• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 338
  • 26
  • 16
  • 9
  • 5
  • 4
  • 3
  • 2
  • 1
  • Tagged with
  • 448
  • 448
  • 142
  • 72
  • 57
  • 53
  • 48
  • 35
  • 34
  • 25
  • 23
  • 23
  • 23
  • 22
  • 22
  • 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.
281

The Abundance and Behavioral Ecology of Cape Cod Gray Seals Under Predation Risk From White Sharks

Moxley, Jerry Hall January 2016 (has links)
<p>The ultimate goal of wildlife recovery is abundance growth of a species, though it must also involve the reestablishment of the species’ ecological role within ecosystems frequently modified by humans. Reestablishment and subsequent recovery may depend on the species’ degree of adaptive behavior as well as the duration of their functional absence and the extent of ecosystem alteration. In cases of long extirpations or extensive alteration, successful reestablishment may entail adjusting foraging behavior, targeting new prey species, and encountering unfamiliar predatory or competitive regimes. Recovering species must also increasingly tolerate heightened anthropogenic presence, particularly within densely inhabited coastal zones. In recent decades, gray seals (Halichoerus grypus) recovered from exploitation, depletion, and partial extirpation in the Northwest Atlantic. On Cape Cod, MA, USA, gray seals have reestablished growing breeding colonies and seasonally interact with migratory white sharks (Carcarodon carcharias). Though well-studied in portions of their range due to concerns over piscivorous impacts on valuable groundfish, there are broad knowledge gaps regarding their ecological role to US marine ecosystems. Furthermore, there are few studies that explicitly analyze gray seal behavior under direct risk of documented shark predation. </p><p> In this dissertation, I apply a behavioral and movement ecology approach to telemetry data to understand gray seal abundance and activity patterns along the coast of Cape Cod. This coastal focus complements extensive research documenting and describing offshore movement and foraging behavior and allows me to address questions about movement decisions and risk allocation. Using beach counts of seals visible in satellite imagery, I estimate the total regional abundance of gray seals using correction factors from haul out behavior and demonstrate a sizeable prey base of gray seals locally. Analyzing intra-annual space use patterns, I document small, concentrated home ranges utilizing nearshore habitats that rapidly expand with shifting activity budgets to target disperse offshore habitats following seasonal declines in white sharks. During the season of dense shark presence, seals conducted abbreviated nocturnal foraging trips structured temporally around divergent use of crepuscular periods. The timing of coastal behavior with different levels of twilight indicate risk allocation patterns with diel cycles of empirical white shark activity. The emergence of risk allocation to explain unique behavioral and spatial patterns observed in these gray seals points to the importance of the restored predator-prey dynamic in gray seal behavior along Cape Cod.</p> / Dissertation
282

The influence of fire and grazing on tallgrass prairie streams and herpetofauna

Larson, Danelle Marie January 1900 (has links)
Doctor of Philosophy / Division of Biology / Walter K. Dodds / Tallgrass prairie evolved with fire-grazer interactions. Fire and grazing are vital processes for maintaining grasslands and cattle production, and therefore will be continued as land management schemes. The effects of fire and grazers on prairie streams are understudied, but may significantly influence stream ecology. This dissertation examined how prescribed burning, bison grazing, and patch-burn grazing (by cattle) influence water quality, stream biota, and riparian amphibians and reptiles at Konza Prairie, Kansas, or Osage Prairie, Missouri. Using Global Positioning System, we monitored bison and cattle distribution throughout watersheds. The immediate effects of prescribed burning were examined at both Konza and Osage Prairies. The impacts of bison on water quality were determined by using a long-term dataset from Konza Prairie and compared watersheds with and without bison. Amphibian and reptile assemblages were monitored for two years at Osage, and assemblage data were analyzed using redundancy analysis, permuted analysis of variance, and occupancy modeling. A patch-burn grazing experiment occurred for 5 years at Osage (2 years pretreatment data and 3 years of treatments) and was analyzed using a before-after, control-impact design. Prescribed burning had minimal effects on water chemistry. At Konza Prairie, bison did not alter water quality likely because they spent negligible time (<5%) in streams. Contrarily, cattle at Osage Prairie significantly increased stream concentrations of total suspended solids, nutrients, Escherichia coli bacteria, algal biomass, and primary production. Unlike bison, cattle spent significant time (~21%) in streams if allowed access to riparian zones. In watersheds with cattle excluded from streams by riparian fencing, water quality contaminant concentrations increased significantly, but not to the magnitude of unfenced streams. Amphibian abundance and richness were not different among patch types; instead, they were restricted to specific basins. However, reptiles displayed preference for certain patch-types, and had the highest abundance and richness in watersheds with fire and grazing. These results have implications for natural resource management. Riparian fencing of cattle may be a useful practice in areas where water resource protection is the priority. However, overland flow may alter water quality in watersheds with grazers despite fencing. Land managers will need to define management objectives and accept trade-offs in water quality, amphibian and reptile habitat, and cattle production.
283

