bluuebunny/crossref_metadata_2025 huggingface dataset:
Contribution of sensory feedback to ongoing ankle extensor activity during the stance phase of walking
Authors: Donelan J Maxwell , Pearson Keir G
Published: November 2004

Numerous investigations over the past 15 years have demonstrated that sensory feedback plays a critical role in establishing the timing and magnitude of muscle activity during walking. Here we review recent studies reporting that sensory feedback makes a substantial contribution to the activation of extensor motoneurons during the stance phase. Quantitative analysis of the effects of loading and unloading ankle extensor muscles during walking on a horizontal surface has shown that sensory feedback can increase the activity of ankle extensor muscles by up to 60%. There is currently some uncertainty about which sensory receptors are responsible for this enhancement of extensor activity, but likely candidates are the secondary spindle endings in the ankle extensors of humans and the Golgi tendon organs in the ankle extensors of humans and cats. Two important issues arise from the finding that sensory feedback from the leg regulates the magnitude of extensor activity. The first is the extent to which differences in the magnitude of activity in extensor muscles during different locomotor tasks can be directly attributed to changes in the magnitude of sensory signals, and the second is whether the enhancement of extensor activity is determined primarily by feedback from a specific group of receptors or from numerous groups of receptors distributed throughout the leg. Limitations of current experimental strategies prevent a straightforward empirical resolution of these issues. A potentially fruitful approach in the immediate future is to develop models of the known and hypothesized neuronal networks controlling motoneuronal activity, and use these simulations to control forward dynamic models of the musculo-skeletal system. These simulations would help understand how sensory signals are modified with a change in locomotor task and, in conjunction with physiological experiments, establish the extent to which these modifications can account for changes in the magnitude of motoneuronal activity.Key words: walking, sensory feedback, proprioceptors, pattern generation.
Somatosensory paths proceeding to spinal cord and brain — centripetal and centrifugal control for human movement
Authors: Brooke John D
Published: November 2004

The flow of fast-conducting somatosensory information proceeding from the human leg, and entering sensorimotor control processes, is modulated according to the demands of limb movement. Both centripetal (proceeding in from sensory receptor discharge) and centrifugal (proceeding out from motor control centres) convergences can cause modulation, as seen in human, dog, and cat studies. Spinal H-reflexes appear to be strongly centripetally modulated in magnitude, as do initial somatosensory-evoked potentials recorded from the scalp following transmission in fast-conducting afferents from the leg. From the brain and from locomotor pattern-generators, there is also centrifugal control onto fast-conducting somatosensory pathways from the leg, both serving spinal reflexes and ascending to the brain. One expression of the centrifugal control appears to be pattern-generator modulation of cutaneous reflexes. Centrifugal control also can be seen premovement, as spinal H-reflex facilitation. Further, it can be observed as reduction of reception at somatosensory cerebral cortex, when motor learning has occurred or when stimuli are less salient for the task. Fourteen research developments have been identified that involve the generalizability of effects, specific mechanisms, and somatosensory modulation in predictive control.Key words: feedback, feedforward, modulation, prediction, somatosensory evoked potential (SEP), H-reflex.
Anatomical organization of motoneurons and interneurons in the mudpuppy (Necturus maculosus) brachial spinal cord: the neural substrate for central pattern generation
Authors: Jovanovic Ksenija , Burke Robert E
Published: November 2004

The isolated brachial spinal cord of the mudpuppy is useful for studies of neural networks underlying forelimb locomotion, but information about its anatomy is scarce. We addressed this issue by combining retrograde labeling with fluorescent tracers and confocal microscopy. Remarkably, the central region of gray matter was aneural and contained only a tenuous meshwork of glial fibers and large extracellular spaces. Somata of motoneurons (MNs) and interneurons (INs), labeled retrogradely from ventral roots or axons in the ventro-lateral funiculus, respectively, were confined within a gray neuropil layer abutting the white matter borders, while their dendrites projected widely throughout the white matter. A considerable fraction of labeled INs was found contralaterally with axons crossing beneath a thick layer of ependyma surrounding the central canal. Dorsal roots (DRs) produced dense presynaptic arbors within a restricted dorsal region containing afferent terminations, within which dorsally directed MN and IN dendrites mingled with dense collections of synaptic boutons. Our data suggest that a major fraction of synaptic interactions takes place within the white matter. This study provides a detailed foundation for electrophysiological experiments aimed at elucidating the neural circuits involved in locomotor pattern generation.Key words: interneurons, motoneurons, sub-pial plexus, central pattern generator for locomotion.
Therapy of paretic arm in hemiplegic subjects augmented with a neural prosthesis: A cross-over study
Authors: Popovic Dejan B , Popovic Mirjana B , Sinkjær Thomas , Stefanovic Aleksandra , Schwirtlich Laszlo
Published: November 2004

