On net reproductive rate and the timing of reproductive output

Abstract: Understanding the relationship between life-history patterns and population growth is central to demographic studies. Here we derive a new method for calculating the timing of reproductive output, from which the generation time and its variance can also be calculated. The method is based on the explicit computation of the net reproductive rate (R0) using a new graphical approach. Using nodding thistle, desert tortoise, creeping aven, and cat's ear as examples, we show how R0 and the timing of reproduction is calculated and interpreted, even in cases with complex life cycles. We show that the explicit R0 formula allows us to explore the effect of all reproductive pathways in the life cycle, something that cannot be done with traditional analysis of the population growth rate (lambda). Additionally, we compare a recently published method for determining population persistence conditions with the condition R0 > 1 and show how the latter is simpler and more easily interpreted biologically. Using our calculation of the timing of reproductive output, we illustrate how this demographic measure can be used to understand the effects of life-history traits on population growth and control.

Allee effects, invasion pinning, and species' borders

All species' ranges are the result of successful past invasions. Thus, models of species' invasions and their failure can provide insight into the formation of a species' geographic range. Here, we study the properties of invasion models when a species cannot persist below a critical population density known as an "Allee threshold." In both spatially continuous reaction-diffusion models and spatially discrete coupled ordinary-differential-equation models, the Allee effect can cause an invasion to fail. In patchy landscapes (with dynamics described by the spatially discrete model), range limits caused by propagation failure (pinning) are stable over a wide range of parameters, whereas, in an uninterrupted habitat (with dynamics described by a spatially continuous model), the zero velocity solution is structurally unstable and thus unlikely to persist in nature. We derive conditions under which invasion waves are pinned in the discrete space model and discuss their implications for spatially complex dynamics, including critical phenomena, in ecological landscapes. Our results suggest caution when interpreting abrupt range limits as stemming either from competition between species or a hard environmental limit that cannot be crossed: under a wide range of plausible ecological conditions, species' ranges may be limited by an Allee effect. Several example systems appear to fit our general model.

Storage of household firearms: an examination of the attitudes and beliefs of married women with children

Although safe firearm storage is a promising injury prevention strategy, many parents do not keep their firearms unloaded and locked up. Using the theory of planned behavior as a guiding conceptual framework, this study examines factors associated with safe storage among married women with children and who have firearms in their homes. Data come from a national telephone survey (n=185). We examined beliefs about defensive firearm use, subjective norms, perceived behavioral control and firearm storage practices. A Wilcoxon-Mann-Whitney test was conducted to assess associations between psychosocial factors and firearm storage practices. Women were highly motivated to keep firearms stored safely. Those reporting safe storage practices had more favorable attitudes, more supportive subjective norms and higher perceptions of behavioral control than those without safe storage. One-fourth believed a firearm would prevent a family member from being hurt in case of a break-in, 58% believed a firearm could scare off a burglar. Some 63% said they leave decisions about firearm storage to their husbands. Women were highly motivated to store firearms safely as evidenced by favorable attitudes, supportive subjective norms and high perceptions of behavioral control. This was especially true for those reporting safer storage practices.

Demography of renal disease in childhood

The demography of renal failure in childhood is examined through an analysis of the UK Renal Registry data on patients in established renal failure (ERF) and studies of chronic kidney disease populations. The predominant cause is renal dysplasia and related conditions. Congenital obstructive uropathy is the third largest group overall and the second in early childhood. Males predominate in both these groups. Antenatal diagnoses are frequently not made despite routine scanning. Those children, who present to nephrology after the age of 3 months without an antenatal diagnosis, progress to ERF later than those diagnosed antenatally. Discrepancies exist between the demography of antenatal diagnoses and those seen postnatally. This is likely to represent the limitations of antenatal ultrasound as a diagnostic screening tool.

Patient perceptions about illness self-management in ANCA-associated small vessel vasculitis

OBJECTIVES

To characterize patient perceptions, related to eight self-management behaviours relevant for adults with ANCA-associated small vessel vasculitis (ANCA-SVV), and to determine if these perceptions were associated with performance of each behaviour.

