Troubled spots: Human impacts constrain the density of an apex predator inside protected areas.

Effective conservation requires understanding the processes that determine population outcomes. Too often, we assume that protected areas conserve wild populations despite evidence that they frequently fail to do so. Without large-scale studies, however, we cannot determine what relationships are the product of localized conditions versus general patterns that inform conservation more broadly. Leopards' (Panthera pardus) basic ecology is well studied but little research has investigated anthropogenic effects on leopard density at broad scales. We investigated the drivers of leopard density among 27 diverse protected areas in northeastern South Africa to understand what conditions facilitate abundant populations. We formulated 10 working hypotheses that considered the relative influence of bottom-up biological factors and top-down anthropogenic factors on leopard density. Using camera-trap survey data, we fit a multi-session spatial capture-recapture model with inhomogenous density for each hypothesis and evaluated support using an information theoretic approach. The four supported hypotheses indicated that leopard density is primarily limited by human impacts, but that habitat suitability and management conditions also matter. The proportion of camera stations that recorded domestic animals, a proxy for the extent of human impacts and protected area effectiveness, was the only predictor variable present in all four supported models. Protected areas are the cornerstone of large felid conservation, but only when the human-wildlife interface is well managed and protected areas shelter wildlife populations from anthropogenic impacts. To ensure the long-term abundance of large carnivore populations, reserve managers should recognize the ineffectiveness of "paper parks" and promote contiguous networks of protected areas that offer leopards and other large mammal populations greater space and reduced human impacts.

Using Continuous-Time Spatial Capture-Recapture models to make inference about animal activity patterns.

Quantifying the distribution of daily activity is an important component of behavioral ecology. Historically, it has been difficult to obtain data on activity patterns, especially for elusive species. However, the development of affordable camera traps and their widespread usage has led to an explosion of available data from which activity patterns can be estimated.Continuous-time spatial capture-recapture (CT SCR) models drop the occasion structure seen in traditional spatial and nonspatial capture-recapture (CR) models and use the actual times of capture. In addition to estimating density, CT SCR models estimate expected encounters through time. Cyclic splines can be used to allow flexible shapes for modeling cyclic activity patterns, and the fact that SCR models also incorporate distance means that space-time interactions can be explored. This method is applied to a jaguar dataset.Jaguars in Belize are most active and range furthest in the evening and early morning and when they are located closer to the network of trails. There is some evidence that females have a less variable pattern than males. The comparison between sexes demonstrates how CT SCR can be used to explore hypotheses about animal behavior within a formal modeling framework.SCR models were developed primarily to estimate and model density, but the models can be used to explore processes that interact across space and time, especially when using the CT SCR framework that models the temporal dimension at a finer resolution.

A spatially explicit capture-recapture estimator for single-catch traps.

Single-catch traps are frequently used in live-trapping studies of small mammals. Thus far, a likelihood for single-catch traps has proven elusive and usually the likelihood for multicatch traps is used for spatially explicit capture-recapture (SECR) analyses of such data. Previous work found the multicatch likelihood to provide a robust estimator of average density. We build on a recently developed continuous-time model for SECR to derive a likelihood for single-catch traps. We use this to develop an estimator based on observed capture times and compare its performance by simulation to that of the multicatch estimator for various scenarios with nonconstant density surfaces. While the multicatch estimator is found to be a surprisingly robust estimator of average density, its performance deteriorates with high trap saturation and increasing density gradients. Moreover, it is found to be a poor estimator of the height of the detection function. By contrast, the single-catch estimators of density, distribution, and detection function parameters are found to be unbiased or nearly unbiased in all scenarios considered. This gain comes at the cost of higher variance. If there is no interest in interpreting the detection function parameters themselves, and if density is expected to be fairly constant over the survey region, then the multicatch estimator performs well with single-catch traps. However if accurate estimation of the detection function is of interest, or if density is expected to vary substantially in space, then there is merit in using the single-catch estimator when trap saturation is above about 60%. The estimator's performance is improved if care is taken to place traps so as to span the range of variables that affect animal distribution. As a single-catch likelihood with unknown capture times remains intractable for now, researchers using single-catch traps should aim to incorporate timing devices with their traps.