Distribution and Conservation of the Antillean Manatee in Hispaniola

Dominguez Tejo, Haydee Maria January 2016 (has links)
<p>Antillean manatees (Trichechus manatus manatus) were heavily hunted in the past throughout the Wider Caribbean Region (WCR), and are currently listed as endangered on the IUCN Red List of Threatened Species. In most WCR countries, including Haiti and the Dominican Republic, remaining manatee populations are believed to be small and declining, but current information is needed on their status, distribution, and local threats to the species.</p><p>To assess the past and current distribution and conservation status of the Antillean manatee in Hispaniola, I conducted a systematic review of documentary archives dating from the pre-Columbian era to 2013. I then surveyed more than 670 artisanal fishers from Haiti and the Dominican Republic in 2013-2014 using a standardized questionnaire. Finally, to identify important areas for manatees in the Dominican Republic, I developed a country-wide ensemble model of manatee distribution, and compared modeled hotspots with those identified by fishers.</p><p>Manatees were historically abundant in Hispaniola, but were hunted for their meat and became relatively rare by the end of the 19th century. The use of manatee body parts diversified with time to include their oil, skin, and bones. Traditional uses for folk medicine and handcrafts persist today in coastal communities in the Dominican Republic. Most threats to Antillean manatees in Hispaniola are anthropogenic in nature, and most mortality is caused by fisheries. I estimated a minimum island-wide annual mortality of approximately 20 animals. To understand the impact of this level of mortality, and to provide a baseline for measuring the success of future conservation actions, the Dominican Republic and Haiti should work together to obtain a reliable estimate of the current population size of manatees in Hispaniola.</p><p> </p><p>In Haiti, the survey of fishers showed a wider distribution range of the species than suggested by the documentary archive review: fishers reported recent manatee sightings in seven of nine coastal departments, and three manatee hotspot areas were identified in the north, central, and south coasts. Thus, the contracted manatee distribution range suggested by the documentary archive review likely reflects a lack of research in Haiti. Both the review and the interviews agreed that manatees no longer occupy freshwater habitats in the country. In general, more dedicated manatee studies are needed in Haiti, employing aerial, land, or boat surveys. </p><p>In the Dominican Republic, the documentary archive review and the survey of fishers showed that manatees still occur throughout the country, and occasionally occupy freshwater habitats. Monte Cristi province in the north coast, and Barahona province in the south coast, were identified as focal areas. Sighting reports of manatees decreased from Monte Cristi eastwards to the adjacent province in the Dominican Republic, and westwards into Haiti. Along the north coast of Haiti, the number of manatee sighting and capture reports decreased with increasing distance to Monte Cristi province. There was good agreement among the modeled manatee hotspots, hotspots identified by fishers, and hotspots identified during previous dedicated manatee studies. The concordance of these results suggests that the distribution and patterns of habitat use of manatees in the Dominican Republic have not changed dramatically in over 30 years, and that the remaining manatees exhibit some degree of site fidelity. The ensemble modeling approach used in the present study produced accurate and detailed maps of manatee distribution with minimum data requirements. This modeling strategy is replicable and readily transferable to other countries in the Caribbean or elsewhere with limited data on a species of interest.</p><p>The intrinsic value of manatees was stronger for artisanal fishers in the Dominican Republic than in Haiti, and most Dominican fishers showed a positive attitude towards manatee conservation. The Dominican Republic is an upper middle income country with a high Human Development Index. It possesses a legal framework that specifically protects manatees, and has a greater number of marine protected areas, more dedicated manatee studies, and more manatee education and awareness campaigns than Haiti. The constant presence of manatees in specific coastal segments of the Dominican Republic, the perceived decline in the number of manatee captures, and a more conservation-minded public, offer hope for manatee conservation, as non-consumptive uses of manatees become more popular. I recommend a series of conservation actions in the Dominican Republic, including: reducing risks to manatees from harmful fishing gear and watercraft at confirmed manatee hotspots; providing alternative economic alternatives for displaced fishers, and developing responsible ecotourism ventures for manatee watching; improving law enforcement to reduce fisheries-related manatee deaths, stop the illegal trade in manatee body parts, and better protect manatee habitat; and continuing education and awareness campaigns for coastal communities near manatee hotspots. </p><p>In contrast, most fishers in Haiti continue to value manatees as a source of food and income, and showed a generally negative attitude towards manatee conservation. Haiti is a low income country with a low Human Development Index. Only a single dedicated manatee study has been conducted in Haiti, and manatees are not officially protected. Positive initiatives for manatees in Haiti include: protected areas declared in 2013 and 2014 that enclose two of the manatee hotspots identified in the present study; and local organizations that are currently working on coastal and marine environmental issues, including research and education on marine mammals. Future conservation efforts for manatees in Haiti should focus on addressing poverty and providing viable economic alternatives for coastal communities. I recommend a community partnership approach for manatee conservation, paired with education and awareness campaigns to inform coastal communities about the conservation situation of manatees in Haiti, and to help change their perceived value. Haiti should also provide legal protection for manatees and their habitat.</p> / Dissertation
284