There are indications that both intensive exercise and electrical stimulation have a beneficial effect on arm function in post-stroke hemiplegic patients. We recommend the use of Functional Electrical Therapy (FET), which combines electrical stimulation of the paretic arm and intensive voluntary movement of the arm to exercise daily functions. FET was applied 30 min daily for 3 weeks. Forty-one acute hemiplegics volunteered in the 18-months single blinded cross-over study (CoS). Nineteen patients (Group A) participated in FET during their acute hemiplegia, and 22 patients (Group B) participated in FET during their chronic phase of hemiplegia. Group B patients were controls during FET in acute hemiplegia, and Group A patients were controls during the FET in chronic hemiplegia. Thirty-two patients completed the study. The outcomes of the Upper Extremity Function Test (UEFT) were used to assess the ability of patients to functionally use objects, as were the Drawing Test (DT) (used to assesse the coordination of the arm), the Modified Ashworth Scale, the range of movement, and the questionnaire estimating the patients' satisfaction with the usage of the paretic arm. Patients who participated in the FET during the acute phase of hemiplegia (Group A) reached functionality of the paretic arm, on average, in less than 6 weeks, and maintained this near-normal use of the arm and hand throughout the follow-up. The gains in all outcome scores were significantly larger in Group A after FET and at all follow-ups compared with the scores before the treatment. The gains in patients who participated in the FET in the chronic phase of hemiplegia (Group B) were measurable, yet not significant. The speed of recovery was larger during the period of the FET compared with the follow-up period. The gains in Group A were significantly larger compared with the gains in Group B. The FET greatly promotes the recovery of the paretic arm if applied during the acute phase of post-stroke hemiplegia.Key words: stroke, hemiplegia, cross-over study, electrical stimulation, intensive exercise.
Basal ganglia neural mechanisms of natural movement sequences
Authors: Aldridge J Wayne , Berridge Kent C , Rosen Alyssa R
Published: November 2004

Natural rodent grooming and other instinctive behavior serves as a natural model of complex movement sequences. Rodent grooming has syntactic (rule-driven) sequences and more random movement patterns. Both incorporate the same movements—only the serial structure differs. Recordings of neural activity in the dorsolateral striatum and the substantia nigra pars reticulata indicate preferential activation during syntactic sequences over more random sequences. Neurons that are responsive during syntactic grooming sequences are often unresponsive or have reverse activation profiles during kinematically similar movements that occur in flexible or random grooming sequences. Few neurons could be categorized as strictly movement related—instead they were activated only in the context of particular sequential patterns of movements. Particular sequential patterns included "syntactic chain" grooming sequences of paw, head, and body movements and also "warm-up" sequences, which consist of head and body/limb movements that precede locomotion after a period of quiet resting (Golani 1992). Activation during warm-up was less intense and less frequent than during grooming sequences, but both sequences activated neurons above baseline levels, and the same neurons sometimes responded to both sequences. The fact that striatal neurons code 2 natural sequences which are made up of different constituent movements suggests that the basal ganglia may have a generalized role in sequence control. The basal ganglia are modulated by the context of the sequence and may play an executive function in the complex natural patterns of sequenced behaviour.Key words: movement, basal ganglia, striatum, movement sequences, sensorimotor behaviour.
Gait acts as a gate for reflexes from the foot
Authors: Duysens J , Bastiaanse C M , Smits-Engelsman B C.M , Dietz V
Published: November 2004

During human gait, electrical stimulation of the foot elicits facilitatory P2 (medium latency) responses in TA (tibialis anterior) at the onset of the swing phase, while the same stimuli cause suppressive responses at the end of swing phase, along with facilitatory responses in antagonists. This phenomenon is called phase-dependent reflex reversal. The suppressive responses can be evoked from a variety of skin sites in the leg and from stimulation of some muscles such as rectus femoris (RF). This paper reviews the data on reflex reversal and adds new data on this topic, using a split-belt paradigm. So far, the reflex reversal in TA could only be studied for the onset and end phases of the step cycle, simply because suppression can only be demonstrated when there is background activity. Normally there are only 2 TA bursts in the step cycle, whereas TA is normally silent during most of the stance phase. To know what happens in the stance phase, one needs to have a means to evoke some background activity during the stance phase. For this purpose, new experiments were carried out in which subjects were asked to walk on a treadmill with a split-belt. When the subject was walking with unequal leg speeds, the walking pattern was adapted to a gait pattern resembling limping. The TA then remained active throughout most of the stance phase of the slow-moving leg, which was used as the primary support. This activity was a result of coactivation of agonistic and antagonistic leg muscles in the supporting leg, and represented one of the ways to stabilize the body. Electrical stimulation was given to a cutaneous nerve (sural) at the ankle at twice the perception threshold. Nine of the 12 subjects showed increased TA activity during stance phase while walking on split-belts, and 5 of them showed pronounced suppressions during the first part of stance when stimuli were given on the slow side. It was concluded that a TA suppressive pathway remains open throughout most of the stance phase in the majority of subjects. The suggestion was made that the TA suppression increases loading of the ankle plantar flexors during the loading phase of stance.Key words: human gait, cutaneous reflexes, sural nerve, tibialis anterior, split belt, reflex reversal.
Cross-bridge mechanisms underlying the history-dependent properties of muscle spindles and stretch reflexes
Authors: Nichols T Richard , Cope Timothy C
Published: November 2004

