生物多样性分布格局的地史成因假说

生物多样性的大尺度分布格局是现代环境与地史过程共同作用的结果。本文从影响机制、参数选择及与现代气候假说的关系等方面回顾了地史成因假说的最新进展, 并得出以下认识: (1) 地史过程对生物多样性的分布格局有显著影响, 但地史过程与现代环境之间强烈的共线性使得两者的影响常叠加在一起; (2) 与广域物种的多样性相比, 地史过程更有利于解释狭域物种(或特有物种)的多样性; (3) 地史过程的参数选择是地史假说所面临的挑战之一, 目前所用的指标与现代环境具有显著的共线性, 难以直观地体现地史过程对生物多样性的影响, 对不同区域内物种系统发育过程的对比或者物种形成速率及灭绝速率分布格局的分析可能有助于评价地史成因假说的影响。     

Respiration rate of arctic plants as related to the production process

This work deals with two intertwined questions: (1) what are the factors underlying equally high respiration rates of arctic plants at low temperature and of temperate zone plants at 20–25°C and (2) whether this respiration feature would explain small size of the northern plants. In an attempt to answer these questions, we collected various hypotheses scattered in the current literature and experimentally examined the respiration- growth relationships by analyzing plant productivity characteristics in three representative species inhabiting Wrangel Island (lat. 71°N). The results show that the components of the production process stay in accord in the arctic plants so that their productivity characteristics at low temperatures are nearly the same as in the temperate zone plants at higher temperatures. Hence, respiration cannot account for small size of the northern plants. Upon the experimental results and general concepts for regulation of respiration, we conclude that the intense respiration of plants inhabiting cold climate regions is caused by higher metabolic demands for energy and intermediates under the northern conditions. The enhanced metabolic demands of plants at low temperature represent the main factor of intense respiration.     

Native Cuscuta campestris restrains exotic Mikania micrantha and enhances soil resources beneficial to natives in the invaded communities

Nutrients in exotic species and invaded communities play a key role in determining the dynamics of invaders and the invasibility of a receipt community. This study focused on the effects of the native holoparasite Cuscuta campestris (for short Cuscuta) on nutrients in the exotic invasive Mikania micrantha (for short Mikania) and stands invaded by Mikania. We conducted a set of field investigations on Mikania with Cuscuta parasitism for 1–4 years, and measured soil properties, community composition, and the growth and nutrient content of Mikania and Cuscuta in two types of sub-communities (i.e. with Mikania only, or with Mikania and Cuscuta). Cuscuta dramatically reduced the cover, biomass, and nutrients (i.e. N, P, and K content) of Mikania, significantly enhanced soil water, pH and nutrient content (i.e. organic matter, total N and P, available P and K), and greatly increased the cover and species richness of native plants. In addition, N and K of Cuscuta were positively correlated with N of Mikania, which was negatively associated with soil total N, available P and K. These findings suggest that Cuscuta may be an effective measure against Mikania and be beneficial to the restoration of invaded communities.     

Weeds and biodiversity conservation: A review of managing weeds under the New South Wales Threatened Species Conservation Act 1995

Summary   In New South Wales, alien plants pose the second greatest threat to biodiversity behind land clearing and habitat loss, yet current weed management does not always address the biodiversity at risk or put in place mechanisms to ensure their recovery. The problem arises in part from an assumption that control programmes which focus only on the weed will result in a biodiversity benefit, rather than acknowledging the need for an assessment of the biodiversity at risk and subsequent incorporation of such information into management strategies. The New South Wales Threatened Species Conservation Act 1995 (TSC Act) has been used as a tool to integrate weed control and biodiversity management through the listing of weeds as key threatening processes and the development and implementation of Threat Abatement Plans (TAPs). Through this process, weed management is forced to focus on actual biodiversity conservation outcomes by directing control to areas where the likelihood of a positive biodiversity response is maximized. Bitou Bush ( Chrysanthemoides monilifera ssp. rotundata ) was the first weed species listed under the TSC Act as a key threatening process and to have a TAP prepared. Implementation of the Bitou Bush TAP is now potentially assisting the recovery of over 150 native plant species and 24 ecological communities at more than 160 sites. The TAP process is now being used for Lantana ( Lantana camara ) nationally and for all widespread weed species that threaten biodiversity within each of the 13 Catchment Management Authorities across New South Wales. By focusing the objectives of weed control on biodiversity protection and recovery, and ensuring that sites throughout the distribution of the weed are prioritized, threat reduction and conservation outcomes are more likely to occur at a landscape scale.     