Desempenho de projetos de gestão ambiental pública: parcerias entre o Estado de São Paulo e organizações sem fins lucrativos / Performance of environmental management projects: partnerships between the State of São Paulo and not-for-profit organizations

Uehara, Thiago Hector Kanashiro 30 March 2010 (has links)
A coerência e a efetividade de iniciativas na área ambiental são centrais a projetos de gestão ambiental. Alguns projetos de gestão pública são desenvolvidos por meio de parceria entre Estado e organização sem fins lucrativos. Esta pesquisa tem por objetivo analisar características de organizações sem fins lucrativos parceiras do Estado e suas relações com o desempenho de projetos de gestão ambiental pública. A parceria entre Estado e organizações sem fins lucrativos se mostrou parcialmente colaborativa no cenário dos projetos estudados: o Estado planeja e controla as atividades de forma centralizada, restando às organizações sem fins lucrativos o papel de executoras com a função de intermediar Estado e comunidades rurais. Projetos de alto desempenho foram destacados segundo índice composto por indicadores de produtividade, de processo e de qualidade. As organizações executoras nem sempre declaram missão e são majoritariamente associadas à produção agropecuária ou às questões socioambientais e foram separadas em três grupos: as adhocráticas; as simples e burocráticas; e a divisionalizada. Organização executora de projeto de alta performance declara sua razão de existência, planeja pouco suas ações e tem comportamento formalizado. Destacam-se dois tipos organizacionais relacionados com alta performance de projetos deliberados pelo Estado: organização voltada à questão socioambiental que seja orgânica/ não-burocrática; e associação de produtores rurais que esteja sob amplo controle externo e que tenha processos de trabalho padronizados. / Coherence and effectiveness of initiatives in the environmental issues are central to environmental management projects. Some of them are developed through partnerships between State and not-for-profit organizations. This study aims to analyze the characteristics of not-for-profit organizations and its relations with project performance. In the context of the 15 projects reviewed, the partnership between State and not-for-profit organizations is partly collaborative: planning and controlling are directed by the State and the implementing role is assigned for the not-for-profit organizations. High-performance projects were highlighted due to an evaluation of indicators of productivity, process and quality. Implementing organizations do not always exhibit their mision statements and they are mostly associated to agricultural production or environmental issues. Organization that implements high-performance projects presents its reason for existence, do not plan too much and has a formalized behavior. In addition, two organizational types related to high-performance projects deliberated by the State are emphasized: organization devoted to socioenvironmental issues that is organic / non-bureaucratic ; and farmers association with standardized work processes under extensive external control.
285

Ecological correlates of the abundance of juvenile green sea turtles (Chelonia Mydas) on nearshore reefs in southeast Florida

Unknown Date (has links)
Juvenile green turtle (Chelonia mydas) abundance differs among nearshore reefs, but why some sites are preferred over others is unknown. My study had two objectives: to quantify differences in abundance over time (one year) and to determine what ecological factors were correlated with those differences. I conducted quarterly surveys on reefs in Palm Beach and Broward Counties and compared reef sites with respect to (i) water depth, (ii) algal abundance and composition, and (iii) changes in reef area (caused by sand covering) through time (11 years). Turtles were most abundant on shallow reefs exposed to high light levels that remained stable (uncovered by sand) for long periods of time. These reefs had the highest diversity of algal species, in part because cropping by the turtles prevented any one species from becoming dominant. My results suggest that both physical and biological factors make some reefs more attractive to turtles than others / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.
286

