Tesi sul tema "Predators"
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1
Garza, Mark Isaac. "Predator induced defenses in prey with diverse predators". Texas A&M University, 2005. http://hdl.handle.net/1969.1/3309.
Testo completoAbstract (sommario):
Phenotypic plasticity is an environmentally based change in phenotype and can be
adaptive. Often, the change in an organism's phenotype is induced by the presence of a
predator and serves as a defense against that predator. Defensive phenotypes are induced
in freshwater physid snails in response to both crayfish and molluscivorous fish.
Alternative morphologies are produced depending on which of these two predators snails
are raised with, thus protecting them from each of these predators' unique mode of
predation. Snails and other mollusks have been shown to produce thicker, differently
shaped shells when found with predators relative to those found without predators. This
production of thicker, differently shaped shells offers better protection against predators
because of increased predator resistance.
The first study in this thesis explores costs and limits to plasticity using the snailfish-
crayfish system. I exposed juvenile physid snails (using a family structure) to either
early or late shifts in predation regimes to assess whether developmental flexibility is
equally possible early and late in development. Physid snails were observed to produce
alternative defensive morphologies when raised in the presence of each of the two
predators. All families responded similarly to the environment in which they were raised.
Morphology was found to be heritable, but plasticity itself was not heritable. Morphology was found to become less flexible as snails progressed along their respective
developmental pathways.
In the second study, I raised physid snails with and without shell-crushing sunfish
and examined the differences in shell thickness, shell mass, shell size and shell
microstructural properties between the two treatment groups. Shells of snails raised with
predators were found to be larger, thicker and more massive than those raised without
predators, but differences in microstructure were found to be insignificant. I conclude that
the observed shell thickening is accomplished by the snails' depositing more of the same
material into their shells and not by producing a more complex shell composition.
2
Lourenço, Rui Nascimento Fazenda. "Predatory interactions among vertebrate top predators superpredation and intraguild predation by large raptors". Doctoral thesis, Universidade de Évora, 2011. http://hdl.handle.net/10174/14789.
Testo completoAbstract (sommario):
Nesta tese estudaram-se as interacções predatórias entre vertebrados predadores de topo
(predação intraguilda e superpredação), utilizando quatro aves de rapina de grande porte como
modelos de superpredadores: Bufo-real, Açor, Águia-real, e Águia de Bonelli. A superpredação em
aves de rapina é um fenómeno abrangente, que pode variar entre espécies, e mais frequente em
paisagens mais humanizadas. Os meso-predadores não são recursos energeticamente relevantes para
as aves de rapina, e o seu consumo está associado à diversificação da dieta resultante da diminuição
das presas habituais. A eliminação de competidores e potenciais predadores são outros factores que
podem aumentar a frequência da superpredação. O aumento da percentagem de meso-predadores na
dieta está associado a menor sucesso reprodutor e maiores níveis de acumulação de mercúrio nas
aves de rapina. O risco de predação pode levar um meso-predador (Coruja-do-mato) a diminuir a
sua actividade vocal de modo a estar menos exposto ao predador intraguilda; ABSTRACT: This thesis analyses predatory interactions among vertebrate top predadores (intraguild
predation and superpredation), using four large raptors as superpredator models: eagle owl,
goshawk, golden eagle and Bonelli's eagle. Superpredation in raptors is a widespread phenomenon,
that can vary between species, and that is more frequent in human-altered landscapes.
Mesopredators are not energetically relevant resources for raptors, and their consumption is related
to diet diversification as a result of the decline of staple prey. Competitor and predator removal are
additional factors that can cause an increase in superpredation rates. The increase of mesopredators
in the diet of raptors is associated to lower breeding success and higher levels of mercury
contamination. Predation risk can drive a mesopredator (tawny owl) to reduce its vocal activity in
order to be less exposed to its intraguild predator.
3
Vankeuren, Jody L. "Parasites Predators and Symbionts". Kent State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=kent1619475426952694.