The effect of features of the metabolic syndrome on atherosclerotic risk in relatively long-surviving patients with type 1 diabetes.

BACKGROUND: Increasing numbers of patients with type 1 diabetes (T1DM) are developing features of the metabolic syndrome. The additional effect of this on the development of atherosclerosis, as inferred by the carotid artery intima media thickness (IMT), has not previously been assessed. The aim of this study was to assess the effect of features of the metabolic syndrome on carotid artery IMT in a cohort of long-surviving patients with T1DM. METHODS: Long-surviving patients with T1DM attending the Centre for Diabetes and Endocrinology were assessed regarding their risk factor profile. All underwent measurement of carotid artery IMT. In all, 156 patients who had T1DM for more than 18 years had their carotid artery IMT measured. All had been attending the clinic for over 10 years, and past clinical and laboratory records were available. RESULTS: A total of 37 patients had metabolic syndrome according to the International Diabetes Federation (IDF) definition. Those with metabolic syndrome had a significantly increased carotid artery IMT (P = 0.003) compared to those without the syndrome. There was a significant relationship between the number of features of metabolic syndrome and increased atherosclerotic risk according to the carotid artery IMT (P = 0.01). A significant correlation was found between carotid artery IMT and both waist circumference (P < 0.001) and insulin resistance (P = 0.005). CONCLUSIONS: In long-surviving patients with T1DM, those that develop metabolic syndrome are more likely to have thicker carotid artery IMT, and, by inference, be at higher risk of atherosclerosis and possibly cardiovascular disease. A linear relationship was present between both waist circumference and insulin resistance and carotid artery IMT.

Nonlinear mixed effects modeling of gametocyte carriage in patients with uncomplicated malaria.

BACKGROUND: Gametocytes are the sexual form of the malaria parasite and the main agents of transmission. While there are several factors that influence host infectivity, the density of gametocytes appears to be the best single measure that is related to the human host's infectivity to mosquitoes. Despite the obviously important role that gametocytes play in the transmission of malaria and spread of anti-malarial resistance, it is common to estimate gametocyte carriage indirectly based on asexual parasite measurements. The objective of this research was to directly model observed gametocyte densities over time, during the primary infection. METHODS: Of 447 patients enrolled in sulphadoxine-pyrimethamine therapeutic efficacy studies in South Africa and Mozambique, a subset of 103 patients who had no gametocytes pre-treatment and who had at least three non-zero gametocyte densities over the 42-day follow up period were included in this analysis. RESULTS: A variety of different functions were examined. A modified version of the critical exponential function was selected for the final model given its robustness across different datasets and its flexibility in assuming a variety of different shapes. Age, site, initial asexual parasite density (logged to the base 10), and an empirical patient category were the co-variates that were found to improve the model. CONCLUSIONS: A population nonlinear modeling approach seems promising and produced a flexible function whose estimates were stable across various different datasets. Surprisingly, dihydrofolate reductase and dihydropteroate synthetase mutation prevalence did not enter the model. This is probably related to a lack of power (quintuple mutations n = 12), and informative censoring; treatment failures were withdrawn from the study and given rescue treatment, usually prior to completion of follow up.

Association between psychopathology and substance use among school-going adolescents in Cape Town, South Africa.

Limited information exists regarding the association between psychopathology and specific substance use in young people both globally and locally. We examined the association between psychopathology and substance use in high school students to determine the nature of the associations and the role of demographic factors in these associations. Grade 8 (N=480) and Grade 11 (N=459) students from 39 high schools in Cape Town, South Africa, completed a self-administered questionnaire. Psychopathology information was obtained from total scores on the Harvard Trauma Questionnaire, Beck Depression Inventory and the Zung Self-Rating Anxiety Scale. Lifetime prevalence rates were calculated for tobacco, alcohol, cannabis and inhalant use. Associations between psychopathology and substance use were determined using regression analyses and structural equation modeling. On adjusting for demographic characteristics, significant associations were found between PTSD and all substance use, between depression, alcohol, cannabis and inhalant use, and between anxiety and cannabis use. The associations of PTSD and depression with alcohol and cannabis use, and between anxiety and cannabis use, were moderated by grade. Although psychopathology and substance use were associated with each other, these associations occurred in accordance with substance and grade. Roles for gender, age and ethnicity emerged in the associations, but further investigation is recommended to examine these.

