• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 26
  • 6
  • 5
  • 3
  • 3
  • 2
  • Tagged with
  • 56
  • 11
  • 9
  • 9
  • 9
  • 8
  • 8
  • 8
  • 6
  • 6
  • 6
  • 6
  • 6
  • 5
  • 5
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

The relationship between nasal turbinate structure and the ecological attributes of ungulates

Kietzmann, Michelle Ann January 2010 (has links)
The nasal turbinates of ungulates are complex bony scrolls within the nasal cavity. These intricate bony plates, covered by moist epithelium, provide a large surface area that facilitates a countercurrent exchange of both water and heat between turbinal lining and respired air. Given their functional importance, maxilloturbinate size and structural dimensions may vary among species of different body sizes, activity levels and from different habitats, and may also serve as a predictor of the ability of the species to cope with high temperatures or limiting water resources. This is the first study to measure nasal turbinate surface area in ungulates using high-resolution computed tomography (CT) scanning. Heads of eleven South African bovid species and one European bovid species were successfully scanned and surface area measurements made using stereological techniques. These species included Cape grysbok, springbuck, bushbuck, blesbok, impala, mountain reedbuck, fallow deer, kudu, nyala, gemsbok and blue wildebeest; and represent species of different body sizes, from a range of habitats and with different water dependencies and predator avoidance strategies. The total maxilloturbinate surface area increased with body size for all study species. The surface areas of the nasal turbinates varied rostrocaudally, with the highest surface area occurring approximately midway along the length of the maxilloturbinate bones. The Cape grysbok stood out as having a nasal turbinate surface area of 12.77 cm2/kg, which was lower than the observed trend, the reason for this not being clear from these data. Phylogenetic independent analyses showed that log body mass and water dependence had a significant effect on nasal turbinate surface area, with habitat, distributional range and anti-predator behaviour having no effect. Subsequent phylogenetic species comparisons showed that structural variations in nasal turbinate surface area were phylogeny based due to the close genetic relatedness of the study species, and not associated with any environmental factors. The environmentally linked results for water dependency need further investigation in future studies of larger sample sizes and a broader range of species. Changes in climatic conditions may impact on a species‟ activity patterns, with individuals being forced to make behavioural modifications rather than physiological or anatomical adjustments. However, there is no clear evidence to indicate large differences in nasal turbinate surface area in relation to water dependence. This subsequently rules out the use of nasal turbinate surface area as a predictor to which and how ungulate species will respond to increasing global temperatures.
12

The value of using landsat 8 indices to describe large herbivore distribution

Mordecai, Kim Morag 19 September 2016 (has links)
A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfillment of the requirements for the degree of Masters in Science. / Satellite imagery and remote sensing techniques provide a way to collect data over large temporal and spatial scales, and build indices that gauge ecological variables. These indices can explain the distribution of animals in their environment. In this study I compare the ability of various indices derived from Landsat 8, to reliably predict locations of different large herbivore species across diverse habitats. The study was undertaken in the Kgaswane Mountain Reserve, North West Province, South Africa. Daily locations of two herds of sable antelope (Hippotragus niger) and one herd of eland (Tragelaphus oryx) were used. One sable antelope herd (vlei herd) occupied a grassland plateau with a wetland and the other sable antelope herd (woodland herd), shared the wooded area at the base of the mountains with the eland herd. I described vegetation communities, burnt areas, geology and soil templates at animal locations during foraging bouts in the dry season; coinciding with the times of the Landsat images. The overall aim of this study was to see whether an index or a combination of indices could better describe animal locations than the normally used NDVI. I calculated a number of indices, and compared their predictive ability to define areas used by the study animals. Specifically, I compared the Normalised Difference Vegetation Index (NDVI) to Soil Adjusted Vegetation Index (SAVI), Visible Atmospherically Resistant Index (VARIgreen), Green Atmospherically Resistant Index (GARI), Normalised Difference Water Index (NDWI), a proxy for soil moisture; and mineral composite indices assessing clay minerals, ferrous minerals and iron oxide. I chose these indices as they describe the basic characteristics of an ecologically functioning unit. The locations of one of the sable antelope herds, located in grassland areas underlined by quartzite, were best described by NDVI, SAVI and VARIgreen. The locations of the other sable antelope herd, occurring in an open wooded area with shallow sandy soils on norite and quartzite, were best described by clay minerals and GARI. Eland locations, found in woodland areas characterised by deep norite soils, were best described by a combination of iron oxide, NDVI and SAVI. Therefore, NDVI proved to be an adequate indicator in open grassland areas, where it could be interchanged with SAVI, and improved by VARIgreen. In closed woodlands NDVI, SAVI and NDWI could all be used to describe browser locations. NDVI was not a suitable index when it came to describe locations of a grazer in a woodland/grassland matrix. However, it is important to keep in mind that my results pertain only to one dry season and two herbivore species, and therefore further studies would be needed to be able to generalise the results further. / MT2016
13

Ungulate browsing as an ecosystem process browser-plant-soil interactions in a southern African savanna /

Fornara, Dario Arturo. January 2005 (has links)
Thesis (Ph. D.)--University of Pretoria, 2005. / Title from PDF t.p. (viewed Mar. 27, 2006). Includes bibliographical references.
14

African wild dog (Lycaon pictus) area utilization in the northern Tuli game reserve, Botswana.

