Centric diatoms of Lake Tahoe

An understanding of the mechanisms of phytoplankton species interaction is dependent on a precise knowledge of what species exist within the community. The centric diatoms of Lake Tahoe, California-Nevada, which are often the dominant component of the phytoplankton community, are presented in both light and scanning electron microscopy (SEM) photographs. Specific attention has been given to initial cell forms of Cyclotella stelligera Cleve and Grunow and C. comta (Ehrenberg) Kützing through the aid of the SEM.     

Editorial

Systemic Practice and Action Research -     

Editorial

Systemic Practice and Action Research -     

Editorial

Systemic Practice and Action Research -     

Differential responses to nitrogen form and concentration for Oryzopsis hymenoides and Elymus lanceolatus

In a greenhouse experiment, effects of nitrogen form and concentration on productivity and dry matter allocation differed between two species native to semiarid ecosystems of the Great Basin. Aboveground production of green surface area and of dry matter were consistently enhanced by increased nitrogen for the rhizomatous grass Elymus lanceolatus , but not for the bunchgrass Oryzopsis hymenoides . These differences were likely due to inherently low growth rates of O. hymenoides . Aboveground dry matter allocation also differed between the two species. O. hymenoides had more leaves per tiller with increased nitrogen, whereas leaf size but not number increased for E. lanceolatus . Furthermore, increases in tiller density with increased nitrogen for E. lanceolatus were almost three times greater than those for O. hymenoides . E. lanceolatus , but not O. hymenoides , was sensitive to the form of nitrogen supplied to the plants. When NH 4 -N was the only form of nitrogen supplied, high concentrations of NH 4 -N inhibited aboveground production of E. lanceolatus .     

Editorial

Systemic Practice and Action Research -     

Quantitative Estimates of Outcrossing Rates in a Natural Population of Caldesia grandis （Alismataceae）

Outcrossing rate in a natural population of Caldesia grandis was estimated by the dominant random amplified polymorphism DNA (RAPD) marker using 10 open-pollinated progeny arrays of 24 individuals. The multilocus outcrossing rate estimated based on all 25 RAPD loci was 0.872 ±0.033 and the single-locus outcrossing rate was 0.795 ±0.032. Multilocus estimates did not differ significantly from the single-locus estimates. The fixation index, F, in the progeny estimated from RAPD data was -0.142 ±0.000. The estimates of multilocus outcrossing rates (t_m) and single-locus outcrossing rates (t_s) obtained from MLDT clearly indicate that outcrossing is predominant in the open-pollinated C. grandis population. An empirical analysis suggests that 15 should be the minimum number of dominant marker loci necessary to achieve robust estimates of t_m.     

Forecasting high‐frequency financial data with the ARFIMA–ARCH model

Financial data series are often described as exhibiting two non‐standard time series features. First, variance often changes over time, with alternating phases of high and low volatility. Such behaviour is well captured by ARCH models. Second, long memory may cause a slower decay of the autocorrelation function than would be implied by ARMA models. Fractionally integrated models have been offered as explanations. Recently, the ARFIMA–ARCH model class has been suggested as a way of coping with both phenomena simultaneously. For estimation we implement the bias correction of Cox and Reid ( 1987 ). For daily data on the Swiss 1‐month Euromarket interest rate during the period 1986–1989, the ARFIMA–ARCH (5,d,2/4) model with non‐integer d is selected by AIC. Model‐based out‐of‐sample forecasts for the mean are better than predictions based on conditionally homoscedastic white noise only for longer horizons (τ > 40). Regarding volatility forecasts, however, the selected ARFIMA–ARCH models dominate. Copyright © 2001 John Wiley & Sons, Ltd.