Predictive factors for rebleeding and death in alcoholic cirrhotic patients with acute variceal bleeding: a multivariate analysis.

BACKGROUND: Bleeding from esophageal varices is a leading cause of death in alcoholic cirrhotic patients. The aim of the present single-center study was to identify risk factors predictive of variceal rebleeding and death within 6 weeks of initial treatment. METHODS: Univariate and multivariate analyses were performed on 310 prospectively documented alcoholic cirrhotic patients with acute variceal hemorrhage (AVH) who underwent 786 endoscopic variceal injection treatments between January 1984 and December 2006. All injections were administered during the first 6 weeks after the patients were treated for their first variceal bleed. RESULTS: Seventy-five (24.2%) patients experienced a rebleed, 38 within 5 days of the initial treatment and 37 within 6 weeks of their initial treatment. Of the 15 variables studied and included in a multivariate analysis using a logistic regression model, a bilirubin level >51 mmol/l and transfusion of >6 units of blood during the initial hospital admission were predictors of variceal rebleeding within the first 6 weeks. Seventy-seven (24.8%) patients died, 29 (9.3%) within 5 days and 48 (15.4%) between 6 and 42 days after the initial treatment. Stepwise multivariate logistic regression analysis showed that six variables were predictors of death within the first 6 weeks: encephalopathy, ascites, bilirubin level >51 mmol/l, international normalized ratio (INR) >2.3, albumin <25 g/l, and the need for balloon tube tamponade. CONCLUSIONS: Survival was influenced by the severity of liver failure, with most deaths occurring in Child-Pugh grade C patients. Patients with AVH and encephalopathy, ascites, bilirubin levels >51 mmol/l, INR >2.3, albumin <25 g/l and who require balloon tube tamponade are at increased risk of dying within the first 6 weeks. Bilirubin levels >51 mmol/l and transfusion of >6 units of blood were predictors of variceal rebleeding.

Carotid artery intima-media complex thickening in patients with relatively long-surviving type 1 diabetes mellitus.

OBJECTIVE: The factors responsible for premature coronary atherosclerosis in patients with type 1 diabetes are ill defined. We therefore assessed carotid intima-media complex thickness (IMT) in relatively long-surviving patients with type 1 diabetes as a marker of atherosclerosis and correlated this with traditional risk factors. DESIGN: Cross-sectional study of 148 patients with relatively long-surviving (>18 years) type 1 diabetes (76 men and 72 women) attending the Centre for Diabetes and Endocrinology, Johannesburg. METHODS: The mean common carotid artery IMT and presence or absence of plaque was evaluated by high-resolution B-mode ultrasound. Their median age was 48 years and duration of diabetes 26 years (range 18-59 years). Traditional risk factors (age, duration of diabetes, glycemic control, hypertension, smoking and lipoprotein concentrations) were recorded. Three response variables were defined and modeled. Standard multiple regression was used for a continuous IMT variable, logistic regression for the presence/absence of plaque and ordinal logistic regression to model three categories of "risk." RESULTS: The median common carotid IMT was 0.62 mm (range 0.44-1.23 mm) with plaque detected in 28 cases. The multiple regression model found significant associations between IMT and current age (P=.001), duration of diabetes (P=.033), BMI (P=.008) and diagnosed hypertension (P=.046) with HDL showing a protective effect (P=.022). Current age (P=.001) and diagnosed hypertension (P=.004), smoking (P=.008) and retinopathy (P=.033) were significant in the logistic regression model. Current age was also significant in the ordinal logistic regression model (P<.001), as was total cholesterol/HDL ratio (P<.001) and mean HbA(1c) concentration (P=.073). CONCLUSIONS: The major factors influencing common carotid IMT in patients with relatively long-surviving type 1 diabetes are age, duration of diabetes, existing hypertension and HDL (protective) with a relatively minor role ascribed to relatively long-standing glycemic control.