结构稳定性: 概念、方法和应用

群落内物种间相互作用的结构是高度组织化的。群落结构对多物种共存的影响机制是群落生态学的核心科学问题之一。目前生态学界在这一问题上存在多种不同的观点。一个可能的原因是, 由于环境因子的复杂性, 大部分研究忽略了环境因子对群落结构和物种共存的重要影响。在这一背景下, 近期发展起来的结构稳定性理论系统地联系了群落结构、环境因子和物种共存, 并在此基础上建立了一个和经验数据紧密结合的理论框架。本文首先简要回顾了当前关于群落结构研究的争鸣, 然后介绍了结构稳定性的理论框架和计算方法, 最后详细介绍了结构稳定性理论在不同生态群落和不同生态学问题中的应用。在全球气候变化的背景下, 结构稳定性理论提供了一种新的视角来理解群落层面的生物多样性维持机制。     

The Play is Now Reality: Affective Turns, Narrative Struggles, and Theorizing Emotion as Practical Experience

Discursive approaches to subjectivity have been critiqued most recently for its dismissal of a living body that moves and senses. While identity as performative has proven invaluable to contemporary cultural theory for its dynamic conceptualization of power in everyday practice, the emergence of what some scholars have named an “affective turn” has prompted calls for configuring the body as more than a complex set of significations, but also a vibrant energy field in perpetual emergence. Centered on an enacted story created by two clinical therapists and two South Asian immigrant domestic violence survivors during a therapeutic support group session, this paper brings the affective turn into dialog with narrative theory. I juxtapose two different readings of this clinical “performance.” One interpretation recognizes affect theory’s value for highlighting sensation and the virtual in moments of transformation. Nonetheless I argue it overlooks a lived history. Thus, using a specifically dramatistic approach to narrative, the second analysis stresses the importance of personal experience and meaning-making in strengthening the link between affect and subjectivity. In doing so, the case study also argues for emotion’s critical link to practical and moral experience.     

Genetic variation, predator-prey interactions and food web structure

Food webs are networks of species that feed on each other. The role that within-population phenotypic and genetic variation plays in food web structure is largely unknown. Here, I show via simulation how variation in two key traits, growth rates and phenology, by influencing the variability of body sizes present through time, can potentially affect several structural parameters in the direction of enhancing food web persistence: increased connectance, decreased interaction strengths, increased variation among interaction strengths and increased degree of omnivory. I discuss other relevant traits whose variation could affect the structure of food webs, such as morphological and additional life-history traits, as well as animal personalities. Furthermore, trait variation could also contribute to the stability of food web modules through metacommunity dynamics. I propose future research to help establish a link between within-population variation and food web structure. If appropriately established, such a link could have important consequences for biological conservation, as it would imply that preserving (functional) genetic variation within populations could ensure the preservation of entire communities.     

Night,sight, and feeling safe: An exploration of aspects of Warlpiri and Western sleep

Sleeping leaves those asleep ‘blind’ and hence oblivious to potential or real danger. Such dangers are heightened further and more feared at night, the main time for sleep. In this article, I link ideas about sleep and nighttime social practices with questions about vision. My aim is to tease out some of the meanings implied in cross‐culturally distinct solutions to the protection of sleepers at night. I proceed by contrasting ethnographic data from the remote Aboriginal settlement of Yuendumu, Northern Territory, with select elements of the cultural history of Euro‐American sleep. Through ethnographic vignettes, I illuminate how people at Yuendumu commonly arrange themselves in yunta, or rows of sleepers, at night, and how some sleepers awake regularly during the night to ensure the others’ safety. I contrast this with Euro‐American ways of providing a sense of safety to the sleeper through practices of domestic fortification. My comparison revolves around the notion of sight, which in the Euro‐American West is clearly linked to ideas of knowledge, and at Yuendumu, as I demonstrate, imbued with a sense of care. I conclude by relating the gained insights to participant observation as anthropological method.     

