169 research outputs found
Assessing the camera trap methodologies used to estimate density of unmarked populations
1. Population density estimations are essential for wildlife management and conservation. Camera traps have become a promising cost-effective tool, for which several methods have been described to estimate population density when individuals are unrecognizable (i.e. unmarked populations). However, comparative tests of their applicability and performance are scarce.
2. Here, we have compared three methods based on camera traps to estimate population density without individual recognition: Random Encounter Model (REM), Random Encounter and Staying Time (REST) and Distance Sampling with camera traps (CT-DS). Comparisons were carried out in terms of consistency with one another, precision and cost-effectiveness. We considered six natural populations with a wide range of densities, and three species with different behavioural traits (red deer Cervus elaphus, wild boar Sus scrofa and red fox Vulpes vulpes). In three of these populations, we obtained independent density estimates as a reference.
3. The densities estimated ranged from 0.23 individuals/km2 (fox) to 34.87 individuals/km2 (red deer). We did not find significant differences in terms of density values estimated by the three methods in five out of six populations, but REM has a tendency to generate higher average density values than REST and CT-DS. Regarding the independents’ densities, REM results were not significantly different in any population, and REST and CT-DS were significantly different in one population. The precision obtained was not significantly different between methods, with average coefficients of variation of 0.28 (REST), 0.36 (REM) and 0.42 (CT-DS). The REST method required the lowest human effort.
4. Synthesis and applications. Our results show that all of the methods examined can work well, with each having particular strengths and weaknesses. Broadly, Random Encounter and Staying Time (REST) could be recommended in scenarios of high abundance, Distance Sampling with camera traps (CT-DS) in those of low abundance while Random Encounter Model (REM) can be recommended when camera trap performance is not optimal, as it can be applied with less risk of bias. This broadens the applicability of camera trapping for estimating densities of unmarked populations using information exclusively obtained from camera traps. This strengthens the case for scientifically based camera trapping as a cost-effective method to provide reference estimates for wildlife managers, including within multi-species monitoring programmes
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Need for and requirements for neutron irradiation facility for fusion materials testing
The construction and operation of an intense 14MeV neutron source is essential for the development and eventual qualification of structural materials for a fusion reactor demonstration plant (DEMO). Because of the time required for materials developed and the scale-up of materials to commercial production, a decision to build a neutron source should precede engineering design activities for a DEMO by at least 20 years. The characteristic features of 14MeV neutron damage are summarized including effects related to cascade structure, transmutation production, and dose rate. The importance of a 14MeV neutron source for addressing fundamental radiation damage issues, alloy development activities and the development of an engineering data bases is discussed. From these considerations the basic requirements and machine parameters are derived. 14 refs., 5 figs., 5 tabs
Density responses of lesser-studied carnivores to habitat and management strategies in southern Tanzania's Ruaha-Rungwa landscape.
Compared to emblematic large carnivores, most species of the order Carnivora receive little conservation attention despite increasing anthropogenic pressure and poor understanding of their status across much of their range. We employed systematic camera trapping and spatially explicit capture-recapture modelling to estimate variation in population density of serval, striped hyaena and aardwolf across the mixed-use Ruaha-Rungwa landscape in southern Tanzania. We selected three sites representative of different habitat types, management strategies, and levels of anthropogenic pressure: Ruaha National Park’s core tourist area, dominated by Acacia-Commiphora bushlands and thickets; the Park’s miombo woodland; and the neighbouring community-run MBOMIPA Wildlife Management Area, also covered in Acacia-Commiphora. The Park’s miombo woodlands supported a higher serval density (5.56 [Standard Error = ±2.45] individuals per 100 km2) than either the core tourist area (3.45 [±1.04] individuals per 100 km2) or the Wildlife Management Area (2.08 [±0.74] individuals per 100 km2). Taken together, precipitation, the abundance of apex predators, and the level of anthropogenic pressure likely drive such variation. Striped hyaena were detected only in the Wildlife Management Area and at low density (1.36 [±0.50] individuals per 100 km2), potentially due to the location of the surveyed sites at the edge of the species’ global range, high densities of sympatric competitors, and anthropogenic edge effects. Finally, aardwolf were captured in both the Park’s core tourist area and the Wildlife Management Area, with a higher density in the Wildlife Management Area (13.25 [±2.48] versus 9.19 [±1.66] individuals per 100 km2), possibly as a result of lower intraguild predation and late fire outbreaks in the area surveyed. By shedding light on three understudied African carnivore species, this study highlights the importance of miombo woodland conservation and community-managed conservation, as well as the value of by-catch camera trap data to improve ecological knowledge of lesser-studied carnivores
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Structure and composition of phases occurring in austenitic stainless steels in thermal and irradiation environments