A Novel Interaction: The thin stripe hermit Crab, Clibanarius vittatus, kills the Florida crown conch, Melongena corona, for its shell

Unknown Date (has links)
The hermit crab Clibanarius vittatus kills Melongena corona solely to acquire a better fitting shell. This finding is contrary to previous studies, which found that hermit crabs of other species cannot kill gastropods or, in most instances, remove freshly dead gastropods from their shells. This interaction cannot be classified as predation because Melongena tissue was never consumed. Clibanarius killed Melongena only when by doing so they could trade up to a better fitting shell. It cannot be classified as competition because there is no opportunity for Melongena to gain from the interaction. Therefore the term “lethal eviction” is hereby proposed for this interaction. The ability to kill a gastropod to obtain a superior shell gives Clibanarius vittatus an evolutionary advantage over other hermit crab species. It is not known if the outcome of this interaction is widespread where both species occur or if it is confined to the study area. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection
287

Using Anthropogenic Parameters at Multiple Scales to Inform Conservation and Management of a Large Carnivore

Wynn-Grant, Rae Jackson January 2015 (has links)
Human influence on the environment is becoming increasingly pervasive across the globe, and can drastically impact ecological patterns and processes. For many terrestrial wildlife species, human influence can fragment critical habitat, increase mortality, and threaten habitat connectivity and ultimately the persistence of wildlife populations. This dissertation aims to use multiple conservation ecology methods and tools to test the impact of human influence on the population dynamics of a large carnivore in a human-dominated landscape. To assess the impact of human activity on carnivore ecology, a series of empirical studies were conducted on a small population of American black bear (Ursus americanus) in the Western Great Basin, USA. A long-term dataset including geographic locations of animal habitat choices as well as mortality locations were used in multiple statistical models that tested the response of black bears to human activity. These analyses were conducted at multiple spatial and temporal resolutions to reveal nuances potentially overlooked if analyses were limited to a single resolution. Individual studies, presented as dissertation chapters, examine the relationships between human activity and carnivore ecology. Collectively, the results of these studies find black bear ecology to be highly sensitive to the magnitude and spatial composition of human activity in the Lake Tahoe Basin, observable at both coarse and fine spatial resolutions. The results presented in this study on the influence of human activity on large carnivore population dynamics allow for a more thorough understanding of the various ways common conservation ecology methods and tools can be used to evaluate human-wildlife relationships.
288

Bushmeat hunting, retaliatory killing, habitat degradation and exotic species as threats to Fosa (Cryptoprocta ferox) conservation

Merson, Samuel David January 2017 (has links)
Large carnivores are in global decline, chiefly resultant of anthropogenic persecution, habitat reduction and disturbance. Fosas represent Madagascar's largest carnivore, occupying much of the island's forest. This thesis examines the threats of bushmeat hunting, retaliatory killing, habitat alteration and exotic species using sociological and remote-sensing methodologies. Habitat degradation was not associated with reduced fosa occupancy, indicating some resilience within large, contiguous forests. However, competition with exotic species (cats, dogs) was associated with reduced fosa occupancy and potential temporal shifts towards greater nocturnality. Poor households were more likely to consume protected species. Conversely, wealthier households consumed more fish and eel. This pattern is reflected in Malagasy reported taste preference to consume domesticated animals and certain legally hunted wild species. Protected areas were not associated with reduced protected species consumption. Fosas' predation was a major cause of rural poultry mortality. Predation was more likely to occur in deciduous forests, in the dry season, during the evening. Fosa predation, and lower education was associated with negative Malagasy attitudes. Wealthy households, and those that had experienced fosa predation were most likely to retaliatory kill a fosa. Strategies to safeguard fosas' long-term persistence should seek to improve domestic husbandry, build robust coops with the use of watchdogs, promote education, and reduce exotic species abundance.
289

Forecasting the Winners and Losers of a Riparian Herpetofauna in Response to Habitat Invasion and Xerification