Hierarchical models facilitate spatial analysis of large data sets: a case study on invasive plant species in the northeastern United States

Many critical ecological issues require the analysis of large spatial point data sets – for example, modelling species distributions, abundance and spread from survey data. But modelling spatial relationships, especially in large point data sets, presents major computational challenges. We use a novel Bayesian hierarchical statistical approach, 'spatial predictive process' modelling, to predict the distribution of a major invasive plant species, Celastrus orbiculatus , in the northeastern USA. The model runs orders of magnitude faster than traditional geostatistical models on a large data set of c . 4000 points, and performs better than generalized linear models, generalized additive models and geographically weighted regression in cross-validation. We also use this approach to model simultaneously the distributions of a set of four major invasive species in a spatially explicit multivariate model. This multispecies analysis demonstrates that some pairs of species exhibit negative residual spatial covariation, suggesting potential competitive interaction or divergent responses to unmeasured factors.     

浅谈间歇式活性污泥法

为了防止水体污染的加重,水处理技术得到了深入研究和迅速发展,从而促进了水质净化新工艺的不断出现和广泛应用。间歇式活性污泥法工艺能满足排放要求、处理效果好、运行费用低,作为一种污水处理新技术、新工艺发展迅速。本文从SBR工艺的基本原理出发,介绍了几种SBR的改良工艺,并突出其工艺特征。     

Evolutionary dynamics of tumor progression with random fitness values

Most human tumors result from the accumulation of multiple genetic and epigenetic alterations in a single cell. Mutations that confer a fitness advantage to the cell are known as driver mutations and are causally related to tumorigenesis. Other mutations, however, do not change the phenotype of the cell or even decrease cellular fitness. While much experimental effort is being devoted to the identification of the functional effects of individual mutations, mathematical modeling of tumor progression generally considers constant fitness increments as mutations are accumulated. In this paper we study a mathematical model of tumor progression with random fitness increments. We analyze a multi-type branching process in which cells accumulate mutations whose fitness effects are chosen from a distribution. We determine the effect of the fitness distribution on the growth kinetics of the tumor. This work contributes to a quantitative understanding of the accumulation of mutations leading to cancer.     

Direct interaction between Utp8p and Utp9p contributes to rRNA processing in budding yeast

The small subunit (SSU) processome is an evolutionarily conserved ribonucleoprotein (RNP) complex that consists of U3 snoRNA and at least 40 protein components. The SSU processome is required for the generation of 18S rRNA in the budding yeast Saccharomyces cerevisiae. In this study we demonstrate that two essential components of the SSU processome, Utp8p and Utp9p, must interact directly for the SSU processome to function properly. Disruption of the Utp8p-Utp9p interaction by mutation of the respective interacting domain led to a compromised ability of yeast cells to process 35S pre-rRNA into 18S pre-rRNA. Loss of the Utp8p-Utp9p interaction also led to a decrease in the amount of Utp8p that interacted with U3 small nucleolar RNAs (snoRNAs) but did not affect the amount of Utp9p bound to U3 snoRNA, suggesting that Utp8p associates with the SSU processome by virtue of its interaction with Utp9p. Together, our data support a model where Utp8p and Utp9p must interact directly and functionally in the U3-containing SSU processome for optimal rRNA biosynthesis to occur in budding yeast.     

Bayesian Semiparametric Multiple Shrinkage

Summary High‐dimensional and highly correlated data leading to non‐ or weakly identified effects are commonplace. Maximum likelihood will typically fail in such situations and a variety of shrinkage methods have been proposed. Standard techniques, such as ridge regression or the lasso, shrink estimates toward zero, with some approaches allowing coefficients to be selected out of the model by achieving a value of zero. When substantive information is available, estimates can be shrunk to nonnull values; however, such information may not be available. We propose a Bayesian semiparametric approach that allows shrinkage to multiple locations. Coefficients are given a mixture of heavy‐tailed double exponential priors, with location and scale parameters assigned Dirichlet process hyperpriors to allow groups of coefficients to be shrunk toward the same, possibly nonzero, mean. Our approach favors sparse, but flexible, structure by shrinking toward a small number of random locations. The methods are illustrated using a study of genetic polymorphisms and Parkinson's disease.     

Semiparametric Bayesian Analysis of Nutritional Epidemiology Data in the Presence of Measurement Error

Summary : We propose a semiparametric Bayesian method for handling measurement error in nutritional epidemiological data. Our goal is to estimate nonparametrically the form of association between a disease and exposure variable while the true values of the exposure are never observed. Motivated by nutritional epidemiological data, we consider the setting where a surrogate covariate is recorded in the primary data, and a calibration data set contains information on the surrogate variable and repeated measurements of an unbiased instrumental variable of the true exposure. We develop a flexible Bayesian method where not only is the relationship between the disease and exposure variable treated semiparametrically, but also the relationship between the surrogate and the true exposure is modeled semiparametrically. The two nonparametric functions are modeled simultaneously via B‐splines. In addition, we model the distribution of the exposure variable as a Dirichlet process mixture of normal distributions, thus making its modeling essentially nonparametric and placing this work into the context of functional measurement error modeling. We apply our method to the NIH‐AARP Diet and Health Study and examine its performance in a simulation study.