Transmission electron diffraction techniques coupled with quantitative x-ray energy dispersive spectroscopy have been used to characterize the phases which develop in austenitic stainless steels during exposure to thermal and to irradiation environments. In AISI 316 and Ti-modified stainless steels some thirteen phases have been identified and characterized in terms of their crystal structure and chemical composition. Irradiation does not produce any completely new phases. However, as a result of radiation-induced segregation principally of Ni and Si, and of enhanced diffusion rates, several major changes in phase relationships occur during irradiation. Firstly, phases characteristic of remote regions of the phase diagram appear unexpectedly and dissolve during postirradiation annealing (radiation-induced phases). Secondly, some phases develop with their compositions significantly altered by the incorporation of Ni or Si (radiation-modified phases)
Variance of bioimpedance analysis measurements with physicalactivity and ingestion of food and water
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Leopard Panthera pardus density in southern Mozambique: evidence from spatially explicit capture-recapture in Xonghile Game Reserve
Rigorous status estimates of populations of large carnivores are necessary to inform their management and help evaluate the effectiveness of conservation interventions. The African leopard Panthera pardus faces rising anthropogenic pressures across most of its contracting sub-Saharan range, but the scarcity of reliable population estimates means that management decisions often have to rely on expert opinion rather than being based on sound evidence. This is particularly true for Mozambique, where little is known about the ecology or conservation status of leopard populations as a result of prolonged armed conflict. We used camera trapping and spatially explicit capture-recapture models to provide a leopard density estimate in Xonghile Game Reserve in southern Mozambique, which is part of the Greater Limpopo Transfrontier conservation initiative. The estimated population density was 2.60 +/- SE 0.96 leopards/100 km(2). Our study provides a baseline leopard density for the region and the first empirical density estimate for southern Mozambique. Our results also suggest that current methods used to set trophy hunting quotas for leopards, both in Mozambique and elsewhere in Africa, may be leading to unsustainable quotas, which highlights the importance of robust empirical data in guiding conservation policy
Leopard Panthera pardus density in southern Mozambique: evidence from spatially explicit capture–recapture in Xonghile Game Reserve
Rigorous status estimates of populations of large carnivores are necessary to inform their management and help evaluate the effectiveness of conservation interventions. The African leopard Panthera pardus faces rising anthropogenic pressures across most of its contracting sub-Saharan range, but the scarcity of reliable population estimates means that management decisions often have to rely on expert opinion rather than being based on sound evidence. This is particularly true for Mozambique, where little is known about the ecology or conservation status of leopard populations as a result of prolonged armed conflict. We used camera trapping and spatially explicit capture–recapture models to provide a leopard density estimate in Xonghile Game Reserve in southern Mozambique, which is part of the Greater Limpopo Transfrontier conservation initiative. The estimated population density was 2.60 ± SE 0.96 leopards/100 km2. Our study provides a baseline leopard density for the region and the first empirical density estimate for southern Mozambique. Our results also suggest that current methods used to set trophy hunting quotas for leopards, both in Mozambique and elsewhere in Africa, may be leading to unsustainable quotas, which highlights the importance of robust empirical data in guiding conservation policy
Adaptação e validação das sub-escalas de controlo flexÃvel e rÃgido do comportamento alimentar
[resumo][abstract
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Control of helium effects in irradiated materials based on theory and experiment
Helium produced in materials by (n,..cap alpha..) transmutation reactions during neutron irradiations or subjected in ion bombardment experiments causes substantial changes in the response to displacement damage. In particular, swelling, phase transformations and embrittlement are strongly affected. Present understanding of the mechanisms underlying these effects is reviewed. Key theoretical relationships describing helium effects on swelling and helium diffusion are described. Experimental data in the areas of helium effects on swelling and precipitation is reviewed with emphasis on critical experiments that have been designed and evaluated in conjunction with theory. Confirmed principles for alloy design to control irradiation performance are described
Combining local knowledge and occupancy analysis for a rapid assessment of forest elephants in Cameroon’s timber production forests
Information on the distribution and abundance of the forest elephant Loxodonta cyclotis is needed to allocate limited resources appropriately and set conservation goals for the species. However, monitoring at large scales in forest habitats is complicated, expensive and time consuming. We investigated the potential of applying interview-based occupancy analysis as a tool for the rapid assessment of the distribution and relative abundance of forest elephants in eastern Cameroon. Using single-season occupancy models, we explored the covariates that affect forest elephant occupancy and detectability, and identified spatial and temporal patterns in population change and occupancy. Quantitative and qualitative socio-demographic data offer additional depth and understanding, placing the occupancy analysis in context and providing valuable information to guide conservation action. Detectability of forest elephants has decreased since 2008, which is consistent with the decline in perceived abundance in occupied sites. Forest elephants occupy areas outside protected areas and outside the known elephant range defined by IUCN. Critical conservation attention is required to assess forest elephant populations and the threats they face in these poorly understood areas. Interview-based occupancy analysis is a reliable and suitable method for a rapid assessment of forest elephant occupancy on a large scale, as a complement to, or the first stage in, a monitoring process
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