Linking individual diet variation and fecundity in an omnivorous marine consumer

Individual diet variation is a common feature of populations. This variation may be particularly common in near-shore marine benthic habitats where omnivory is prevalent and prey availability is spatially variable. Accurately predicting population responses to anthropogenic change that is occurring rapidly in these systems requires a quantitative link between individual diet variation and fecundity. Here I develop this quantitative link for the European green crab Carcinus maenas, specifically focusing on variation in the relative amounts of plant and animal material included in the diet. I demonstrate both short- and long-term diet variation between crabs as well as large individual variation in fecundity. I then quantitatively link variation in diet and fecundity using a laboratory feeding experiment. Fecundity increased by approximately 5,200 eggs when daily consumption of animal tissue increased by 1 % of body weight, but was not influenced by the most commonly consumed algal species. Results presented here have important implications for understanding population dynamics in general, and also provide information necessary for accurately predicting population growth of this widespread invader.     

The endocytic machinery at an interface with the actin cytoskeleton: a dynamic,hip intersection

Clathrin-mediated endocytosis is the major mechanism by which proteins and membrane lipids gain access into cells. Over the past several years, an array of proteins has been identified that define the molecular machinery regulating the formation of clathrin-coated pits and vesicles. This article focuses on how the identification of this machinery has begun to reveal a molecular basis for a link between endocytosis and the actin cytoskeleton--a link that had long been suspected to exist in mammalian cells but which had remained elusive. In particular, I discuss the relationship between actin and three components of the endocytic machinery--dynamin, HIPs (huntingtin-interacting proteins) and intersectin.     

Event train decoders with many inputs,pulse density versus momentaneous frequency

An analysis is made of the transformations a graded signal undergoes if it is first encoded as a train of identical impulses, and subsequently decoded into a graded signal again. The case treated is that of a sinusoidally modulated input signal. As a paradigm for the encoding stage we employ the I.P.F.M. (Integral Pulse Frequency Modulator). An exact solution for the times of occurrence of output impulses is offered. This solution permits us to treat some curious beat phenomena that are found if an I.P.F.M. is excited with a frequency that is in a nearly rational ratio to the steady state output frequency of the I.P.F.M. It is shown that an I.P.F.M. is a phase sensitive device. In order to avoid a phase sensitivity of the complete signal transmission link, we consider a group of encoders feeding their signals into the decoding stage. For such a group it is meaningful to talk about the momentaneous interpulse interval. We derive the interval histogram and the spectral decomposition of this momentaneous interval. It is shown that the spectrum is very different from the spectrum derived by Bayly (1968) of the output signal of a single I.P.F.M. Two extreme types of decoding mechanisms lead to different transfer functions for the complete signal transmission link, both of which are shown to be of some neurophysiological relevance.     

Synapsin I, a neuron-specific phosphoprotein interacting with small synaptic vesicles and F-actin

Synapsin I is a neuron-specific phosphoprotein which is a substrate for cAMP- and Ca2+/calmodulin-dependent protein kinases. It is specifically localized to the cytoplasmic side of small synaptic vesicles. The interaction of synapsin I with the synaptic vesicle membrane is complex in nature, since it is modulated by phosphorylation and involves binding of different domains of the molecule to phospholipid and protein components of synaptic vesicles. Synapsin I is also able to interact with actin filaments in a phosphorylation-dependent manner. Because of these properties, it has been hypothesized that synapsin I acts as a dynamic link between synaptic vesicles an the actin meshwork of the nerve terminal, thereby modulating the release of neurotransmitter.     

