Analysis of nitrogen saturation potential in Rocky Mountain tundra and forest: implications for aquatic systems

We employed grass and forest versions of the CENTURY model under a range of N deposition values (0.02–1.60 g N m^–2 y^–1) to explore the possibility that high observed lake and stream N was due to terrestrial N saturation of alpine tundra and subalpine forest in Loch Vale Watershed, Rocky Mountain National Park, Colorado. Model results suggest that N is limiting to subalpine forest productivity, but that excess leachate from alpine tundra is sufficient to account for the current observed stream N. Tundra leachate, combined with N leached from exposed rock surfaces, produce high N loads in aquatic ecosystems above treeline in the Colorado Front Range. A combination of terrestrial leaching, large N inputs from snowmelt, high watershed gradients, rapid hydrologic flushing and lake turnover times, and possibly other nutrient limitations of aquatic organisms constrain high elevation lakes and streams from assimilating even small increases in atmospheric N. CENTURY model simulations further suggest that, while increased N deposition will worsen the situation, nitrogen saturation is an ongoing phenomenon.     

Fish species composition before and after construction of a main stem reservoir on the White River,Colorado

Synopsis The completion in the fall of 1984 of Taylor Draw Dam on the White River, Colorado, formed Kenney Reservoir — thus impounding the last significant free-flowing tributary in the Upper Colorado River Basin. Fishes were sampled above and below the dam axis prior to closure of the dam and in the reservoir and river downstream following impoundment. While immediate effects of the dam to the ichthyofauna included blockage of upstream migration to 80 km of documented range for endangered Colorado squawfish, the reservoir also proved to have profound delayed effects on the river's species composition. Pre-impoundment investigations in 1983–1984 showed strong domination by native species above, within, and below the reservoir basin. By 1989–1990, non-native species comprised roughly 90% of the fishes collected in the reservoir and 80% of the fishes collected in the river below the dam. Initially, fathead minnow, whose numbers quickly increased in the new reservoir, dominated all post-impoundment collections, but red shiner became the most abundant fish collected in the river below the dam by 1989–1990. While agency stocking programs for the reservoir sought to emphasize a sport fishery for salmonids, primarily rainbow trout, local enthusiasm for warmwater sport fishes resulted in illicit transfers of these species from nearby impoundments. Several species, formerly rare or unreported in the White River in Colorado, including white sucker, northern pike, green sunfish, bluegill, largemouth bass and black crappie, were present in the river following impoundment. Our investigation indicates smaller-scale, main-stem impoundments that do not radically alter hydrologic or thermal regimes can still have a profound influence on native ichthyofauna by facilitating establishment and proliferation of nonnative species.Cooperators are the U.S. Fish and Wildlife, the Colorado Division of Wildlife, and Colorado State University     

安徽省清凉峰自然保护区植物区系的研究

清凉峰自然保护区有维管束植物181科,601属,1228种,是安徽植物资源集中地之一。区系成分起源古老,孑遗种多,保存着丰富的珍稀、濒危植物。种子植物区系地理成分复杂,各类热带成分、温带成分、中国特有成分分别占本区种子植物属总数的33.6%、62.96%、3.44%,显示了本区植物区系的亚热带特性。本区植物区系97.6%的成分与华东植物区系共有,且含华东特有种111种,具有典型华东植物区系特征。本区植物区系与西天目山、黄山植物区系关系最密切,其次为大别山和庐山,再次为神农架。     

Impact of Atta colombica Colonies on Understory Vegetation and Light Availability in a Neotropical Forest1

We quantified patterns of vegetation removal and light availability above Atta colombica nests on Barro Colorado Island, Panama. Ants cleared vegetation less than 1 cm in diameter from an area of 77 m², and up to 3 m above ground level. Overall light availability 1.5 m above ground level was 49 percent greater at ant nest sites than at sites in undisturbed understory. These higher light levels fell within the range known to enhance growth of both shade tolerant and pioneer species.     