METHODS

Adults with ANCA-SVV (n = 202) completed a self-administered questionnaire that assessed eight self-management behaviours (adherence to recommendations for medication, health service use, diet, exercise, infection avoidance and symptom monitoring; prompt reporting of symptoms and side effects; and adjusting activities in response to symptoms), perceptions about these behaviours, socio-demographics, clinical factors and social desirability bias. Descriptive statistics were generated to characterize patients' perceptions about difficulty of, importance of, and specific barriers to performing each behaviour. Regression analyses explored whether these variables were associated with performing each behaviour, controlling for potential confounders.

RESULTS

With few exceptions, higher perceived importance and lower perceived difficulty of each behaviour were associated with more frequent performance of the behaviour. For each behaviour, several specific barriers were frequently endorsed by patients and a number of these were associated with lower levels of self-management.

CONCLUSION

This study reveals that patient perceptions about the illness and its treatment influence ANCA-SVV self-management. Perceived barriers to medication, health services, diet and exercise adherence were similar to those in other illnesses. This study also provides insight into barriers experienced by patients in performing behaviours (infection avoidance, symptom monitoring, reporting symptoms and side-effects and adjusting activities) not often previously studied. How the identification of these barriers can help inform future interventions for ANCA-SVV patients is to be discussed.

Cardiovascular outcomes among sildenafil users: results of the International Men's Health Study

AIM

To assess the incidence of serious cardiovascular disease (CVD) events [i.e. myocardial infarction (MI) and stroke] and all-cause mortality in men with erectile dysfunction (ED) who received prescriptions for sildenafil.

METHODS

The International Men's Health Study (IMHS) was a prospective, observational cohort study of patients with ED and a new or existing prescription for sildenafil. Baseline and follow-up questionnaires provided information on demographics, CVD risk factors and ED. Postevent questionnaires were mailed to patients following possible nonfatal CVD events to collect information related to exposure to sildenafil/ED treatments before the event.

RESULTS

Thirty-five CVD events were reported in 30 patients in the analysis set (n = 3813). The incidence of all-cause mortality, MI and stroke was 0.4, 0.6 and 0.1 per 100 patient-years of observation respectively. Among the six men who reported using sildenafil in the month before a nonfatal CVD event, two reported use in the 24 h before the event.

CONCLUSION

The results of the IMHS support previous reports that ED and CVD are often comorbid and share risk factors.

Probabilistic neural networks modeling of the 48-h LC50 acute toxicity endpoint to Daphnia magna

Two modeling experiments based on the maximum likelihood estimation paradigm and targeting prediction of the Daphnia magna 48-h LC50 acute toxicity endpoint for both organic and inorganic compounds are reported. The resulting models computational algorithms are implemented as basic probabilistic neural networks with Gaussian kernel (statistical corrections included). The first experiment uses strictly D. magna information for 971 structures as training/learning data and the resulting model targets practical applications. The second experiment uses the same training/learning information plus additional data on another 29 compounds whose endpoint information is originating from D. pulex and Ceriodaphnia dubia. It only targets investigation of the effect of mixing strictly D. magna 48-h LC50 modeling information with small amounts of similar information estimated from related species, and this is done as part of the validation process. A complementary 81 compounds dataset (involving only strictly D. magna information) is used to perform external testing. On this external test set, the Gaussian character of the distribution of the residuals is confirmed for both models. This allows the use of traditional statistical methodology to implement computation of confidence intervals for the unknown measured values based on the models predictions. Examples are provided for the model targeting practical applications. For the same model, a comparison with other existing models targeting the same endpoint is performed.

Outcome of Henoch-Schönlein purpura nephritis treated with long-term immunosuppression

This retrospective study investigated the outcome of 27 children (19 male) with Henoch-Schönlein purpura nephritis (HSN) of International Study of Kidney Disease in Children (ISKDC) grade 3b or higher treated with long-term immunosuppressive therapy in a single centre over a 10-year period. The mean age at presentation was 9.7 years. The median estimated glomerular filtration rate (eGFR) was 91.3 ml/min per 1.73 m(2), with the median urine protein creatinine ratio (UP:UC) 556 mg/mmol. The treatment protocol comprised daily steroids and cyclophosphamide for 8-12 weeks followed by azathioprine and a reducing regimen of alternate-day steroids for 8-12 months. After a mean follow-up period of 7 years following presentation, 37% made a complete recovery, 40.7% had persistent proteinuria, 7.4% had persistent proteinuria and were on antihypertensive therapy and 14.8% had progressed to end-stage kidney failure (ESKF). Children with poor outcome were older at presentation (p 0.005), had more crescents (p 0.015) and had heavier proteinuria 6 months post initial biopsy (p 0.023). All of the four children with ESKF had nephrotic range proteinuria and greater than 50% crescents on initial biopsy. Despite long-term immunosuppression, the majority of children with HSN grade 3b or higher will have persistent renal abnormalities on long-term follow-up.