The effects of prior movement on the force responses of skeletal muscle are compared with the effects of movement history on the changes in firing rate of muscle spindle receptors. Prior release results in the linearization of the mechanical properties of skeletal muscles, which can be provisionally explained by cross-bridge models of muscular contraction. The history-dependence of responses of muscle spindle receptors in unanesthetized decerebrate preparations appears to result from the kinetics of cycling and noncycling cross-bridges. The results of this comparison indicate that the integration of mechanical properties of muscle and spindle receptor promotes stiffness regulation.Key words: predictive control, muscular stiffness, muscle receptors, reflex compensation, cross-bridge cycling, nonlinear mechanical properties, feline motor control.
Motor unit firing rates during isometric voluntary contractions performed at different muscle lengths
Authors: Del Valle Alejandro , Thomas Christine K
Published: November 2004

Firing rates of motor units and surface EMG were measured from the triceps brachii muscles of able-bodied subjects during brief submaximal and maximal isometric voluntary contractions made at 5 elbow joint angles that covered the entire physiological range of muscle lengths. Muscle activation at the longest, midlength, and shortest muscle lengths, measured by twitch occlusion, averaged 98%, 97%, and 93% respectively, with each subject able to achieve complete activation during some contractions. As expected, the strongest contractions were recorded at 90° of elbow flexion. Mean motor unit firing rates and surface EMG increased with contraction intensity at each muscle length. For any given absolute contraction intensity, motor unit firing rates varied when muscle length was changed. However, mean motor unit firing rates were independent of muscle length when contractions were compared with the intensity of the maximal voluntary contraction (MVC) achieved at each joint angle.Key words: muscle activation, length–tension relationships, force–frequency relationships.
A BRIEF REVIEW OF THE SEARCH FOR ISOLATABLE FRACTIONAL CHARGE ELEMENTARY PARTICLES
Authors: PERL MARTIN L. , LEE ERIC R. , LOOMBA DINESH
Published: November 2004

Since the initial measurements of the electron charge a century ago, experimenters have faced the persistent question as to whether elementary particles exist that have charges that are fractional multiples of the electron charge. In the standard model of particle physics the quarks are such particles, but it is assumed that quarks cannot be individually isolated, the quarks always being confined inside hadrons. This paper is a brief review of the present status of searches for isolatable fractional charge particles such as a lepton-like particle with fractional charge or an unconfined quark. There have been a very large number of searches but there is no confirmed evidence for existence of isolatable fractional charge particles. It may be that they do not exist, but it is also possible that they are very massive or that their production mechanisms are very small so that they have been missed by existing searches. Therefore the aim of this review is to urge (a) the invention of ways to substantially increase the range of known search methods and (b) to urge the invention of new search methods for isolatable fractional charge particles.
TOWARDS A MULTIFRACTAL PARADIGM OF STOCHASTIC VOLATILITY?
Authors: BOITOUT NICOLAS , URECHE-RANGAU LOREDANA
Published: November 2004

This paper examines the behavior of volatility and trading volume in an extended Mixture-of-Distribution Hypothesis framework. According to this Hypothesis, both volatility and volume are subordinated to the same latent, stochastic variable: the information flow. One way to enlarge this modeling in order to capture long range dependecies observed in these two variables is to use multi-component volatility models. However, traditional multi-component volatility models seem no longer enough to describe the more complex behavior of the volatility. This is why we introduce in this class of models, a stochastic cascade model of volatility, inherited from the multifractal paradigm. In the empirical section we provide some evidence in favor of this approach. Both volatility and volume are fractionally integrated processes with similar hyperbolic decay rates, but the long range dependence of their power transforms exhibits significant differences. Moreover, we emphasize the existence of lagged cross-correlations between the volatilities at different sampling frequencies, first pointed out by Müller et al. [59], which historically opened the door to a (stochastic) cascade scheme of the volatility in the literature. A multiscaling analysis of the structure functions (generalized volatilities) confirms this result. The empirical results are provided with data on the French stock Alcatel.
TIME-VARYING RISK PREMIA IN EMERGING MARKETS: EXPLANATION BY A MULTI-FACTOR AFFINE TERM STRUCTURE MODEL
Authors: DE ALMEIDA CAIO IBSEN RODRIGUES
Published: November 2004

