Satisfying giant appetites : mechanisms of small scale foraging by large African herbivores

Variation in body mass allows for resource partitioning and co-existence of different species. Body mass is also seen as the main factor governing nutrient requirements in herbivores as metabolic rate and requirements have often been found to scale to ¾ power of body mass. Although the consequences of body mass on foraging behaviour of herbivores has been extensively studied, the mechanism behind how body mass differences determines the small scale foraging patterns of especially larger herbivores, has up to now been unclear. In this study, I looked at how body mass and small scale vegetation characteristics shaped the mouth morphology of herbivores and how body mass of a herbivore affects the scale at which intake is maximized. The results indicate that the dilution of plant mass and more specifically leaf mass in space requires that mega-herbivores such as elephant have enlarged soft mouth parts to compensate for this dilution. Finally, I demonstrate, using linear programming techniques with multiple nutrients as constraints, how a mega-herbivore’s daily diet choice is determined by forage abundance whereas a small herbivore is more constrained by fibre

Behavioural changes in African elephants in response to wildlife tourism

Eco-tourism and human-wildlife interaction can lead to increases in stress, vigilance and aggression in many species, however, studies investigating wildlife viewing are scarce. We present the first study investigating the impact of wildlife tourism on African elephant, Loxodonta africana, behaviour. Over 15 months, we studied the effect of monthly tourist pressure (tourist numbers) on the occurrence of stress-related, vigilance and conspecific-directed aggressive behaviour in 27 individually identified elephants and the effect of up to 3 vehicles on the direction of travel of non-identified herds using five-minute continuous focal observations. We analysed the effect of tourist pressure and vehicle presence using generalised linear mixed models, including habitat type, herd type and size, and season, as well as sex and age for behaviour models, as additional factors. We found no effect of factors on stress-related behaviour, but elephants were more likely to perform vigilance behaviours at waterholes compared to other habitat types. As tourist pressure increased, conspecific-directed aggression in elephants increased and male elephants were more likely to perform conspecific directed aggression compared to female elephants. . Further, we found that elephant herds became increasingly likely to move away with increasing numbers of vehicles present. Results suggest that reserves should monitor elephant behaviour to identify when tourist pressure has potential effects on elephant welfare and train guides to monitor behaviour and adjust minimum distances flexibly to ensure high welfare standards and tourist safety. This study further contributes to a small but growing body of literature on non-consumptive wildlife tourism impacts on wild animals

Stem rust resistance in South African wheat cultivars

The aim of this study was to attempt to identify reliable factors associated with dropout risk in a sample of 161 panic disorder patients treated with manualized cognitive behavior therapy. Four possible predictors of dropout were selected from the literature: level of education, treatment motivation, personality psychopathology, and initial symptom severity. Thirty-two patients (19.9%) were dropouts. Level of education and motivation were significantly associated with dropout, but the associations were small. Personality psychopathology and initial symptom severity were not associated with dropout. It is concluded that, at present, we are unable to make precise dropout risk predictions, even in a homogeneous group of patients treated using standardized treatment

Normalized Difference Vegetation Index, temperature, and age affect faecal thyroid hormone concentrations in free-ranging African elephants.

Conservation biologists can use hormone measurements to assess animals’ welfare, reproductive state, susceptibility to stressors, as well as energy expenditure. Quantifying hormone concentrations from faecal samples is particularly advantageous as samples can be collected without disturbing animals’ behaviour. In order for an endocrine marker to be useful for wildlife managers, we need to understand how extrinsic and intrinsic factors affect hormone concentrations in free-ranging animal populations. Thyroid hormones are linked to basal metabolic rate and energy expenditure. Previous research demonstrated that triiodothyronine (T3) can be measured successfully in faecal matter of African elephants, Loxodonta africana. However, to our knowledge, research into factors affecting changes in elephant T3 levels has only been carried out in captive elephants so far. Thus, we present the first study of faecal T3 metabolite (mT3) concentrations of a large population of free-ranging African elephants. Over 15 months, we collected faecal samples from identified (n=43 samples) and unidentified (n=145 samples) individuals in Madikwe Game Reserve, South Africa. We investigated whether vegetative productivity (NDVI) in interaction with mean monthly temperature, age, and sex affected mT3 concentrations. We found a significant negative interaction effect of NDVI and temperature. Increasing NDVI was related to higher concentrations of mT3, but increasing temperature was related to a decrease in mT3 concentrations in individually identified and unidentified elephants. In unidentified individuals, juvenile elephants had significantly higher mT3 concentrations compared to adult elephants. Faecal T3 can successfully be quantified in samples from free-ranging elephant populations and thus provides insight into energy expenditure in large herbivores

A refined baseline methodology for large scale lighting retrofit projects

Abstract: The residential sector is one of the major consumers of energy produced in the world. According to International Energy Balances (IEA, 2013), the residential sector demand represents about a quarter of the primary energy used in the world. Therefore, most energy efficiency programmes targeting large savings on a national or regional level pay particular attention to the opportunities in the residential sector. Lighting retrofitting on a large number of sites constitutes one of the most used strategies of energy conservation in the residential sector. However, given the large number of sites involved in this type of project, conventional measurement and verification (M&V) techniques based on the audit of each site, are not cost effective. Often, a statistical assessment approach based on the audit of a limited number of sites is the methodology used to mitigate the cost and the logistical challenges associated with the project. The major challenge in projects of this nature is to accurately estimate the energy consumption of a large number of sites using the measurement performed on a sample of sites selected from the overall population. In this research, baseline methodologies used in a selected number of light retrofitting projects have been analysed and, based on the observations made during this analysis, some improvements are suggested. The proposed methodology has been tested on a number of residences located on the premises of the University of Johannesburg. This paper describes the existing baseline methodologies and presents the improvements suggested to enhance the credibility of M&V results. The key results of the experimental phase of this project are also presented in this paper