Complex spatial group patterns result from different animal communication mechanisms

We present previously undescribed spatial group patterns that emerge in a one-dimensional hyperbolic model for animal group formation and movement. The patterns result from the assumption that the interactions governing movement depend not only on distance between conspecifics, but also on how individuals receive information about their neighbors and the amount of information received. Some of these patterns are classical, such as stationary pulses, traveling waves, ripples, or traveling trains. However, most of the patterns have not been reported previously. We call these patterns zigzag pulses, semizigzag pulses, breathers, traveling breathers, and feathers.

Accuracy of ultrasonic detection of renal scarring in different centres using DMSA as the gold standard

BACKGROUND

There is an ongoing debate over the radiological investigations of children with urinary tract infections (UTIs) with some authorities suggesting that ultrasound scan (USS) alone is an accurate tool to diagnose renal parenchymal scarring post-pyelonephritis. All studies on this subject have been performed at paediatric teaching centres whereas most children with UTIs are managed by General Paediatricians in District General Hospitals (DGHs) in the United Kingdom. We wished to identify whether results of scans in DGHs differed from those in teaching centres.

METHODS

We looked at all children with a clinical history of UTIs having a DMSA and USS over a one year period in two DGHs and one teaching centre. A total of 476 children's results were reviewed, 297 from the DGHs and 179 from the teaching centre.

RESULTS

The cohort had a total of 949 renal units. There were 79 scarred renal units (kidneys) on DMSA (8%) in 72 patients (15%). Just 18 renal units were detected as being scarred on USS (22.8%). Nine of 32 scarred renal units in the teaching centre were detected compared with nine of 47 in the DGHs (P = 0.40). Thirty-nine (49%) of the scarred renal units were in patients >5-years old. Of these 12 (30.7%) were detected on USS, nine of 17 within the teaching centre compared with just three of 22 at the DGHs (P = 0.01).

CONCLUSION

Overall only a small percentage of scars are detected on USS. In the over 5-year old group, where USS alone might be preferred, DGHs were significantly worse at detecting scarred kidneys. We conclude that if the detection of renal scars is a prime reason for imaging in children with UTIs, ultrasonography alone is inappropriate at any age and DMSA ought to be the primary investigation.

Biological Control Through Intraguild Predation: Case Studies in Pest Control, Invasive Species and Range Expansion

Intraguild predation (IGP), the interaction between species that eat each other and compete for shared resources, is ubiquitous in nature. We document its occurrence across a wide range of taxonomic groups and ecosystems with particular reference to non-indigenous species and agricultural pests. The consequences of IGP are complex and difficult to interpret. The purpose of this paper is to provide a modelling framework for the analysis of IGP in a spatial context. We start by considering a spatially homogeneous system and find the conditions for predator and prey to exclude each other, to coexist and for alternative stable states. Management alternatives for the control of invasive or pest species through IGP are presented for the spatially homogeneous system. We extend the model to include movement of predator and prey. In this spatial context, it is possible to switch between alternative stable steady states through local perturbations that give rise to travelling waves of extinction or control. The direction of the travelling wave depends on the details of the nonlinear intraguild interactions, but can be calculated explicitly. This spatial phenomenon suggests means by which invasions succeed or fail, and yields new methods for spatial biological control. Freshwater case studies are used to illustrate the outcomes.

A new method for calculating net reproductive rate from graph reduction with applications to the control of invasive species

Matrix models are widely used for demographic analysis of age and stage structured biological populations. Dynamic properties of the model can be summarized by the net reproductive rate R (0). In this paper, we introduce a new method to calculate and analyze the net reproductive rate directly from the life cycle graph of the matrix. We show, with examples, how our method of analysis of R (0) can be used in the design of strategies for controlling invasive species.