From the empirical viewpoint, the Expectation Hypothesis Theory (EHT) of the term structure of interest rates has been extensively tested and rejected for US term structure data. Dai and Singleton [6] show that under the settings of Affine term structure models it is possible that one matches both the historical term structure dynamics and capture an important stylized fact that have contradicted the EHT: Time-varying risk premia. In emerging markets, economic conditions tend to be much less stable than in developed markets. For this reason, if risk premia is dynamic in such markets, intuition would suggest that it is more volatile than in developed markets, implying a stronger statistical rejection of the EHT. In this paper, we verify the robustness of Dai and Singleton's results under these more extreme market conditions. We estimate an arbitrage free Affine Gaussian model for the term structure of swaps in the Brazilian market. We propose an extensive empirical analysis which consists on: defining the optimal number of factors to be used in the model, estimating the model, giving interpretation to the state variables in terms of risk factors, and studying the model implied risk premia. In the end, we propose an application for risk management of interest rates futures portfolios.
Clinical Judgment and Decision Making
Authors: Garb Howard N.
Published: November 2004

When clinical psychologists make judgments, are they likely to be correct or incorrect? The following topics are reviewed: (a) methodological advances in evaluating the validity of descriptions of personality and psychopathology, (b) recent findings on the cognitive processes of clinicians, and (c) the validity of judgments and utility of decisions made by mental health professionals. Results from research on clinical judgment and decision making and their relationship to conflicts within the field of clinical psychology are discussed.
Categorical and Dimensional Models of Personality Disorder
Authors: Trull Timothy J. , Durrett Christine A.
Published: November 2004

We review major categorical and dimensional models of personality pathology, highlighting advantages and disadvantages of these approaches. Several analytic and methodological approaches to the question of the categorical versus dimensional status of constructs are discussed, including taxometric analyses, latent class analyses, and multivariate genetic analyses. Based on our review, we advocate a dimensional approach to classifying personality pathology. There is converging evidence that four major domains of personality are relevant to personality pathology: neuroticism/negative affectivity/emotional dysregulation; extraversion/positive emotionality; dissocial/antagonistic behavior; and constraint/compulsivity/conscientiousness. Finally, we discuss how dimensional approaches might be integrated into the diagnostic system, as well as some of the major issues that must be addressed in order for dimensional approaches to gain wide acceptance.
Stress and Health: Psychological, Behavioral, and Biological Determinants
Authors: Schneiderman Neil , Ironson Gail , Siegel Scott D.
Published: November 2004

Stressors have a major influence upon mood, our sense of well-being, behavior, and health. Acute stress responses in young, healthy individuals may be adaptive and typically do not impose a health burden. However, if the threat is unremitting, particularly in older or unhealthy individuals, the long-term effects of stressors can damage health. The relationship between psychosocial stressors and disease is affected by the nature, number, and persistence of the stressors as well as by the individual's biological vulnerability (i.e., genetics, constitutional factors), psychosocial resources, and learned patterns of coping. Psychosocial interventions have proven useful for treating stress-related disorders and may influence the course of chronic diseases.
THE NORTH ANATOLIAN FAULT: A NEW LOOK
Authors: Şengör A.M.C , Tüysüz Okan , İmren Caner , Sakınç Mehmet , Eyidoğan Haluk , Görür Naci , Le Pichon Xavier , Rangin Claude
Published: November 2004

Dedicated to the memory of three pioneers, İhsan Ketin, Sırrı Erinç and Melih Tokay, and a recent student, Aykut Barka, who burnt himself out in pursuit of the mysteries of the North Anatolian Fault.

▪ Abstract  The North Anatolian Fault (NAF) is a 1200-km-long dextral strike-slip fault zone that formed by progressive strain localization in a generally westerly widening right-lateral keirogen in northern Turkey mostly along an interface juxtaposing subduction-accretion material to its south and older and stiffer continental basements to its north. The NAF formed approximately 13 to 11 Ma ago in the east and propagated westward. It reached the Sea of Marmara no earlier than 200 ka ago, although shear-related deformation in a broad zone there had already commenced in the late Miocene. The fault zone has a very distinct morphological expression and is seismically active. Since the seventeenth century, it has shown cyclical seismic behavior, with century-long cycles beginning in the east and progressing westward. For earlier times, the record is less clear but does indicate a lively seismicity. The twentieth century record has been successfully interpreted in terms of a Coulomb failure model, whereby every earthquake concentrates the shear stress at the western tips of the broken segments leading to westward migration of large earthquakes. The August 17 and November 12, 1999, events have loaded the Marmara segment of the fault, mapped since the 1999 earthquakes, and a major, M ≤ 7.6 event is expected in the next half century with an approximately 50% probability on this segment. Currently, the strain in the Sea of Marmara region is highly asymmetric, with greater strain to the south of the Northern Strand. This is conditioned by the geology, and it is believed that this is generally the case for the entire North Anatolian Fault Zone. What is now needed is a more detailed geological mapping base with detailed paleontology and magnetic stratigraphy in the shear-related basins and more paleomagnetic observations to establish shear-related rotations.
Ecological Effects of Transgenic Crops and the Escape of Transgenes into Wild Populations
Authors: Pilson Diana , Prendeville Holly R.
Published: November 2004

