Population responses to observed climate variability across multiple organismal groups

A major challenge in ecology is to understand how populations are affected by increased climate variability. Here, we assessed the effects of observed climate variability on different organismal groups (amphibians, insects, mammals, herbaceous plants and reptiles) by estimating the extent to which interannual variation in the annual population growth rates (CVλ) and the absolute value of the long-term population growth rate (|log λ|) were associated with short-term climate variability. We used empirical data (≥ 20 consecutive years of annual abundances) from 59 wild populations in the Northern Hemisphere, and quantified variabilities in population growth rates and climatic conditions (temperature and precipitation in active and inactive seasons) calculated over four- and eight-year sliding time windows. We observed a positive relationship between the variability of growth rate (CVλ) and the variability of temperature in the active season at the shorter timescale only. Moreover, |log λ| was positively associated with the variability of precipitation in the inactive season at both timescales. Otherwise, the direction of the relationships between population dynamics and climate variability (if any) depended largely on the season and organismal group in question. Both CVλ and |log λ| correlated negatively with species’ lifespan, indicating general differences in population dynamics between short-lived and long-lived species that were not related to climate variability. Our results suggest that although temporal variation in population growth rates and the magnitude of long-term population growth rates are partially associated with short-term interannual climate variability, demographic responses to climate fluctuations might still be population-specific rather than specific to given organismal groups, and driven by other factors than the observed climate variability

Examination of stick-slip scenario on lubricated spring-brake systems

Several complex mechanisms can be responsible for undesirable friction-induced vibrations in many mechanical systems. This paper presents a tribological and dynamic analysis of the stick-slip problem, under greased lubrication, taking into account the practical application of a spring-brake system used in electric tubular motors. The main functioning of these brakes is based on the frictional greased contact between a stationary cylinder and a torsional spring, which rotates inside it. The identification of the parameters that most affect the stick-slip appearance in greased contacts requires a complete understanding and appropriate analysis of the entire system, to identify the effects of all physical parameters on the system. Here the global dynamics and the local contact behaviour is analysed, providing an in-depth examination of the stick-slip phenomenon on a greased contact

Using Bayesian mark-recapture modelling to quantify the strength and duration of post-release effects in reintroduced populations

Translocated animals often suffer elevated mortality during some acclimation period after release. Such post-release effects must be accounted for when estimating normal survival rates and therefore predicting population persistence. The standard approach for doing this is to nominate a fixed acclimation period, and either i) exclude survival data over that period, or ii) use model selection criteria to test whether survival differs over that period. We present a more flexible approach where the acclimation period is treated as unknown and is estimated simultaneously with the pre- and post-acclimation survival probabilities. We illustrate this approach using survival data for six reintroduced populations involving three New Zealand forest bird species. Analyses of the complete data sets (22–73 surveys conducted over 4–14 years) indicated that significant post-release effects occurred in at least one sex in five of the six populations, with 30–84% mortality attributable to post-release effects over acclimation periods ranging from 1 to 9 months. When we applied the approach to just the first year of data for each population, the estimated normal survival rates were consistent with those obtained from the complete data sets, and always at least as accurate as our previous approach of excluding data up to the next breeding season after translocation. The flexible approach therefore appears to be effective for accounting for post-release effects in survival estimation, and is beneficial in quantifying both the strength and duration of those effects so that pre- and post-release management strategies are better informed

AIDS-defining events and deaths in HIV-infected children and adolescents on antiretrovirals: a 14-year study in Thailand

BACKGROUND: Data are scarce on the long-term clinical outcomes of perinatally HIV-infected children and adolescents receiving antiretroviral therapy (ART) in low/middle-income countries. We assessed the incidence of mortality before (early) and after (late) 6-month of ART and of the composite outcome of new/recurrent AIDS-defining-event or death >6 months after ART start (late AIDS/death) and their associated factors. METHODS: Study population was perinatally HIV-infected children (≤18 years) initiating ART within the Program for HIV Prevention and Treatment observational cohort (NCT00433030). Factors associated with late AIDS/death were assessed using competing risk regression models accounting for loss-to-follow-up, and included baseline and time-updated variables. RESULTS: Among 619 children, "early" mortality incidence was 99 deaths per 1000-PYFU (95%CI; 69-142) and "late" mortality 6 per 1000-PYFU (95%CI; 4-9). Of the 553 children alive >6 months after ART initiation, median age at ART initiation was 6.4 years, CD4% 8.2% and HIV-RNA 5.1 log10 copies/mL. 38 (7%) children developed late AIDS/death after median time of 3.3 years: 24 died and 24 experienced new/recurrent AIDS-defining-events (10 subsequently died). Factors independently associated with late AIDS/death were: current age ≥13 years (adjusted sub-distribution hazard-ratio 4.9; 95%CI; 2.4-10.1), HIV-RNA always ≥400 copies/mL (12.3; 4.0-37.6), BMI-z-score always <-2 SD (13.7; 3.4-55.7), and hemoglobin <8g/dL at least once (4.6; 2.0-10.5). CONCLUSIONS: After the initial 6 months of ART, being an adolescent, persistent viremia, poor nutritional status and severe anemia were associated with poor clinical outcomes. This supports the need for novel interventions that target children, particularly adolescents with poor growth and uncontrolled viremia