January 2018 (has links)
abstract: Riparian systems in the arid southwest are heavily altered and, based on relative land-area, provision a disproportionately high number of native wildlife. Amphibians and reptiles are collectively the most threatened vertebrate taxa and, in the Sonoran Desert, are often reliant on riparian habitat. The link between amphibians and environmental water characteristics, as well as the association between lizards and habitat structure, make herpetofauna good organisms for which to examine the effects of environmental change. My objective was to relate capture rates of a fossorial anuran and lizard abundance to aspects of native, invaded, and shrub-encroached riparian habitats in order to forecast the potential winners and losers of riparian habitat xerification and invasion. I measured habitat and monitored herpetofauna at 18 sites near the confluence of the San Pedro River and Gila River in Pinal County, Arizona in 2016 and 2017. Sites were divided into three categories based on dominant tree genus; Populus-Salix, Prosopis, and Tamarix, which represented native riparia, xeric riparia, and invaded riparia, respectively. Habitat measurements indicated that sites varied significantly in structure, and that dominant tree species was a useful descriptor of habitat physiognomy. Results from herpetofauna trapping demonstrated that Scaphiopus couchii, a fossorial anuran, occupy Prosopis sites at a much higher rate than at Tamarix sites, which were almost completely avoided. S. couchii was also found to be closely tied to xero-riparian habitat components present at Prosopis sites and soil analyses indicate that aspects of soil moisture and texture play an important role in the partitioning of this species across altered riparian habitats. Lizard abundance was found to be significantly lower in Tamarix habitat, with the majority of captures attributed to the generalist whiptail Aspidoscelis tigris. Additionally, more than half of lizard species that were analyzed displayed a negative association to Tamarix habitat. Of the three habitat types considered, Populus-Salix supported the greatest abundance of lizards. Based on this study, the deleterious effects of xerfication on a riparian herpetofauna community may be lesser than those of Tamarix invasion. These two forms of riparian habitat shift often co-occur, with the ultimate cause being changes in hydrologic regime. This may imply that a bottom-up approach, wherein historic hydrology is restored to restore or maintain native habitats, to riverine management is appropriate for riparian herpetofauna conservation. / Dissertation/Thesis / Masters Thesis Applied Biological Sciences 2018
290

Effects of Climate and Water Use on the Ecology of Mountain Lakes and Rivers in the Western United States

Caldwell, Timothy J. 14 February 2019 (has links)
<p> Climate change and over-use of natural resources impacts ecosystems worldwide. Understanding physical impacts from climate and natural resource use on biological processes at multiple scales of spatial and ecological organization is needed to make useful predictions under global change scenarios. Mountain aquatic ecosystems are of particular concern because they are sensitive to climate change, represent hot spots of biodiversity, and they integrate atmospheric, terrestrial and aquatic processes into biological responses. The objective of this dissertation is to quantify physical impacts and biological responses of climate and water use on mountain aquatic ecosystems in the Western United States. In Chapter 1, I developed a data set of ice break-up dates using remote sensing techniques for mountain lakes across the Sierra and Cascade Mountain Ranges coupled with downscaled climate data to quantify drivers of lake ice phenology. I developed a predictive linear mixed effects model and used and ensemble of 15 global climate models to project changes in lake ice break-up dates through the 21<sup>st</sup> century. The results suggest that low snowpack and increased energy fluxes associated with elevated air temperatures drive earlier ice break-up dates. Projections of ice break-up show that ice break-up will be 61 &plusmn; 5 days if greenhouse gas emissions are not reduced. In Chapter 2, I analyzed specific ecological responses to earlier ice break-up dates in Castle Lake, California (a natural, sub-alpine lake). I predicted that consumer (Brook Trout; <i>Salvelinus fontinalis</i>) energetics and habitat use would be regulated by either climate driven water temperature or variation in food availability. The data suggest that earlier ice break-up results in a longer duration of surface water temperatures > 15 &deg;C, coupled with decreased and increased food production in the pelagic and littoral zones, respectively. Isotopic and telemetry data showed that consumer resources and habitat use were driven by water temperature and were independent of food availability. In early ice break-up years, consumers grew less because they were thermally excluded from productive littoral zones when water temperatures were warmer for longer periods of time relative to late ice break-up years. In Chapter 3, I demonstrate that decreased streamflow in mountain rivers can reduce abundance and size structure of food supply to drift foraging Rainbow Trout <i>(Onchorhynchus mykiss)</i>. In response to changes in streamflow and food availability, trout abandoned their energetically profitable drift foraging strategy and actively searched for prey. The shift in foraging behavior resulted in negative bioenergetic efficiencies in flow impaired sites. Taken collectively this research demonstrates that both predictable and unpredictable consequences of physical change drive biological responses across spatial gradients, ecosystem types, and levels of ecological organization.</p><p>

Page generated in 0.1447 seconds