Stoichiometric Constraints on Food-Web Dynamics: A Whole-Lake Experiment on the Canadian Shield

A whole-lake manipulation of food-web structure (introduction of a top predator, northern pike, to a minnow-dominated lake) was performed in a Canadian Shield lake (L110) to examine the stoichiometric consequences of changes in planktonic community structure generated by altered food-web structure. Minnow abundance, zooplankton biomass and community composition, microconsumer abundance, and concentration and carbon–phosphorus (C:P) ratio of suspended particulate matter were monitored in L110 and unmanipulated L240 before (1992) and after (1993–95) pike introduction. Algal biomass in L110 determined from microscopic examination for postmanipulation and premanipulation periods was also compared with dynamics in a suite of unmanipulated reference lakes from long-term monitoring records. Pike were added in spring in 1993 and 1994 in sufficient quantity to raise pike biomass to levels of around 22 kg ha^{− 1} by 1994. Minnow populations in L110 responded dramatically, decreasing to levels 30% (1993), 10% (1994), and less than 1% (1995) of premanipulation values. However, most components lower in the food web did not respond in a manner consistent with predictions of existing food-web theory, such as the idea of cascading trophic interactions (CTI). While Daphnia biomass increased in L110 in the first year following manipulation, consistent with CTI, this effect was temporary and Daphnia collapsed in 1995, the year of lowest minnow abundance. Total zooplankton biomass in both lakes declined during the study period and, contrary to CTI, this decline appeared somewhat stronger in L110 than in L240. Dominant microconsumers (heterotrophic microflagellates) did not differ among years in either lake and did not appear to respond to food-web manipulation. At the bottom of the food web, no changes in bacterial biomass occurred in either lake. However, total concentrations of particulate matter appeared to increase in L110 after manipulation (contrary to expectations based on the theory of CTI) while algal biomass did not change in the manipulated lake relative to reference systems. Finally, particulate C:P increased in both L110 and L240 during the study period. The lack of strong response of Daphnia, the lack of response of the microbial food web, decreases in zooplankton biomass and increases in particulate biomass following reduction of minnow populations after piscivore introduction are at odds with expectations from existing food-web theory, such as the idea of CTI as currently formulated. However, the extremely high C:P ratios in particulate matter at the base of the food webs in these lakes, the coincidence of zooplankton declines and increases in particulate C:P ratios, and the results of small-scale mesocosm food-quality experiments are consistent with a hypothesis of a stoichiometric constraint operating on food-web dynamics in this and similar ecosystems. Received 22 April 1997; accepted 8 July 1997.     

An African theory of bioethics: reply to MacPherson and Macklin

In a prior issue of Developing World Bioethics, Cheryl Macpherson and Ruth Macklin critically engaged with an article of mine, where I articulated a moral theory grounded on indigenous values salient in the sub-Saharan region, and then applied it to four major issues in bioethics, comparing and contrasting its implications with those of the dominant Western moral theories, utilitarianism and Kantianism. In response to my essay, Macpherson and Macklin have posed questions about: whether philosophical justifications are something with which bioethicists ought to be concerned; why something counts as 'African'; how medicine is a moral enterprise; whether an individual right to informed consent is consistent with sub-Saharan values; and when thought experiments help to establish firm conclusions about moral status. These are important issues for the field, and I use this reply to take discussion of them a step or two farther, defending my initial article from Macpherson's and Macklin's critical questions and objections.     

正交试验优化花魔芋组织培养条件

通过正交试验优化了魔芋愈伤组织生长及出芽的条件:以花魔芋切块为外植体,在MS(或1/2MS)+6-BA1.5+NAA0.5+IBA1.0+糖30%(pH6.2)的培养基上,暗培养15～20d后,光照12h/d,不仅愈伤组织生长旺盛,而且可以一步成苗,形成完整的植株,能够按要求分批生产试管苗。     

动物实验中的兽医作用

实验动物是现代医学研究中的重要基础和条件,随着我国实验动物科学的迅速发展和实验动物和动物实验质和量的不断提高,对实验动物兽医的需求越来越大,对实验动物兽医的要求和期望也越来越高,本文简要阐述了兽医在动物实验中的作用.文章就实验动物兽医应该具备的资质、实验动物兽医的基本职责以及实验动物健康与兽医管理等方面进行了讨论,明确了实验动物兽医的各项基本职责及任务.兽医在实验动物的管理以及动物实验的过程中有着非常重要的作用,在动物实验中应充分发挥兽医的作用.     