Error management,reliability and cognitive evolution

The paper offers a partial vindication of Sterelny’s view on the role of error rates and reliability in his theory of decoupled representation based on modelling techniques borrowed from the biological literature on evolution in stochastic environments. In the case of a tight link between tracking states and behaviour, I argue that in its full generality Sterelny’s account instantiates the base-rate fallacy. With regard to non-tightly linked behaviour, I show that Sterelny’s account can be vindicated subject to an adequate evolutionary model and a suitable notion of reliability.     

mTOR coordinates protein synthesis,mitochondrial activity and proliferation

Protein synthesis is one of the most energy consuming processes in the cell. The mammalian/mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that integrates a multitude of extracellular signals and intracellular cues to drive growth and proliferation. mTOR activity is altered in numerous pathological conditions, including metabolic syndrome and cancer. In addition to its well-established role in regulating mRNA translation, emerging studies indicate that mTOR modulates mitochondrial functions. In mammals, mTOR coordinates energy consumption by the mRNA translation machinery and mitochondrial energy production by stimulating synthesis of nucleus-encoded mitochondria-related proteins including TFAM, mitochondrial ribosomal proteins and components of complexes I and V. In this review, we highlight findings that link mTOR, mRNA translation and mitochondrial functions.     

mTOR coordinates protein synthesis,mitochondrial activity and proliferation

Protein synthesis is one of the most energy consuming processes in the cell. The mammalian/mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that integrates a multitude of extracellular signals and intracellular cues to drive growth and proliferation. mTOR activity is altered in numerous pathological conditions, including metabolic syndrome and cancer. In addition to its well-established role in regulating mRNA translation, emerging studies indicate that mTOR modulates mitochondrial functions. In mammals, mTOR coordinates energy consumption by the mRNA translation machinery and mitochondrial energy production by stimulating synthesis of nucleus-encoded mitochondria-related proteins including TFAM, mitochondrial ribosomal proteins and components of complexes I and V. In this review, we highlight findings that link mTOR, mRNA translation and mitochondrial functions.     

Dynamin I phosphorylation and the control of synaptic vesicle endocytosis

The GTPase dynamin I is essential for synaptic vesicle endocytosis in nerve terminals. It is a nerve terminal phosphoprotein that is dephosphorylated on nerve terminal stimulation by the calcium-dependent protein phosphatase calcineurin and then rephosphorylated by cyclin-dependent kinase 5 on termination of the stimulus. Because of its unusual phosphorylation profile, the phosphorylation status of dynamin I was assumed to be inexorably linked to synaptic vesicle endocytosis; however, direct proof of this link has been elusive until very recently. This review will describe current knowledge regarding dynamin I phosphorylation in nerve terminals and how this regulates its biological function with respect to synaptic vesicle endocytosis.     

Policies and public opinion towards immigrants: the Spanish case

By tackling negative opinions towards immigration we can create a basis to orientate policies that seek to reduce them. My purpose is to highlight that the analysis of immigration in Spain exemplifies a clear link between policies and public opinion. It is this link that is at the basis of what I will call the ambivalence of Spanish public opinion, when border and integration issues are compared.     

Influence of the unusual covalent adduct on the kinetics and formation of radical intermediates in synechocystis catalase peroxidase: a stopped-flow and EPR characterization of the MET275, TYR249, and ARG439 variants

