evolution of female preferences for traits expressed in both sexes. Here we explore how female preferences coevolve with sexually antagonistic traits, which involve alleles that are beneficial to one sex but harmful to the other. We show that with a sexually antagonistic trait on the X chromosome (males XY, females XX), females evolve to prefer mates carrying alleles beneficial to daughters. In contrast, with a Z-linked trait (males ZZ, females ZW), females more often evolve mating preferences for mates carrying alleles beneficial to sons (that is, flashy displays).  相似文献