Testo completo
4
Howe, Jeff. ""Predators" a short story collection". Thesis, Boston University, 2012. https://hdl.handle.net/2144/32025.
Testo completoAbstract (sommario):
Thesis (M.F.A.)--Boston University. Please note: creative writing theses are permanently embargoed in OpenBU. No public access is forecasted for these. To request private access, please click on the locked Download file link and fill out the appropriate web form.2031-01-02
5
Sitvarin, Michael Ian. "Behavioral and ecological consequences of multiple intraguild predators and connections between predators, prey, and ecosystem function". Miami University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=miami1408538928.
Testo completo
6
Lannsjö, Fredrik, Lionel Nurweze e Kristina Sörensen. "Modeling the Dynamics of Cooperative Predators". Thesis, KTH, Optimeringslära och systemteori, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103624.
Testo completoAbstract (sommario):
The focus of this thesis is the modeling of cooperative predators hunting ocks of animals. The modeling is based on biological studies of the behavior of speci c predators and their preys, lions and zebras for this case. General rules are established in order to model the overall hunting and escape strategies, with a focus on the former. The dynamics of the predator during the hunt are modeled using the unicycle model applied locally, i.e., applied to each agent. The cooperation is taken into account by considering the system as a multi-agent system. Subsequently, a computer simulation based on the mathematical models is constructed and numerous simulations performed. The results from the simulations are then compared to biological studies in order to assess the validity of the model. Keywords: Multi-agent, unicycle model, mathematical modeling, cooperative predator dynamics, bio-mimicryHuvudsyftet med den har uppsatsen ar att modellera samarbetande rovdjur i jakten efter bytesdjur. Modellen baseras pa biologiska studier av sarskilda rovdjur och deras bytesdjur, mer speci kt, lejon och zebror. Baserat pa dessa fakta skapas generella regler for att kunna beskriva beteenden vid jakt och ykt, med fokus pa det forstnamnda. Systemet behandlas som ett multi-agent system darfor och generaliseras sedan systemet ar ett multi-agent system och dynamiken hos det enskilda rovdjuret beskrivs med hjalp av en unicycle model som appliceras lokalt. Vidare gors en datorsimulering baserad pa denna matematiska model. Resultaten fran simuleringarna jamfors sedan med biologiska studier, for att utvardera modellens giltighet. Nyckelord: Multi-agent, unicycle model, matematisk modellering, bio-mimicry
7
Jones, Esther Lane. "Spatial ecology of marine top predators". Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/12278.
Testo completoAbstract (sommario):
Species distribution maps can provide important information to focus conservation efforts and enable spatial management of human activities. Two sympatric marine predators, grey seals (Halichoerus grypus) and harbour seals (Phoca vitulina), have overlapping ranges but contrasting population dynamics around the UK; whilst grey seals have generally increased, harbour seals have shown significant regional declines. A robust analytical methodology was developed to produce maps of grey and harbour seal usage estimates with corresponding uncertainty, and scales of spatial partitioning between the species were found. Throughout their range, both grey and harbour seals spend the majority of their time within 50 km of the coast. The scalability of the analytical approach was enhanced and environmental information to enable spatial predictions was included. The resultant maps have been applied to inform consent and licensing of marine renewable developments of wind farms and tidal turbines. For harbour seals around Orkney, northern Scotland, distance from haul out, proportion of sand in seabed sediment, and annual mean power were important predictors of space-use. Utilising seal usage maps, a framework was produced to allow shipping noise, an important marine anthropogenic stressor, to be explicitly incorporated into spatial planning. Potentially sensitive areas were identified through quantifying risk of exposure of shipping traffic to marine species. Individual noise exposure was predicted with associated uncertainty in an area with varying rates of co-occurrence. Across the UK, spatial overlap was highest within 50 km of the coast, close to seal haul outs. Areas identified with high risk of exposure included 11 Special Areas of Conservation (from a possible 25). Risk to harbour seal populations was highest, affecting half of all SACs associated with the species. For 20 of 28 animals in the acoustic exposure study, 95% CI for M-weighted cumulative Sound Exposure Levels had upper bounds above levels known to induce Temporary Threshold Shift. Predictions of broadband received sound pressure levels were underestimated on average by 0.7 dB re 1μPa (± 3.3). An analytical methodology was derived to allow ecological maps to be quantitatively compared. The Structural Similarity (SSIM) index was enhanced to incorporate uncertainty from underlying spatial models, and a software algorithm was developed to correct for internal edge effects so that loss of spatial information from the map comparison was limited. The application of the approach was demonstrated using a case study of sperm whales (Physeter macrocephalus, Linneaus 1758) in the Mediterranean Sea to identify areas where local-scale differences in space-use between groups and singleton whales occurred. SSIM is applicable to a broad range of spatial ecological data, providing a novel tool for map comparison.