Van Wyk, Dewald. January 2013 (has links)
M. Tech. Nature Conservation / The influence of predation on ungulates is most commonly measured through the direct lethal effects of predators. However, indirect effects of predation risk may alter prey behaviour and survival. The introduction of a pack of African wild dogs (Lycaon pictus) into the Northern Tuli Game Reserve, Botswana, allowed various indirect responses of ungulates to predation risk to be investigated. The study focused on predation pressure and its effects on ungulate activities during the denning period of the wild dogs, and on how the distribution and density of prey and lions influenced wild dog movement patterns in both the denning and non-denning period.
15

Paleobiology of a Large Mammal Community From the Late Pleistocene of Sonora, Mexico

Short, Rachel A., Emmert, Laura G., Famoso, Nicholas A., Martin, Jeff M., Mead, Jim I., Swift, Sandy L., Baez, Arturo 01 July 2021 (has links)
A paleontological deposit near San Clemente de Térapa represents one of the very few Rancholabrean North American Land Mammal Age sites within Sonora, Mexico. During that time, grasslands were common, and the climate included cooler and drier summers and wetter winters than currently experienced in northern Mexico. Here, we demonstrate restructuring in the mammalian community associated with environmental change over the past 40,000 years at Térapa. The fossil community has a similar number of carnivores and herbivores whereas the modern community consists mostly of carnivores. There was also a 97% decrease in mean body size (from 289 kg to 9 kg) because of the loss of megafauna. We further provide an updated review of ungulates and carnivores, recognizing two distinct morphotypes of Equus, including E. scotti and a slighter species; as well as Platygonus compressus; Camelops hesternus; Canis dirus; and Lynx rufus; and the first regional records of Palaeolama mirifica, Procyon lotor, and Smilodon cf. S. fatalis. The Térapa mammals presented here provide a more comprehensive understanding of the faunal community restructuring that occurred in northern Mexico from the late Pleistocene to present day, indicating further potential biodiversity loss with continued warming and drying of the region.
16

Investigating the Influence of Available Drinking Water on Wildlife in Utah's West Desert

Finlayson, Danielle K. 09 December 2021 (has links)
The availability of water is a limiting resource for many wildlife species in arid and semi- arid environments. Free water is essential for critical life stages for numerous species, including migration, reproduction, survival, and habitat selection. Riparian areas in the desert occur relatively infrequently, but support a disproportionally large percentage of plant and wildlife species found in arid environments. Our study covered two aspects of water use in the west desert of Utah. The first was assessing the impacts of nonnative ungulates (specifically feral horses and cattle) on natural springs, and how they influenced water quality, vegetation, and wildlife diversity at those springs. We found that these ungulates reduced plant cover and plant species richness at our sites. Additionally, we found that the number of plant species positively correlated with wildlife diversity. This indicates that further management of these nonnative ungulates may be warranted. In our second chapter we investigate how Golden Eagles (Aquila chrysaetos) use water by quantifying seasonal use, behavior, and testing a hypothesis that a ‘runway’ with drop in elevation is needed for eagles to have a quick exit. We found that eagle use of water resources was strongly concentrated in the summer months during the hottest temperatures. Adult birds used water features more often than younger birds. The most common behavior exhibited at water features was drinking, followed by bathing and preening. We found that there was a positive relationship between the number of visits and the maximum slope at each site, supporting the idea that the ‘runway’ is not required but is preferred at water sources. Overall, our results indicated that Golden Eagles use water regularly in arid environments, particularly during summer months. This research provides insight into how species are using desert riparian areas and how these species and habitats should be managed in future decades.
17

A study of sex/age ratios in wild ungulate populations : an approach to designing an appropriate sampling strategy for estimating the structure of wild ungulate populations on Rooipoort Nature Reserve