Height and timing of growth spurt during puberty in young people living with vertically acquired HIV in Europe and Thailand.

OBJECTIVE: The aim of this study was to describe growth during puberty in young people with vertically acquired HIV. DESIGN: Pooled data from 12 paediatric HIV cohorts in Europe and Thailand. METHODS: One thousand and ninety-four children initiating a nonnucleoside reverse transcriptase inhibitor or boosted protease inhibitor based regimen aged 1-10 years were included. Super Imposition by Translation And Rotation (SITAR) models described growth from age 8 years using three parameters (average height, timing and shape of the growth spurt), dependent on age and height-for-age z-score (HAZ) (WHO references) at antiretroviral therapy (ART) initiation. Multivariate regression explored characteristics associated with these three parameters. RESULTS: At ART initiation, median age and HAZ was 6.4 [interquartile range (IQR): 2.8, 9.0] years and -1.2 (IQR: -2.3 to -0.2), respectively. Median follow-up was 9.1 (IQR: 6.9, 11.4) years. In girls, older age and lower HAZ at ART initiation were independently associated with a growth spurt which occurred 0.41 (95% confidence interval 0.20-0.62) years later in children starting ART age 6 to 10 years compared with 1 to 2 years and 1.50 (1.21-1.78) years later in those starting with HAZ less than -3 compared with HAZ at least -1. Later growth spurts in girls resulted in continued height growth into later adolescence. In boys starting ART with HAZ less than -1, growth spurts were later in children starting ART in the oldest age group, but for HAZ at least -1, there was no association with age. Girls and boys who initiated ART with HAZ at least -1 maintained a similar height to the WHO reference mean. CONCLUSION: Stunting at ART initiation was associated with later growth spurts in girls. Children with HAZ at least -1 at ART initiation grew in height at the level expected in HIV negative children of a comparable age

Mistrust in marriage-Reasons why men do not accept couple HIV testing during antenatal care- a qualitative study in eastern Uganda

<p>Abstract</p> <p>Background</p> <p>A policy for couple HIV counseling and testing was introduced in 2006 in Uganda, urging pregnant women and their spouses to be HIV tested together during antenatal care (ANC). The policy aims to identify HIV-infected pregnant women to prevent mother-to-child transmission of HIV through prophylactic antiretroviral treatment, to provide counseling, and to link HIV-infected persons to care. However, the uptake of couple testing remains low. This study explores men's views on, and experiences of couple HIV testing during ANC.</p> <p>Methods</p> <p>The study was conducted at two time points, in 2008 and 2009, in the rural Iganga and Mayuge districts of eastern Uganda. We carried out nine focus group discussions, about 10 participants in each, and in-depth interviews with 13 men, all of whom were fathers. Data were collected in the local language, Lusoga, audio-recorded and thereafter translated and transcribed into English and analyzed using content analysis.</p> <p>Results</p> <p>Men were fully aware of the availability of couple HIV testing, but cited several barriers to their use of these services. The men perceived their marriages as unstable and distrustful, making the idea of couple testing unappealing because of the conflicts it could give rise to. Further, they did not understand why they should be tested if they did not have symptoms. Finally, the perceived stigmatizing nature of HIV care and rude attitudes among health workers at the health facilities led them to view the health facilities providing ANC as unwelcoming. The men in our study had several suggestions for how to improve the current policy: peer sensitization of men, make health facilities less stigmatizing and more male-friendly, train health workers to meet men's needs, and hold discussions between health workers and community members.</p> <p>Conclusions</p> <p>In summary, pursuing couple HIV testing as a main avenue for making men more willing to test and support PMTCT for their wives, does not seem to work in its current form in this region. HIV services must be better adapted to local gender systems taking into account that incentives, health-seeking behavior and health system barriers differ between men and women.</p