▪ Abstract  Ecological risks associated with the release of transgenic crops include nontarget effects of the crop and the escape of transgenes into wild populations. Nontarget effects can be of two sorts: (a) unintended negative effects on species that do not reduce yield and (b) greater persistence of the crop in feral populations. Conventional agricultural methods, such as herbicide and pesticide application, have large and well-documented nontarget effects. To the extent that transgenes have more specific target effects, transgenic crops may have fewer nontarget effects. The escape of transgenes into wild populations, via hybridization and introgression, could lead to increased weediness or to the invasion of new habitats by the wild population. In addition, native species with which the wild plant interacts (including herbivores, pathogens, and other plant species in the community) could be negatively affected by “transgenic-wild” plants. Conventional crop alleles have facilitated the evolution of increased weediness in several wild populations. Thus, some transgenes that allow plants to tolerate biotic and abiotic stress (e.g., insect resistance, drought tolerance) could have similar effects.
Spatial Synchrony in Population Dynamics
Authors: Liebhold Andrew , Koenig Walter D. , Bjørnstad Ottar N.
Published: November 2004

▪ Abstract  Spatial synchrony refers to coincident changes in the abundance or other time-varying characteristics of geographically disjunct populations. This phenomenon has been documented in the dynamics of species representing a variety of taxa and ecological roles. Synchrony may arise from three primary mechanisms:(a) dispersal among populations, reducing the size of relatively large populations and increasing relatively small ones; (b) congruent dependence of population dynamics on a synchronous exogenous random factor such as temperature or rainfall, a phenomenon known as the “Moran effect”; and (c) trophic interactions with populations of other species that are themselves spatially synchronous or mobile. Identification of the causes of synchrony is often difficult. In addition to intraspecific synchrony, there are many examples of synchrony among populations of different species, the causes of which are similarly complex and difficult to identify. Furthermore, some populations may exhibit complex spatial dynamics such as spiral waves and chaos. Statistical tests based on phase coherence and/or time-lagged spatial correlation are required to characterize these more complex patterns of spatial dynamics fully.
Ecology of Woodland Herbs in Temperate Deciduous Forests
Authors: Whigham Dennis F.
Published: November 2004

▪ Abstract  The diversity of woodland herbs is one of the most striking features of deciduous forests in the temperate zone. Here I review the literature on the ecology of woodland herbs. The review is timely because, since Paulette Bierzychudek's seminal review of the subject in 1982, a number of species have become rare or threatened owing to the conversion of forests to other land uses, competition by alien plant species, and increased abundance of native wildlife that negatively impact woodland herbs (e.g., white-tailed deer). Although the basic biology of woodland herbs is mostly known, few species have been studied in detail, and we are only able to make broad generalities about their ecology. We are especially lacking in information needed to conserve and restore species in altered and threatened habitats.
Regime Shifts, Resilience, and Biodiversity in Ecosystem Management
Authors: Folke Carl , Carpenter Steve , Walker Brian , Scheffer Marten , Elmqvist Thomas , Gunderson Lance , Holling C.S.
Published: November 2004

▪ Abstract  We review the evidence of regime shifts in terrestrial and aquatic environments in relation to resilience of complex adaptive ecosystems and the functional roles of biological diversity in this context. The evidence reveals that the likelihood of regime shifts may increase when humans reduce resilience by such actions as removing response diversity, removing whole functional groups of species, or removing whole trophic levels; impacting on ecosystems via emissions of waste and pollutants and climate change; and altering the magnitude, frequency, and duration of disturbance regimes. The combined and often synergistic effects of those pressures can make ecosystems more vulnerable to changes that previously could be absorbed. As a consequence, ecosystems may suddenly shift from desired to less desired states in their capacity to generate ecosystem services. Active adaptive management and governance of resilience will be required to sustain desired ecosystem states and transform degraded ecosystems into fundamentally new and more desirable configurations.
Ecological Impacts of Deer Overabundance
Authors: Côté Steeve D. , Rooney Thomas P. , Tremblay Jean-Pierre , Dussault Christian , Waller Donald M.
Published: November 2004

▪ Abstract  Deer have expanded their range and increased dramatically in abundance worldwide in recent decades. They inflict major economic losses in forestry, agriculture, and transportation and contribute to the transmission of several animal and human diseases. Their impact on natural ecosystems is also dramatic but less quantified. By foraging selectively, deer affect the growth and survival of many herb, shrub, and tree species, modifying patterns of relative abundance and vegetation dynamics. Cascading effects on other species extend to insects, birds, and other mammals. In forests, sustained overbrowsing reduces plant cover and diversity, alters nutrient and carbon cycling, and redirects succession to shift future overstory composition. Many of these simplified alternative states appear to be stable and difficult to reverse. Given the influence of deer on other organisms and natural processes, ecologists should actively participate in efforts to understand, monitor, and reduce the impact of deer on ecosystems.
On the Ecological Roles of Salamanders
Authors: Davic Robert D. , Welsh Hartwell H.
Published: November 2004