Modeling Group Formation and Activity Patterns in Self-Organizing Collectives of Individuals

We construct and analyze a nonlocal continuum model for group formation with application to self-organizing collectives of animals in homogeneous environments. The model consists of a hyperbolic system of conservation laws, describing individual movement as a correlated random walk. The turning rates depend on three types of social forces: attraction toward other organisms, repulsion from them, and a tendency to align with neighbors. Linear analysis is used to study the role of the social interaction forces and their ranges in group formation. We demonstrate that the model can generate a wide range of patterns, including stationary pulses, traveling pulses, traveling trains, and a new type of solution that we call zigzag pulses. Moreover, numerical simulations suggest that all three social forces are required to account for the complex patterns observed in biological systems. We then use the model to study the transitions between daily animal activities that can be described by these different patterns.

National survey of doses from CT in the UK: 2003

A review of patient doses from CT examinations in the UK for 2003 has been conducted on the basis of data received from over a quarter of all UK scanners, of which 37% had multislice capability. Questionnaires were employed to collect scan details both for the standard protocols established at each scanner for 12 common types of CT examination on adults and children, and for samples of individual patients. This information was combined with published scanner-specific CT dose index (CTDI) coefficients to estimate values of the standard dose indices CTDI(w) and CTDI(vol) for each scan sequence. Knowledge of each scan length allowed assessment of the dose-length product (DLP) for each examination, from which effective doses were then estimated. When compared with a previous UK survey for 1991, wide variations were still apparent between CT centres in the doses for standard protocols. The mean UK doses for adult patients were in general lower by up to 50% than those for 1991, although doses were slightly higher for multislice (4+) (MSCT) relative to single slice (SSCT) scanners. Values of CTDI(vol) for MSCT were broadly similar to European survey data for 2001. The third quartile values of these dose distributions have been used to derive UK national reference doses for examinations on adults (separately for SSCT and MSCT) and children as initial tools for promoting patient protection. The survey has established the PREDICT (Patient Radiation Exposure and Dose in CT) database as a sustainable national resource for monitoring dose trends in CT through the ongoing collation of further survey data.

Diabetes mellitus following paediatric renal transplantation: a single centre experience

BACKGROUND/AIMS

Post-transplant diabetes mellitus (PTDM) has a variably reported incidence of 4-41% among adults and children. We describe our recent experience of four children with PTDM in a paediatric renal transplantation centre.

METHODS

We undertook a retrospective analysis of the glycaemic status of all paediatric patients undergoing renal transplantation at our centre in the 2-year study period. The clinical features and investigations of those who developed PTDM were further reviewed.

RESULTS

Five episodes of PTDM occurred in 4/32 children. There was a variable onset and a wide range of symptoms. Investigations revealed a combination of insulinopenia with peripheral insulin resistance. Insulin therapy was required for variable durations with resolution of PTDM in four episodes. PTDM did not adversely affect the renal graft function.

CONCLUSION

PTDM requires increased awareness among paediatric nephrologists and endocrinologists for early recognition and prompt effective intervention.

An evaluation of the quality of commercially produced patient information leaflets

AIM

A descriptive study was undertaken to assess the quality of a range of patient information leaflets produced by the British Dental Association.

METHOD

Twenty-nine leaflets were assessed with regard to presentation, readability and quality. The topic areas covered included: treatment, self-care and disease related information. Presentation was evaluated with regard to layout, font size, typeface, use of illustrations, paper type and print colour. Readability was assessed using the Flesch reading grade and the SMOG reading grade. Quality was assessed using the DISCERN tool.

FINDINGS

All leaflets scored quite well for readability, with the average SMOG Reading Grade Level being 9.10 (SD 0.80) and the average Flesch reading Grade Level being 6.18 (SD 0.83). There were, however, some areas of presentation that could be improved, specifically font size, illustration use and paper finish, which did not comply with the RNIB guidelines. Quality ratings using the DISCERN tool were low. In particular most leaflets scored poorly in setting out clear aims in the opening paragraph, in identifying sources and dates of information provided, and other sources of advice and support available. Few leaflets discussed the option of no treatment or how the treatment would affect overall quality of life. The role of shared decision making was rarely mentioned.