8
Wilson, Rory Paul. "Breeding Jackass Penguins as pelagic predators". Doctoral thesis, University of Cape Town, 1986. http://hdl.handle.net/11427/17653.
Testo completoAbstract (sommario):
Bibliography: pages 187-191.The foraging of breeding Jackass Penguins Spheniscus demersus was studied in and around southwestern Cape Province, Saldanha Bay (33⁰ S, 18⁰ E), South Africa. Penguins are difficult to observe at sea. Hence, I devised a number of new techniques for studying the foraging behaviour of Jackass Penguins at sea. I built electronic and autoradiographic remote-sensing devices to measure swimming speed, distance travelled and time spent at each depth by foraging Jackass Penguins. Penguin swimming speed was reduced in proportion to the cross-sectional area of the devices, and results derived from birds wearing the devices had to be interpreted accordingly. Penguins do not regurgitate their stomach contents when handled, so I constructed a wet-offloading stomach pump which extracted 100% of the stomach contents. Using this pump, I determined that the rate of digestion of fish and squid by Jackass Penguins differed. Care is needed in diet interpretations where both fish and squid are major food items.
9
Ddumba, Hassan. "Repulsive-attractive models for the impact of two predators on prey species varying in anti-predator response". Thesis, Nelson Mandela Metropolitan University, 2011. http://hdl.handle.net/10948/d1010995.
Testo completoAbstract (sommario):
This study considers the dynamical interaction of two predatory carnivores (Lions (Panthera leo) and Spotted Hyaenas (Crocuta crocuta)) and three of their common prey (Buffalo (Syncerus caffer), Warthog (Phacochoerus africanus) and Kudu (Tragelaphus strepsiceros)). The dependence on spatial structure of species’ interaction stimulated the author to formulate reaction-diffusion models to explain the dynamics of predator-prey relationships in ecology. These models were used to predict and explain the effect of threshold populations, predator additional food and prey refuge on the general species’ dynamics. Vital parameters that model additional food to predators, prey refuge and population thresholds were given due attention in the analyses. The stability of a predator-prey model for an ecosystem faced with a prey out-flux which is analogous to and modelled as an Allee effect was investigated. The results highlight the bounds for the conversion efficiency of prey biomass to predator biomass (fertility gain) for which stability of the three species ecosystem model can be attained. Global stability analysis results showed that the prey (warthog) population density should exceed the sum of its carrying capacity and threshold value minus its equilibrium value i.e., W >(Kw + $) −W . This result shows that the warthog’s equilibrium population density is bounded above by population thresholds, i.e., W < (Kw+$). Besides showing the occurrence under parameter space of the so-called paradox of enrichment, early indicators of chaos can also be deduced. In addition, numerical results revealed stable oscillatory behaviour and stable spirals of the species as predator fertility rate, mortality rate and prey threshold were varied. The stabilising effect of prey refuge due to variations in predator fertility and proportion of prey in the refuge was studied. Formulation and analysis of a robust mathematical model for two predators having an overlapping dietary niche were also done. The Beddington-DeAngelis functional and numerical responses which are relevant in addressing the Principle of Competitive Exclusion as species interact were incorporated in the model. The stabilizing effect of additional food in relation to the relative diffusivity D, and wave number k, was investigated. Stability, dissipativity, permanence, persistence and periodicity of the model were studied using the routine and limit cycle perturbation methods. The periodic solutions (b 1 and b 3), which influence the dispersal rate (') of the interacting species, have been shown to be controlled by the wave number. For stability, and in order to overcome predator natural mortality, the nutritional value of predator additional food has been shown to be of high quality that can enhance predator fertility gain. The threshold relationships between various ecosystem parameters and the carrying capacity of the game park for the prey species were also deduced to ensure ecosystem persistence. Besides revealing irregular periodic travelling wave behaviour due to predator interference, numerical results also show oscillatory temporal dynamics resulting from additional food supplements combined with high predation rates.