▪ Abstract  Salamanders are cryptic and, though largely unrecognized as such, extremely abundant vertebrates in a variety of primarily forest and grassland environments, where they regulate food webs and contribute to ecosystem resilience-resistance (= stability) in several ways: (a) As mid-level vertebrate predators, they provide direct and indirect biotic control of species diversity and ecosystem processes along grazer and detritus pathways; (b) via their migrations, they connect energy and matter between aquatic and terrestrial landscapes; (c) through association with underground burrow systems, they contribute to soil dynamics; and (d) they supply high-quality and slowly available stores of energy and nutrients for tertiary consumers throughout ecological succession. Salamanders also can provide an important service to humans through their use as cost-effective and readily quantifiable metrics of ecosystem health and integrity. The diverse ecological roles of salamanders in natural areas underscore the importance of their conservation.
Operational Criteria for Delimiting Species
Authors: Sites Jack W. , Marshall Jonathon C.
Published: November 2004

▪ Abstract  Species are routinely used as fundamental units of analysis in biogeography, ecology, macroevolution, and conservation biology. A large literature focuses on defining species conceptually, but until recently little attention has been given to the issue of empirically delimiting species. Researchers confronted with the task of delimiting species in nature are often unsure which method(s) is (are) most appropriate for their system and data type collected. Here, we review twelve of these methods organized into two general categories of tree- and nontree-based approaches. We also summarize the relevant biological properties of species amenable to empirical evaluation, the classes of data required, and some of the strengths and limitations of each method. We conclude that all methods will sometimes fail to delimit species boundaries properly or will give conflicting results, and that virtually all methods require researchers to make qualitative judgments. These facts, coupled with the fuzzy nature of species boundaries, require an eclectic approach to delimiting species and caution against the reliance on any single data set or method when delimiting species.

No one definition has as yet satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species.

     Darwin (1859/1964)
Ecological Responses to Habitat Edges: Mechanisms, Models, and Variability Explained
Authors: Ries Leslie , Fletcher Robert J. , Battin James , Sisk Thomas D.
Published: November 2004

▪ Abstract  Edge effects have been studied for decades because they are a key component to understanding how landscape structure influences habitat quality. However, making sense of the diverse patterns and extensive variability reported in the literature has been difficult because there has been no unifying conceptual framework to guide research. In this review, we identify four fundamental mechanisms that cause edge responses: ecological flows, access to spatially separated resources, resource mapping, and species interactions. We present a conceptual framework that identifies the pathways through which these four mechanisms can influence distributions, ultimately leading to new ecological communities near habitat edges. Next, we examine a predictive model of edge responses and show how it can explain much of the variation reported in the literature. Using this model, we show that, when observed, edge responses are largely predictable and consistent. When edge responses are variable for the same species at the same edge type, observed responses are rarely in opposite directions. We then show how remaining variability may be understood within our conceptual frameworks. Finally, we suggest that, despite all the research in this area, the development of tools to extrapolate edge responses to landscapes has been slow, restricting our ability to use this information for conservation and management.
Evolutionary Biology of Animal Cognition
Authors: Dukas Reuven
Published: November 2004

▪ Abstract  This review focuses on five key evolutionary issues pertaining to animal cognition, defined as the neuronal processes concerned with the acquisition, retention, and use of information. Whereas the use of information, or decision making, has been relatively well examined by students of behavior, evolutionary aspects of other cognitive traits that affect behavior, including perception, learning, memory, and attention, are less well understood. First, there is ample evidence for genetically based individual variation in cognitive traits, although much of the information for some traits comes from humans. Second, several studies documented positive association between cognitive abilities and performance measures linked to fitness. Third, information on the evolution of cognitive traits is available primarily for color vision and decision making. Fourth, much of the data on plasticity of cognitive traits appears to reflect nonadaptive phenotypic plasticity, perhaps because few evolutionary analyses of cognitive plasticity have been carried out. Nonetheless, several studies suggest that cognitive traits show adaptive plasticity, and at least one study documented genetically based individual variation in plasticity. Fifth, whereas assertions that cognition has played a central role in animal evolution are not supported by currently available data, theoretical considerations indicate that cognition may either increase or decrease the rate of evolutionary change.
The Southwest Australian Floristic Region: Evolution and Conservation of a Global Hot Spot of Biodiversity
Authors: Hopper Stephen D. , Gioia Paul
Published: November 2004