An exact solution for 2+1 dimensional critical collapse

We find an exact solution in closed form for the critical collapse of a scalar field with cosmological constant in 2+1 dimensions. This solution agrees with the numerical simulation done by Pretorius and Choptuik of this system.Comment: 5 pages, 5 figures, Revtex. New comparison of analytic and numerical solutions beyond the past light cone of the singularity added. Two new references added. Error in equation (21) correcte

The Interpretations For the Low and High Frequency QPO Correlations of X-ray Sources Among White Dwarfs, Neutron Stars and Black Holes

It is found that there exists an empirical linear relation between the high frequency \nhigh and low frequency \nlow of quasi-periodic oscillations (QPOs) for black hole candidate (BHC), neutron star (NS) and white dwarf (WD) in the binary systems, which spans five orders of magnitude in frequency. For the NS Z (Atoll) sources, $\nu_{high}$ and $\nu_{low}$ are identified as the lower kHz QPO frequency and horizontal branch oscillations (HBOs) \nh (broad noise components); for the black hole candidates and low-luminosity neutron stars, they are the QPOs and broad noise components at frequencies between 1 and 10 Hz; for WDs, they are the ``dwarf nova oscillations'' (DNOs) and QPOs of cataclysmic variables (CVs). To interpret this relation, our model ascribes $\nu_{high}$ to the Alfv\'en wave oscillation frequency at a preferred radius and $\nu_{low}$ to the same mechanism at another radius. Then, we can obtain \nlow = 0.08 \nhigh and the relation between the upper kHz QPO frequency \nt and HBO to be \nh \simeq 56 ({\rm Hz}) (\nt/{\rm kHz})^{2}, which are in accordance with the observed empirical relations. Furthermore, some implications of model are discussed, including why QPO frequencies of white dwarfs and neutron stars span five orders of magnitude in frequency. \\Comment: 11 pages, 1 figure, accepted by PAS

Thrombin-Fibrinogen In Vitro Flow Model of Thrombus Growth in Cerebral Aneurysms

Cerebral aneurysms are balloon-like structures that develop on weakened areas of cerebral artery walls, with a significant risk of rupture. Thrombi formation is closely associated with cerebral aneurysms and has been observed both before and after intervention, leading to a wide variability of outcomes in patients with the condition. The attempt to manage the outcomes has led to the development of various computational models of cerebral aneurysm thrombosis. In the current study, we developed a simplified thrombin-fibrinogen flow system, based on commercially available purified human-derived plasma proteins, which enables thrombus growth and tracking in an idealized cerebral aneurysm geometry. A three-dimensional printed geometry of an idealized cerebral aneurysm and parent vessel configuration was developed. An unexpected outcome was that this phantom-based flow model allowed us to track clot growth over a period of time, by using optical imaging to record the progression of the growing clot into the flow field. Image processing techniques were subsequently used to extract important quantitative metrics from the imaging dataset, such as end point intracranial thrombus volume. The model clearly demonstrates that clot formation, in cerebral aneurysms, is a complex interplay between mechanics and biochemistry. This system is beneficial for verifying computational models of cerebral aneurysm thrombosis, particularly those focusing on initial angiographic occlusion outcomes, and will also assist manufacturers in optimizing interventional device designs

Generalized harmonic formulation in spherical symmetry

In this pedagogically structured article, we describe a generalized harmonic formulation of the Einstein equations in spherical symmetry which is regular at the origin. The generalized harmonic approach has attracted significant attention in numerical relativity over the past few years, especially as applied to the problem of binary inspiral and merger. A key issue when using the technique is the choice of the gauge source functions, and recent work has provided several prescriptions for gauge drivers designed to evolve these functions in a controlled way. We numerically investigate the parameter spaces of some of these drivers in the context of fully non-linear collapse of a real, massless scalar field, and determine nearly optimal parameter settings for specific situations. Surprisingly, we find that many of the drivers that perform well in 3+1 calculations that use Cartesian coordinates, are considerably less effective in spherical symmetry, where some of them are, in fact, unstable.Comment: 47 pages, 15 figures. v2: Minor corrections, including 2 added references; journal version

Robustness of slow contraction to cosmic initial conditions

We present numerical relativity simulations of cosmological scenarios in which the universe is smoothed and flattened by undergoing a phase of slow contraction and test their sensitivity to a wide range of initial conditions. Our numerical scheme enables the variation of all freely specifiable physical quantities that characterize the initial spatial hypersurface, such as the initial shear and spatial curvature contributions as well as the initial field and velocity distributions of the scalar that drives the cosmological evolution. In particular, we include initial conditions that are far outside the perturbative regime of the well-known attractor scaling solution. We complement our numerical results by analytically performing a complete dynamical systems analysis and show that the two approaches yield consistent results.Comment: 41 pages, 18 figures; accepted for publication in JCA