Catalase-peroxidases (KatGs) are heme peroxidases with a catalatic activity comparable to monofunctional catalases. They contain an unusual covalent distal side adduct with the side chains of Trp(122), Tyr(249), and Met(275) (Synechocysis KatG numbering). The known crystal structures suggest that Tyr(249) and Met(275) could be within hydrogen-bonding distance to Arg(439). To investigate the role of this peculiar adduct, the variants Y249F, M275I, R439A, and R439N were investigated by electronic absorption, steady-state and transient-state kinetic techniques and EPR spectroscopy combined with deuterium labeling. Exchange of these conserved residues exhibited dramatic consequences on the bifunctional activity of this peroxidase. The turnover numbers of catalase activity of M275I, Y249F, R439A, and R439N are 0.6, 0.17, 4.9, and 3.14% of wild-type activity, respectively. By contrast, the peroxidase activity was unaffected or even enhanced, in particular for the M275I variant. As shown by mass spectrometry and EPR spectra, the KatG typical adduct is intact in both Arg(439) variants, as is the case of the wild-type enzyme, whereas in the M275I variant the covalent link exists only between Tyr(249) and Trp(122). In the Y249F variant, the link is absent. EPR studies showed that the radical species formed upon reaction of the Y249F and R439A/N variants with peroxoacetic acid are the oxoferryl-porphyrin radical, the tryptophanyl and the tyrosyl radicals, as in the wild-type enzyme. The dramatic loss in catalase activity of the Y249F variant allowed the comparison of the radical species formed with hydrogen peroxide and peroxoacetic acid. The EPR data strongly suggest that the sequence of intermediates formed in the absence of a one electron donor substrate, is por(.-)(+) --> Trp(.-) (or Trp(.-)(+)) --> Tyr(.-). The M275I variant did not form the Trp(.-) species because of the dramatic changes on the heme distal side, most probably induced by the repositioning of the remaining Trp(122)-Tyr(249) adduct. The results are discussed with respect to the bifunctional activity of catalase-peroxidases.     

"Sweeping up after the parade": professional, ethical, and patient care implications of "turfing"

"Turfing" denotes a patient transfer or triage from one physician to another when the care of that patient feels more troublesome than it is worth. A widespread phenomenon in medical training programs, turfing appears to allocate patient care to meet physicians' rather than patients' needs. Although turfing reportedly causes inter-physician discord and inter-specialty stereotyping, its deeper consequences are poorly understood. Turfing is an interpersonal conflict masquerading as a medical issue. After examining turfing alongside other patient-related slang, I analyze the distinction between "the turf," a person, and "to turf," a practice. Several explanatory models from medical practice are explored in order to illuminate turfing's implications for medical professionalism, ethics, and patient care. I suggest that a physician's medical specialty or practice type--that is, professional culture--may link to that physician's degree of altruism. If so, then what it means fundamentally to be a physician might vary across medical specialties. Such a link calls for a new notion of cultural competence, one that physicians may apply not to patients but to each other.     

Caring Through Restraint: Violence,Intimacy and Identity in Mental Health Practice

In this article, I discuss the meanings of “restraints,” or physical intervention strategies that are used at a total institution for mentally ill adolescents in the United States. This paper argues that this particularly complex form of mental health treatment is simultaneously a violent and an intimate way in which men relate to one another and also takes on complex meanings about trust and identity in mental health recovery. Using data from 18 months of ethnographic fieldwork at one residential treatment center, this article examines what restraints reveal and embody about intimate interpersonal staff/client relationships, how Black men relate to one another in this setting and how staff members use physical interventions to link institutional mental health treatment with street violence in the outside world. I conclude that understanding these meanings of restraints provides a valuable way of understanding local knowledge in mental health practice, treatment and recovery.     

A virtual hair cell, II: evaluation of mechanoelectric transduction parameters

The virtual hair cell we have proposed utilizes a set of parameters related to its mechanoelectric transduction. In this work, we observed the effect of such channel gating parameters as the gating threshold, critical tension, resting tension, and Ca(2+) concentration. The gating threshold is the difference between the resting and channel opening tension exerted by the tip link assembly on the channel. The critical tension is the tension in the tip link assembly over which the channel cannot close despite Ca(2+) binding. Our results show that 1), the gating threshold dominated the initial sensitivity of the hair cell; 2), the critical tension minimally affects the peak response, (I), but considerably affects the time course of response, I(t), and the force-displacement, F-X, relationship; and 3), higher intracellular [Ca(2+)] resulted in a smaller fast adaptation time constant. Based on the simulation results we suggest a role of the resting tension: to help overcome the viscous drag of the hair bundle during the oscillatory movement of the bundle. Also we observed the three-dimensional bundle effect on the hair cell response by varying the number of cilia forced. These varying forcing conditions affected the hair cell response.     