▪ Abstract  Like South Africa's Greater Cape Floristic Region, the Southwest Australian Floristic Region (SWAFR) is species rich, with a Mediterranean climate and old, weathered, nutrient-deficient landscapes. This region has 7380 native vascular plants (species/subspecies): one third described since 1970, 49% endemic, and 2500 of conservation concern. Origins are complex. Molecular phylogenies suggest multiple dispersal events into, out of, and within the SWAFR throughout the Cretaceous and Cenozoic; in many phylogenetically unrelated clades; and from many directions. Either explosive speciation or steady cladogenesis occurred among some woody sclerophyll and herbaceous families from the mid-Tertiary in response to progressive aridity. Genomic coalescence was sometimes involved. Rainforest taxa went extinct by the Pleistocene. Old lineages nevertheless persist as one endemic order (Dasypogonales) and 6–11 endemic families. Such a rich flora on old landscapes that have been exposed to European land-use practices is highly threatened. Conservation programs must minimize soil removal and use local germplasm in restoration programs.
Avian Extinctions from Tropical and Subtropical Forests
Authors: Sodhi Navjot S. , Liow L.H. , Bazzaz F.A.
Published: November 2004

▪ Abstract  Tropical forests are being lost at an alarming rate. Studies from various tropical locations report losses of forest birds as possibly direct or indirect results of deforestation. Although it may take a century for all the sensitive species to be extirpated from a site following habitat loss, species with larger or heavier bodies and those foraging on insects, fruits, or both are particularly extinction prone. Larger- or heavier-bodied species may occur at low densities, increasing their vulnerability to habitat alterations. Insectivores are vulnerable for reasons such as the loss of preferred microhabitats, poor dispersal abilities, and/or ground nesting habits that make them susceptible to predation. The lack of year-round availability of fruits may make survival in deforested or fragmented areas difficult for frugivores. Extirpation of large predators, superior competitors, pollinators, and seed dispersers may have repercussions for tropical ecosystem functioning. Large tropical reserves that adequately protect existing forest avifauna are needed. Sound ecological knowledge of tropical forest avifauna for biodiversity-friendly forest management practices is also needed but sorely lacking.
Ecological and Evolutionary Consequences of Multispecies Plant-Animal Interactions
Authors: Strauss Sharon Y. , Irwin Rebecca E.
Published: November 2004

▪ Abstract  Ecologists and evolutionary biologists are broadly interested in how the interactions among organisms influence their abundance, distribution, phenotypes, and genotypic composition. Recently, we have seen a growing appreciation of how multispecies interactions can act synergistically or antagonistically to alter the ecological and evolutionary outcomes of interactions in ways that differ fundamentally from outcomes predicted by pairwise interactions. Here, we review the evidence for criteria identified to detect community-based, diffuse coevolution. These criteria include (a) the presence of genetic correlations between traits involved in multiple interactions, (b) interactions with one species that alter the likelihood or intensity of interactions with other species, and (c) nonadditive combined effects of multiple interactors. In addition, we review the evidence that multispecies interactions have demographic consequences for populations, as well as evolutionary consequences. Finally, we explore the experimental and analytical techniques, and their limitations, used in the study of multispecies interactions. Throughout, we discuss areas in particular need of future research.
Long-Term Stasis in Ecological Assemblages: Evidence from the Fossil Record
Authors: DiMichele W.A. , Behrensmeyer A.K. , Olszewski T.D. , Labandeira C.C. , Pandolfi J.M. , Wing S.L. , Bobe R.
Published: November 2004

▪ Abstract  Studies of plant and animal assemblages from both the terrestrial and the marine fossil records reveal persistence for extensive periods of geological time, sometimes millions of years. Persistence does not require lack of change or the absence of variation from one occurrence of the assemblage to the next in geological time. It does, however, imply that assemblage composition is bounded and that variation occurs within those bounds. The principal cause for these patterns appears to be species-, and perhaps clade-level, environmental fidelity that results in long-term tracking of physical conditions. Other factors that influence persistent recurrence of assemblages are historical, biogeographic effects, the “law of large numbers,” niche differentiation, and biotic interactions. Much research needs to be done in this area, and greater uniformity is needed in the approaches to studying the problem. However, great potential also exists for enhanced interaction between paleoecology and neoecology in understanding spatiotemporal complexity of ecological dynamics.
MECHANISMS OF HOPPERBURN: An Overview of Insect Taxonomy, Behavior, and Physiology
Authors: Backus Elaine A. , Serrano Miguel S. , Ranger Christopher M.
Published: November 2004

▪ Abstract  Hopperburn is a noncontagious disease of plants caused by the direct feeding damage of certain leafhoppers and planthoppers. Although long studied, especially with Empoasca spp. leafhoppers (Cicadellidae: Typhlocybinae), the mechanisms underlying hopperburn have only recently been elucidated. Hopperburn is caused by a dynamic interaction between complex insect feeding stimuli (termed hopperburn initiation) and complex plant responses (termed the hopperburn cascade). Herein we review the nature of the feeding stimuli in hopperburn initiation, especially for Empoasca spp., which we also compare with the planthopper Nilaparvata lugens. Contrary to previous reports, Empoasca hopperburn is not caused solely by toxic saliva. Instead, it is caused by a plant wound response triggered by a unique type of stylet movement, which is then exacerbated by saliva. Electrical penetration graph monitoring has revealed that all Empoasca spp. are cell rupture feeders, not sheath feeders, and that certain tactics of that feeding strategy are more damaging than others. Measuring the proportions of the most damaging feeding led to development of a resistance index, the Stylet Penetration Index, which can predict hopperburn severity in different plants or under different environmental conditions and can supplement or replace traditional, field-based resistance indices.
THYSANOPTERA: Diversity and Interactions
Authors: Mound Laurence A.
Published: November 2004