Use of Plant Strategy Ordination,DCA and ANOVA to elucidate relationships among habitats of Salix planifolia and Salix monticola

Abstract. Detrended Correspondence Analysis (DCA) was used on a data set of 112 species from 14 stands dominated by Salix planifolia and/or S. monticola. Environmental variables were determined which might be important to explain differences in stand vegetation composition, and willow stature (height), in willow carrs in the Rocky Mountain National Park. Correlation of environmental variables with DCA stand scores indicate that peat depth and soil redox potential are highly related to the primary DCA axis. Soils in stands of S. planifolia are more reduced in the early summer and have greater peat depths, than soils in stands of S. monticola. The second DCA axis is related to a water chemistry gradient of hydrogen ion, sulphate, and ammonium concentration. Four environmental variables selected by correlation analysis were regressed on stand scores from the first two DCA axes. Regression coefficients of August soil redox potential and soil water pH were significantly non-zero on the primary DCA axis. In addition to overall vegetation relationships elucidated by DCA, the relationships between willow stature and environmental variables were tested by simultaneous ANOVAs. ANOVA results and DCA ordinations indicate that S. planifolia and S. monticola plants achieve the greatest stature in the least reduced soils, and in shallow peat. Competitive, stress tolerant, and ruderal plant strategy theory applied to the vegetation data produced an arrangement of stands highly correlated to the DCA Axis 1 stand arrangement. These correlations indicate that the primary axis of vegetation structure can be extracted either by species composition, or species morphology/physiology relationships. Concurrent use of DCA and plant strategy theory is suggested as a tool for the prediction of community composition.     

不同起源格氏栲林分下土壤微生物生态分布的初步研究

本文研究了福建三明小湖天然起源和人工起源的格氏栲林下土壤微生物的生态分布。两种起源的格氏栲林下土壤微生物中细菌占绝对优势,人工林芽孢杆菌所占细菌总数比例远大于天然林;天然林微生物总数、细菌、真菌以及固氮菌等生理类群的数量均高于人工林,而且,随着坡位的下降表现为由低至高的递增趋势。青霉和木霉是土壤真菌的优势种属,链霉菌属中的白色类群和黄色类群构成了土壤放线菌的主要组分,但在天然林中的数量明显低于人工林。     

Optomotor reaction and fixation of walking colorado beetles (Coleoptera: Chrysomelidae): Course control aspects

The paths of Colorado beetles (Leptinotarsa decemlineata Say)in a featureless environment are circular. This behavior is explained by an internal asymmetry. To stabilize the path, the fixation reaction or the optomotor response must work against this asymmetry. The turning behavior was examined in stationary patterns of vertical stripes different at spatial wavelengths (). The internal asymmetry was tested in a horizontally striped pattern. A stable fixation reaction was found only for 120 °. The results suggest that larger intrinsic turning tendencies shifts the stable point of the fixation reaction. The same vertically striped patterns were rotated to examine the following reaction of the beetle. It is concluded that the fixation component of the response of these insects, in particular, does not differ in the two situations.     

The North American «Hipparion Datum and implications for the Neogene of the Old World

A large sample of skulls and associated dentitions of Cormohipparion sphenodus (Cope, 1889). new combination, is described from Miocene deposits of Nebraska, Colorado, New Mexico, and California. This species is morphologically more advanced than the most primitive species of the genus, C. goorisiMacFadden & Skinner, 1981, and more primitive than a third and more advanced species of this genus. C. occidentale (Leidy, 1856). In several characters such as configuration of the preobrital fossa, size, hypsodonty, shape of protocone, and complexity of enamel plication, C. sphenodus is morphologically similar, and potentially related to, some Old World Vallesian «Hipparion. In addition, based on radiometric calibration of stratigraphic sequences in Nebraska and California, C. sphenodus spans an interval of time from about 13.6 to 11 Ma. Inasmuch as the Old World «Hipparion Datum is calibrated at about 12 Ma, we conclude that C. sphenodus exhibits the morphological and chronological prerequisites to have been directly ancestral to some of these Old World forms.The hipparion horses apparently were a polyphyletic assemblage of several genera, and their biogeographic and biochronologic history is more complex than classically thought. Several dispersal events involving these horses may have occurred between the New and Old Worlds during the late Miocene.