Laubscher, Sarah-Jane 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: This thesis investigates the population structure of a number of ungulate species occurring within Rooipoort private reserve. Specifically the study serves to make estimates of the ratio of males to females and calves to cows within each species population under observation, based on the data collected. Data were also analysed to ascertain the distribution patterns of the species in question, in relation to vegetation type and habitat. Distribution data were additionally compared to distribution data collected at an earlier period on Rooipoort, to determine whether any change has occurred in distribution patterns of the ungulates concerned. Through analysis of both sex/age data and distributional data, one of the main objectives of the study was to determine the most appropriate time of the year, length of time and managment costs involved to undertake sex/age counts on Rooipoort. Results of the study were also compared to existing population models of ungulates on the reserve. Results obtained from data concluded that a single monthly sex/age count or, in some cases, even three consecutive monthly counts, to determine age ratios, would be insufficient to deliver a reliable estimate of population structure. A number of counts would have to be carried out throughout the year in order to make reliable estimates. Distribution data revealed that all habitat/vegetation types on Rooipoort would have to be covered in order to effectively sample all of the species in question. / AFRIKAANSE OPSOMMING: Gegewens is ook ontleed om die verspreidingspatrone van hoefdiersoorte te bepaal met betrekking tot plantegroeitipe en habitat. Die verspreidingsdata is ook vergelyk met vorige ..studies wat op Rooipoort gedoen is om te. bepaal. of enige. veranderings in die verpreidingspatrone van die hoefdiere onder bespreking plaasgevind het. Een van die hoof doelwitte van die studie was om.. deur ontleding. van beide die geslags/ouderdom data en die verspreidingsdata, die mees geskikte tye van die jaar, die tydsduur en bestuurskoste te bepaal, om geslags/ouderdomstellings op Rooipoort uit te voer. Resultate van die studie is ook met vertroude populasiemodelle op die reservaat vergelyk. Die dataontledings het aangeduidat 'n enkele maandlikse geslags/ouderdoms telling, of, In sekere gevalle, selfs drie agtereenvolgende maandlikse tellings, om ouderdomsverhoudings te bepaal, nie voldoende sal wees om 'n vertroubare beraming van die bevolkings struktuur te maak. n' Aantal tellings moet gedurende die yaar uitgevoer word om vertroubare beramings te kan doen. Verspreidingsdata het bevestig dat alle habitate en plantegroeitipes op Rooipoort bemonster moet word om alle spesie effektief te bemonster.
18

Elephant versus other browsers' long-term influences on savanna woodland dynamics : synergistic influences of elephant and other large mammalian herbivores on the structure and composition of woody plant communities in Hluhluwe-iMfolozi Park, South Africa

O'Kane, Christopher Anthony John January 2012 (has links)
A crucial question in the debate about reintroducing elephant culling is whether the long-term effects of elephants and mesobrowsers on woodlands are similar. Sufficiently high biomass-densities of mesobrowsers may, following reduction or removal of elephants, continue to heavily impact earlier life-history stages of a similar suite of woody plants that elephant impacted, preventing these species from maturing. Thus a similar end-point for woodland structure and composition is achieved. No study exists in the literature where woody plant and habitat utilisation of the savanna browser guild has been determined in the same locality over the same period. A review of 49 years of literature implied that the two groups impact the same core woody-species in the same habitats. Dietary and habitat utilisation of guild members was determined in Hluhluwe-iMfolozi Park, South Africa. A small suite (n = 8) of woody species formed the core diet of all guild members. Herbivores’ densities were determined using a novel GIS approach; all members of the guild showed extensive overlap in habitat use. GPS collars and a GIS were then used to detect zones of different density of impala in the landscape, thus defining, for the first time, a natural fine-grain browsing gradient. Densities of woody seedlings were significantly less (average 48% reduction) in areas of high versus low impala density. A simple browse-browser model, incorporating, in a novel approach, functional groups of plant species, was parameterised from these results and an extensive review of the literature. Outputs suggest that over the long-term (100 years), impala will have a similar impact on woodland structure as elephant. An apparently strong synergistic effect between impala and elephant impact, suggests that reduction or removal of either impala or elephant will radically reduce long-term destruction of woodlands. In smaller or medium sized reserves, where control of mesobrowser populations is practical, profitable and more acceptable than elephant culling, these findings imply a re-direction of management efforts. Management should consider the biomass-density of both groups, rather than just focus on the system’s perceived ‘keystone’ species. Such principles may also apply to temperate and other systems.
19

The relative importance of beavers (Castor fiber) and browsers on the recruitment of broad-leaved trees in riparian areas