CONCLUSION

Patient information leaflets produced commercially are of high production quality and good readability but tend not to be patient centred.

Nurse bullying: organizational considerations in the maintenance and perpetration of health care bullying cultures

AIM

To examine bullying within nursing from a micro-sociological perspective and elucidate interactive mechanisms contributing to its causes and continuation within the nursing profession.

BACKGROUND

The paper is part of a doctoral research study into bullying within nursing. It considers issues pertinent to management, and in the role of negotiated interactions within the National Health Service when dealing with bullying problems. The complex dynamics involved can be problematic for management when dealing with bullying, while often managers have been targets of bullying themselves and not infrequently accused of it. Features of bullying activity are explored, along with issues of target and bully awareness, a central feature in bullying negotiations. Issues of awareness and emergence of bullying behaviour have been identified through vignettes and unstructured interviews, and the research has identified complex interactive events in the creation and maintenance of nurse bullying activity. It is hoped that with a clearer understanding of such mechanisms and manifestations that bullying in the workplace can be reduced or eliminated. The paper is of practical use to nurse managers in illuminating such mechanisms and bringing bullying awareness to the fore. Such activity is ultimately damaging to the organization in both cost and time; and significant for professional practice by its impact upon the nurse and their work in supportive and safe environments. It will also to allow managers to consider their own practice and reactions to bullying activity within the profession.

CONCLUSIONS

The overall findings from the research point strongly to bullying activity being essentially 'learned behaviour' within the workplace rather than any predominantly psychological deficit within individual perpetrators and targets.

Potential role of natural enemies during tree range expansions following climate change

Recent investigations have shown how chance, long-range dispersal events can allow tree populations to migrate rapidly in response to changes in climate. However, this apparent solution to Reid's paradox applies solely within the context of single species models, while the rapid migration rates seen in pollen records occurred within multispecies communities. Ecologists are therefore presented with a new challenge: reconciling the macroscopic dynamics of spread seen in the pollen record with the rules and interactions governing plant community assembly. A case that highlights this issue is the rapid spread of Beech during the Holocene into a landscape already dominated by a close competitor, Hemlock. In this study, we analyse a simple model of plant community assembly incorporating competition for space and dispersal dynamics, showing how, even when a species is capable of rapid migration into an empty landscape, the presence of an ecologically similar competitor causes Reid's paradox to re-emerge because of the dramatic slowing effect of competitive interactions on a species' rate of spread. We then show how the answer to the question of how tree species dispersed rapidly into occupied landscapes may lie in secondary interactions with host-specific pathogens and parasites. Inclusion of host-specific pathogens into the simple community assembly model illustrates how tree species undergoing range expansions can temporarily outstrip specialist predators, giving rise to a transient Jansen-Connell effect, in which the invader acts as temporary 'super-species' that spreads rapidly into communities already occupied by competitors at rates consistent with those observed in the paleo-record.

Sustained correction of glycogen storage disease type II using adeno-associated virus serotype 1 vectors

Glycogen storage disease type II (GSDII) is caused by a lack of functional lysosomal acid alpha-glucosidase (GAA). Affected individuals store glycogen in lysosomes beginning during gestation, ultimately resulting in fatal hypertrophic cardiomyopathy and respiratory failure. We have assessed the utility of recombinant adeno-associated virus (rAAV) vectors to restore GAA activity in vivo in a mouse model of GSDII (Gaa(-/-)). A single systemic administration of a rAAV serotype 1 (rAAV1) vector to neonate animals resulted in restored cardiac GAA activity to 6.4 times the normal level (mean=641+/-190% of normal (Gaa(+/+)) levels with concomitant glycogen clearance) at 11 months postinjection. Greater than 20% of normal levels of GAA activity were also observed in the diaphragm and quadriceps muscles. Furthermore, functional correction of the soleus skeletal muscle was also observed compared to age-matched untreated Gaa(-/-) control animals. These results demonstrate that rAAV1 vectors can mediate sustained therapeutic levels of correction of both skeletal and cardiac muscles in a model of fatal cardiomyopathy and muscular dystrophy.