Simultaneous estimation of levodopa and carbidopa by RP‐HPLC using a fluorescence detector: its application to a pharmaceutical dosage form

A reverse‐phase high‐performance liquid chromatographic (RP‐HPLC) method was developed and validated for the simultaneous estimation of levodopa and carbidopa in bulk and pharmaceutical formulations. Chromatographic separation was achieved by using a C₁₈ reverse‐phase column and a mixture of an aqueous phase (10 mM potassium dihydrogen phosphate buffer, pH 4.0) and methanol (90:10 v/v) as the mobile phase. Quantitative analysis of levodopa and carbidopa was performed using a fluorescence detector at an excitation wavelength of 280 nm and an emission wavelength of 310 nm. The method was linear between 5 and 500 ng/mL for both levodopa and carbidopa. The detection limits for levodopa and carbidopa were 0.30 and 0.60 ng/mL, respectively, whereas the quantitation limit was 0.80 ng/mL for levodopa and 1.2 ng/mL for carbidopa. The method demonstrated good and consistent recoveries (99.63–100.80% for levodopa and 98.97–100.94% for carbidopa) with low interday and intraday relative standard deviation. The validated method was successfully applied to quantify levodopa and carbidopa simultaneously in a pharmaceutical formulation. The method was found to be precise, sensitive and accurate for the simultaneous determination levodopa and carbidopa in bulk and pharmaceutical formulations. Copyright © 2014 John Wiley & Sons, Ltd.     

A restraining system for rhesus monkeys used in space research

A new chronic restraining system has been designed specifically for male rhesus monkeys (8–13 kg) housed in weightlessness for scientific purposes. The restraining system consists of a coat (jacket and skirt) and a chair. The system separates the thorax from the lower part of the body, and allows large movements of the upper part of the body. The macaque can feed and groom itself, and can also sleep in close-to-normal position.     

Cutting edges cut both ways

Emphasis on cutting edge science is common today. This paper shows that the concept, which selects some science at any given time as epistemically preferable and therefore better, actually gained acceptance by the turn of this century in biology and began immediately to have consequences for what biological research was done. The result, that some research is cut out while other work is privileged, can have pernicious results. Some of what is designated as not cutting edge may, in a different — and equally defensible epistemological framework, prove just as good as the officially cutting edge research. Cutting edges cut both ways, and those who study science should begin exploring the implications of that fact.     

Science and Restoration Under a Big, Demon Haunted Tent: Reply to Giardina et al. (2007)

In a recent editorial, I discussed how the culture of science, heterogeneity of nature, and real‐world human complexities can limit the practical relevance of formal scientific research and argued that less formal approaches might often be more efficient and effective. Giardina et al. criticized this editorial and argued that formal science has and increasingly will play a central role in ecological restoration in particular and human progress in general. Here, I respond to these arguments and expand upon the ideas presented in my previous editorial. I further illustrate how despite superficial appearances the utilitarian value of formal science may often be largely indirect. I also argue that the complexities of ecological and human systems combined with the subjective values and political beliefs underlying restoration make transforming this discipline into a unified “hard science” virtually impossible. Because values and politics also underlie most environmental conflicts, and scientific inquiry is inherently unsuitable for resolving these kinds of disputes, the future success of restoration may depend more on political support than scientific progress. Dogmatic, nonfalsifiable faith in the universal superiority of “rigorous” scientific knowledge and methodologies can foster arrogance and intolerance and blind us to the ephemeral nature of scientific “truths” and the double‐edged sword of scientific “progress.” My hope is that Society for Ecological Restoration International (SERI) will remain a big inclusive tent that embraces a healthy diversity of foci and approaches that emulate the extraordinary diversity we find within the natural ecosystems and human cultures we strive to preserve, restore, and reconnect.     

AFRICAN AND WESTERN MORAL THEORIES IN A BIOETHICAL CONTEXT

The field of bioethics is replete with applications of moral theories such as utilitarianism and Kantianism. For a given dilemma, even if it is not clear how one of these western philosophical principles of right (and wrong) action would resolve it, one can identify many of the considerations that each would conclude is relevant. The field is, in contrast, largely unaware of an African account of what all right (and wrong) actions have in common and of the sorts of factors that for it are germane to developing a sound response to a given bioethical problem. My aim is to help rectify this deficiency by first spelling out a moral theory grounded in the mores of many sub-Saharan peoples, and then applying it to some major bioethical issues, namely, the point of medical treatment, free and informed consent, standards of care and animal experimentation. For each of these four issues, I compare and contrast the implications of the African moral theory with utilitarianism and Kantianism, my overall purposes being to highlight respects in which the African moral theory is distinct and to demonstrate that the field should take it at least as seriously as it does the Western theories.     

Small Sample Properties of the Likelihood Estimator in Proportional Hazard Regression Models with Omitted Variables

The paper deals with the effects of incorrectly omitted regressor variables in a parametric proportional hazard regression model. By studying conditions for equality between the estimators of correct and incorrect models it is demonstrated analytically that such cases are not to be expected in practise. A small sample Monte Carlo experiment indicates severe negative effects on the retained parameters both in terms of bias and mean square error.