Karlsson, Matilda January 2019 (has links)
Managed forest landscapes in Sweden are dominated by boreal coniferous forest and are deficient in broad-leaved trees. Both beavers (Castor fiber) and ungulate browsers prefer broad-leaved trees to conifers, and the interaction between multiple herbivores may have a considerable impact on the recruitment of deciduous trees in riparian areas. To evaluate the relative importance of beavers and browsers on tree recruitment, I conducted an inventory of broad-leaved tree species at five beaver sites in Färnebofjärden National Park, Sweden. At each site, five transects were established perpendicular to the shoreline in the riparian zone, resulting in a grid of 35 sample plots at each beaver site. Foraging activity of both beavers and browsers (e.g. ungulates) was concentrated to a narrow band in the riparian zone and there was a decrease in the proportion of beaver-cut and browsed trees further away from the shoreline. Beavers preferred birch (Betula spp.) and grey willow (Salix cinerea) while browsers preferred oak (Quercus robur). Beavers targeted larger trees while browsers targeted seedlings <1 cm in diameter. Old-growth trees of high conservation value, such as aspen (Populus tremula) and birch, are at risk to be cut by beaver, yet long-term protection of broad-leaved stands requires a shift in focus towards strategies that enhance tree recruitment by considering and mitigating pressure from multiple herbivores. / Svenska skogslandskap domineras av boreal barrskog med en brist på lövträd. Både bäver (Castor fiber) och betande klövvilt föredrar lövträd framför barrträd, och interaktionen mellan dessa herbivorer kan ha en betydande påverkan på föryngring av lövträd i strandnära skogar. För att utvärdera den relativa betydelsen av bävrar och betare på trädföryngring så genomförde jag en inventering av lövträdsarter och betestryck vid fem bäverlokaler i Färnebofjärden Nationalpark, Sverige. Vid varje bäverlokal lades fem transekter i rät vinkel mot strandkanten i den strandnära zonen, med provrutor var femte meter längs varje transekt, vilket resulterade i ett nätverk av 35 provrutor vid varje lokal. Både bävrars och betares (dvs. klövvilts) födosökande var begränsat till ett smalt band längs strandkanten, och andelen bävergnagda och betade trädstammar minskade med ökat avstånd från strandkanten. Bäver föredrog björk och gråvide medan betare föredrog ek. Bäver föredrog större träd medan betare föredrog groddplantor <1 cm i diameter. Gamla lövträd som är viktiga att bevara, såsom asp och björk, hotas av bäveraktivitet, men långsiktigt bevarande av lövträdsbestånd kräver ett fokus på strategier som främjar trädföryngring, bland annat genom att beakta och begränsa den sammantagna påverkan av olika herbivorers betning.
20

Parasitisme et structuration génétique et spatiale : exemple chez le mouflon méditerranéen, Ovis gmelini musimon x Ovis sp / Parasitism and spatial genetic structure : Example of the Mediteranean Mouflon, Ovis gmelini musimon x Ovis sp.

Portanier, Elodie 29 November 2018 (has links)
En utilisant comme cas d’étude le mouflon Méditerranéen (Ovis gmelini musimon × Ovis sp.), les objectifs de cette thèse étaient de mieux comprendre comment sont liés diversité génétique, comportement des individus, flux de gènes et dynamique parasitaire. Au travers d’approches de génétique des populations et de génétique du paysage, nous avons pu mettre en évidence que la structure génétique spatiale de la population étudiée était impactée par son histoire d’introduction, sa structure socio-spatiale et le paysage dans lequel elle évolue. Etant donné l’impact de ces divers éléments sur les flux de gènes des mouflons, nous nous attendions à ce qu’ils déterminent également les flux de parasites dans la population. Nos résultats ont, au contraire, révélé que les parasites circulent mieux que les gènes de mouflons dans la population. Enfin, nous avons montré que les capacités de résistance des hôtes face à leurs parasites dépendaient de la diversité génétique neutre et adaptative, notamment de l’hétérozygotie d’un gène lié à l’immunité. Les résultats de ce travail décrivent avec précision la distribution de la variabilité génétique et son lien avec les risques sanitaires dans la population d’étude, apportant ainsi des informations cruciales pour la mise en place de stratégies de gestion et de conservation des populations de mouflons dans le contexte actuel de changements globaux et de réémergences de maladies. / Using as a case study the Mediterranean mouflon (Ovis gmelini musimon × Ovis sp.), we aimed at better understanding how are linked genetic diversity, individual behaviour, gene flows and parasitic dynamic. Using population and landscape genetics approaches, we showed that the spatial genetic structure of the studied population was determined by its introduction history, its socio-spatial structure and the landscape in which it evolves. Given the impact of these elements on mouflon gene flow, we expected them to also determine parasite transmission in the population. Our results nevertheless evidenced that parasite are better dispersed than mouflon genes. Finally, we showed that host resistance to parasites depends on neutral and adaptive genetic diversity, and more specifically on heterozygosity at a immunity-linked locus. Our results precisely describe genetic variability spatial distribution and its link with sanitary risks in the studied population, bringing crucial information for wild sheep population management and conservation in the current context of global changes and disease reemergence.

Page generated in 0.1515 seconds