10
Cox, Martin James. "Acoustic and ecological investigations into predator-prey interactions between Antarctic krill (Euphausia superba) and seal and bird predators". Thesis, St Andrews, 2008. http://hdl.handle.net/10023/579.
Testo completo
11
Madeira, Nogueira Filipe. "Movement of predators in arable crop systems". Doctoral thesis, Universitat de Lleida, 2014. http://hdl.handle.net/10803/285265.
Testo completoAbstract (sommario):
L`abundància i dispersió d`O. majusculus no va ser diferent entre parcel-les de panís amb moderadament alta o baixa densitat de males herbes. Els caràbids, C. fuscipes, P. rufipes, P. cupreus i Metallina sp. i l`antocòrid O. majusculus presenten moviment bidireccional entre cultius adjacents de alfals i panís durant l'estació. En contrast, C. septempunctata només es va moure des de l`alfals cap al panís. Els individus d'O. majusculus i C. septempunctata que van colonitzar el panís a l'estadi vegetatiu provenien de l`alfals, indicant que l`alfals va ser la font d'aquests depredadors. No obstant, en el període reproductiu, el panís va actuar com una font de C. fuscipes, P. rufipes, P. cupreus, Metallina sp. i O. majusculus cap a l`alfals, principalment després de dall. El moviment de caràbids, estafilínids i aranyes va ser més intens des dels cereals d'hivern cap als hàbitats semi naturals que des dels prats cap als hàbitats semi naturals, indicant que l'hàbitat adjacent modela el moviment dels depredadors cap als hàbitats semi naturals.La abundancia y dispersión de O. majusculus no fué diferente entre parcelas de maíz con moderada alta o baja densidad de las malas hierbas. Los carábidos, C. fuscipes, P. rufipes, P. cupreus y Metallina sp. y el anthocorido O. majusculus presentan movimiento bidireccional entre cultivos adyacentes de alfalfa y maíz durante la estación. En contraste, C. septempunctata sólo se movió desde la alfalfa hacia al maíz. Los individuos de O. majusculus y C. septempunctata que colonizaron el maíz en el estadio vegetativo provinieron de la alfalfa, indicando que la alfalfa actúo como fuente de estos depredadores. Sin embargo, en el período reproductivo, el maíz actuó como una fuente de C. fuscipes, P. rufipes, P. cupreus, Metallina sp. y O. majusculus hacia la alfalfa, principalmente después de corte. El movimiento de carábidos, estafilínidos y arañas fué más intenso desde los cereales de invierno hacia los hábitats seminaturales que desde los prados hacia a los hábitats semi-naturales, indicando que el hábitat adyacente moldea el movimiento de los depredadores hacia los hábitats seminaturales adyacentes.