Percutaneous real-time ultrasound-guided renal biopsy by automated biopsy gun in children: safety and complications

BACKGROUND

Percutaneous renal biopsy under real time ultrasound guidance is a routine procedure in pediatric nephrology and allows a histological diagnosis to be made in children with evidence of renal disease.

METHODS

Retrospective case note review.

RESULTS

Over four years 191 renal biopsies were attempted in 116 patients; 186 biopsies were performed successfully: 102 native and 84 renal allografts. 151 renal biopsies were performed under sedation and 34 biopsies were performed under general anesthetic, one biopsy without sedation. Problems during sedation were recorded in 5/151 (3.3%) cases. All patients remained in hospital overnight for observation following the biopsy. Complications were reported in 23/185 (12%) of biopsies. Macroscopic hematuria was recorded in 13/185 (7%), presenting within 6-hours of biopsy, on first void, in 11 patients. Two patients developed macroscopic hematuria four and six days after the procedure. One patient with macroscopic hematuria required a single blood transfusion. Three patients developed urinary retention requiring catheterization for up to 48 hours post-procedure, two of whom also had macroscopic hematuria. Pain post procedure was reported in 7.6% episodes and was reported significantly more often with elective native biopsies.

CONCLUSIONS

Renal biopsy can safely be performed as a day care procedure, if patients are observed for six hours instead of 24-hours post biopsy.

Long-term outcome of meningococcal sepsis-associated acute renal failure

SETTING

Twenty-one of 209 children admitted to the intensive care unit with meningococcal septicemia developed oliguric acute renal failure necessitating renal replacement therapy.

PATIENTS

Twelve survivors underwent renal assessment at a median of 4.2 yrs postpresentation.

RESULT

Two had abnormal glomerular filtration rate, proteinuria, and hypertension; one had isolated proteinuria; and one had an isolated renal parenchymal defect on DMSA scan.

CONCLUSION

Long-term follow-up of this population is recommended.

Hormone replacement therapy: pathobiological aspects of hormone-sensitive cancers in women relevant to epidemiological studies on HRT: a mini-review

Hormone replacement therapy (HRT) has gained widespread and in some areas indiscriminate use. In reference to recent epidemiological studies which showed unexpected and controversial associations of HRT use with malignant tumours, here we review the current understanding of the dynamics of tumour growth. The pathomorphological characteristics and sex hormone sensitivity of cancers of the breast, endometrium, ovary and colon are discussed. The development of cancer from the first malignant tumour cell to clinical diagnosis takes many years. Hormones can influence tumour growth, but it is questionable whether hormones induce malignant tumours de novo. It is much more likely that hormones 'merely' promote the growth of already existing tumour cells. The long developmental process of tumours is in apparent contradiction to results of some epidemiological studies that describe an increased cancer risk, implying primary initiation, in HRT users within observation periods of 1-6 years. The mechanisms of initiation versus promotion of hormone-sensitive cancers, particularly breast cancer, are only partly understood. The conventional methods of epidemiological studies cannot detect potential risk factors without bias if they do not include a pathomorphological component on growth characteristics. The results of previous studies should be interpreted with great caution with regard to tumour biology.

Persistence, spread and the drift paradox

We derive conditions for persistence and spread of a population where individuals are either immobile or dispersing by advection and diffusion through a one-dimensional medium with a unidirectional flow. Reproduction occurs only in the stationary phase. Examples of such systems are found in rivers and streams, marine currents, and areas with prevalent wind direction. In streams, a long-standing question, dubbed 'the drift paradox', asks why aquatic insects faced with downstream drift are able to persist in upper stream reaches. For our two-phase model, persistence of the population is guaranteed if, at low population densities, the local growth rate of the stationary component of the population exceeds the rate of entry of individuals into the drift. Otherwise the persistence condition involves all the model parameters, and persistence requires a critical (minimum) domain size. We calculate the rate at which invasion fronts propagate up- and downstream, and show that persistence and ability to spread are closely connected: if the population cannot advance upstream against the flow, it also cannot persist on any finite spatial domain. By studying two limiting cases of our model, we show that residence in the immobile state always enhances population persistence. We use our findings to evaluate a number of mechanisms previously proposed in the ecological literature as resolutions of the drift paradox.