Fasu Solidarity: A Case Study of Kin Networks, Land Tenure, and Oil Extraction in Kutubu, Papua New Guinea

In the Fasu region of Papua New Guinea's fringe highlands, the oil extraction industry has imposed development values and the identification of corporate groups as beneficiary landowners. In response, Fasu males have tightened the boundaries of their agnatic descent groups to become exclusive patriunits. Cash royalties are incorporated into sociopolitical exchange, so the formation of exclusive kin groups allows males to expand social networks to other regions, whilst ensuring continuing wealth for future generations. Consequently, males are becoming isolated from pre–oil exchange networks, and females are becoming isolated within villages. In this article, I map the transition of Fasu kin networks from an ideology of descent to a dogma of descent and patrilineal solidarity, locating the transition in the symbolic codes that inform kin categories. I aim to highlight some consequences of "development" and to advance knowledge on the link between kinship and descent in a postcolonial, industry-dominated Papua New Guinea.     

Differences in I band structure,sarcomere extensibility,and electrophoresis of titin between two muscle fiber types of the perch (Perca fluviatilis L.)

I bands of perch muscle contain crosslinks that interconnect the thin filaments as well as the connecting filaments and link them to the membrane systems and to other intermyofibrillar material. In shortened sarcomeres cross connections seem to pile up in the I band and at the A/I band junction. Sarcomeres of red fibers, which in another study are reported to have steep passive stress-strain curves, were pulled apart when they were stretched by about 40% of their slack length. Sarcomeres of white fibers could be stretched by almost 100% and still display filament alignment. Sarcomeres of the red fibers also differed from those of white fibers in the distance over which connecting filaments could be discerned, the presence of an extra transverse filament in their NI lines, the electrophoretic mobility of titin, and the titin/actin ratio.     

Systemic hypertension, headache, and ocular hemodynamics: a new hypothesis

The association between systemic hypertension and headache remains controversial and its pathophysiologic basis is uncertain. A rather characteristic early-morning pulsating headache is commonly seen in hypertensive patients, and a recent meta-analysis supports the link between these 2 entities. Epidemiologic evidence has paradoxically suggested a negative association between hypertension and headache. Unpredictable clinical association between severe hypertension and headache indicates that another cranial perfusion-related variable exerts a critical role. Neuroanatomically, head and neck pain primarily involves the ophthalmic division of the trigeminal nerve (V1). A link between systemic hypertension, pulsatile choroidal blood flow (CBF), and intraocular pressure (IOP) has been established. I propose that a trait ocular sympathetic hypofunction permits rapid episodic ocular choroidal overperfusion that stretches the ocular globe in the cohort of hypertensive patients with headache. Rapid distension of the pain-sensitive corneoscleral envelope can stimulate corneoscleral and iridial pain-sensitive V1 nerve endings and generate headache. Ocular tamponade function physiologically limits choroidal overperfusion. A higher basal IOP in some patients with moderate-to-severe hypertension may dampen pulsatile CBF and account for the negative epidemiologic link between sustained systemic hypertension and headache. Besides activation of the baroreceptor reflex, the association of hypalgesia with hypertension probably involves activation of the vasopressin-endorphin adaptive system consequent to mechanical stimulation of V1. The analogy between hypertensive headache and angle-closure glaucoma is rather limited because typical ocular and visual signs and symptoms of angle-closure glaucoma are not seen in hypertension-related headache. Hypertensive crises, including those associated with pheochromocytoma, are not accompanied by attacks of angle-closure glaucoma. Glaucoma is not associated with ocular choroidal congestion, but with reduced pulsatile CBF. The predisposition to develop angle-closure glaucoma is theoretically not associated with ocular autonomic hypofunction and should be conceptually dissociated from this hypothesis. The hypothesis can be evaluated by establishing significant circadian elevations of blood pressure, including nondipping nighttime pattern as well as circadian and periheadache measurements of IOP in patients with attacks of hypertension-related headache.