▪ Abstract  Published literature on thrips has been dominated by descriptive taxonomy, pest control work, and generalized synecology. The lack of studies examining the detailed biology or autecology of any species limits our understanding of how thrips live and the processes underlying their diversification. Similarly, the phylogenetic inadequacy of thrips classification limits our ability to examine the evolution of biological traits. The extent to which our knowledge of the biology of thrips has increased in recent years is reviewed, such as the behavior of particular species and their interactions with other organisms, including host plant associations, pollination, predation, and natural enemies—factors involved in driving diversification within this order of opportunistic insects.
EVOLUTIONARY AND MECHANISTIC THEORIES OF AGING
Authors: Hughes Kimberly A. , Reynolds Rose M.
Published: November 2004

▪ Abstract  Senescence (aging) is defined as a decline in performance and fitness with advancing age. Senescence is a nearly universal feature of multicellular organisms, and understanding why it occurs is a long-standing problem in biology. Here we present a concise review of both evolutionary and mechanistic theories of aging. We describe the development of the general evolutionary theory, along with the mutation accumulation, antagonistic pleiotropy, and disposable soma versions of the evolutionary model. The review of the mechanistic theories focuses on the oxidative stress resistance, cellular signaling, and dietary control mechanisms of life span extension. We close with a discussion of how an approach that makes use of both evolutionary and molecular analyses can address a critical question: Which of the mechanisms that can cause variation in aging actually do cause variation in natural populations?
EVOLUTIONARY ECOLOGY OF INSECT IMMUNE DEFENSES
Authors: Schmid-Hempel Paul
Published: November 2004

▪ Abstract  Evolutionary ecology seeks to understand the selective reasons for the design features of the immune defense, especially with respect to parasitism. The molecular processes thereby set limitations, such as the failure to recognize an antigen, response specificity, the cost of defense, and the risk of autoimmunity. Sex, resource availability, and interference by parasites also affect a response. In turn, the defense repertoire consists of different kinds of immune responses—constitutive or induced, general or specific—and involves memory and lasting protection. Because the situation often defies intuition, mathematical analysis is typically required to identify the costs and benefits of variation in design, but such studies are few. In all, insect immune defense is much more similar to that of vertebrates than previously thought. In addition, the field is now rapidly becoming revolutionized by molecular data and methods that allow unprecedented access to study evolution in action.
EGG DUMPING IN INSECTS
Authors: Tallamy Douglas W.
Published: November 2004

▪ Abstract  Females that place eggs under the care of conspecifics have been labeled egg dumpers. Egg dumping is an effective reproductive alternative that lowers risks for, and has the potential to increase fecundity in, its practitioners. Although insect egg dumpers can be social parasites of the maternal behavior of egg recipients, dumping is more likely to be a viable reproductive alternative when the costs to egg recipients are low and thus the defense by potential hosts against egg dumping intrusions is minimal. These conditions are met in insects that guard only eggs or in insects whose eggs hatch into self-supporting precocial young that need little beyond defense from parents. When this is the case, egg dumping is favored by natural and/or kin selection as a mechanism by which dumpers can avoid parental risks and increase fecundity, and egg recipients can enhance offspring survival by diluting predation.
SYSTEMATICS, EVOLUTION, AND BIOLOGY OF SCELIONID AND PLATYGASTRID WASPS
Authors: Austin A.D. , Johnson N.F. , Dowton M.
Published: November 2004

▪ Abstract  The Platygastroidea comprises two families of parasitoids, Scelionidae and Platygastridae, and nearly 4500 described species. They parasitize a diverse array of insects as well as spiders. Idiobiont endoparasitism of eggs is the putative ground plan biology, as reflected by all scelionids, but most Platygastridae are koinobiont endoparasitoids of immature Auchenorrhyncha, Sternorrhyncha, and Cecidomyiidae. The superfamily is demonstrably monophyletic but its phylogenetic position remains uncertain. Relationships within the Platygastroidea are also poorly known and the group is in need of comprehensive phylogenetic study. Significant information is available on host relationships and biology, although much of this is biased to a few genera of Telenominae that are employed as biocontrol agents. Hosts for many genera are unknown, in particular those that inhabit leaf litter or parasitize solitary host eggs. The Trissolcus basalis–Nezara viridula parasitoid-host association has become a favored model system in ecological, behavioral, and physiological research on insects.