The abundance and dispersal activity of O. majusculus were not different in maize plots with moderately high or low weed density. The carabids C. fuscipes, P. rufipes, P. cupreus and Metallina sp. and the anthocorid O. majusculus presented bidirectional movements between adjacent alfalfa and maize crops during the season. In contrast, C. septempunctata only moved from alfalfa to maize. The plant-dwelling O. majusculus and C. septempunctata that colonized maize at early vegetative stages came from alfalfa, indicating that alfalfa acted as a source of predators towards maize. However, in the reproductive growth stage period, maize acted as a source for C. fuscipes, P. rufipes, P. cupreus, Metallina sp. and O. majusculus moving to alfalfa, mainly after cuttings. After an alfalfa cutting, margins also acted as a refuge for carabids. Spillover of carabids, rove beetles and spiders was stronger from winter cereals to semi-natural habitats than from meadows to semi-natural habitats, indicating that neighbourhood identity shapes spillover effects to adjacent semi-natural habitats.
12
Nogueira, Madeira Filipe José. "Movement of predators in arable crop systems". Doctoral thesis, Universitat de Lleida, 2014. http://hdl.handle.net/10803/285265.
Testo completoAbstract (sommario):
L`abundància i dispersió d`O. majusculus no va ser diferent entre parcel-les de panís amb moderadament alta o baixa densitat de males herbes. Els caràbids, C. fuscipes, P. rufipes, P. cupreus i Metallina sp. i l`antocòrid O. majusculus presenten moviment bidireccional entre cultius adjacents de alfals i panís durant l'estació. En contrast, C. septempunctata només es va moure des de l`alfals cap al panís. Els individus d'O. majusculus i C. septempunctata que van colonitzar el panís a l'estadi vegetatiu provenien de l`alfals, indicant que l`alfals va ser la font d'aquests depredadors. No obstant, en el període reproductiu, el panís va actuar com una font de C. fuscipes, P. rufipes, P. cupreus, Metallina sp. i O. majusculus cap a l`alfals, principalment després de dall. El moviment de caràbids, estafilínids i aranyes va ser més intens des dels cereals d'hivern cap als hàbitats semi naturals que des dels prats cap als hàbitats semi naturals, indicant que l'hàbitat adjacent modela el moviment dels depredadors cap als hàbitats semi naturals.La abundancia y dispersión de O. majusculus no fué diferente entre parcelas de maíz con moderada alta o baja densidad de las malas hierbas. Los carábidos, C. fuscipes, P. rufipes, P. cupreus y Metallina sp. y el anthocorido O. majusculus presentan movimiento bidireccional entre cultivos adyacentes de alfalfa y maíz durante la estación. En contraste, C. septempunctata sólo se movió desde la alfalfa hacia al maíz. Los individuos de O. majusculus y C. septempunctata que colonizaron el maíz en el estadio vegetativo provinieron de la alfalfa, indicando que la alfalfa actúo como fuente de estos depredadores. Sin embargo, en el período reproductivo, el maíz actuó como una fuente de C. fuscipes, P. rufipes, P. cupreus, Metallina sp. y O. majusculus hacia la alfalfa, principalmente después de corte. El movimiento de carábidos, estafilínidos y arañas fué más intenso desde los cereales de invierno hacia los hábitats seminaturales que desde los prados hacia a los hábitats semi-naturales, indicando que el hábitat adyacente moldea el movimiento de los depredadores hacia los hábitats seminaturales adyacentes.
The abundance and dispersal activity of O. majusculus were not different in maize plots with moderately high or low weed density. The carabids C. fuscipes, P. rufipes, P. cupreus and Metallina sp. and the anthocorid O. majusculus presented bidirectional movements between adjacent alfalfa and maize crops during the season. In contrast, C. septempunctata only moved from alfalfa to maize. The plant-dwelling O. majusculus and C. septempunctata that colonized maize at early vegetative stages came from alfalfa, indicating that alfalfa acted as a source of predators towards maize. However, in the reproductive growth stage period, maize acted as a source for C. fuscipes, P. rufipes, P. cupreus, Metallina sp. and O. majusculus moving to alfalfa, mainly after cuttings. After an alfalfa cutting, margins also acted as a refuge for carabids. Spillover of carabids, rove beetles and spiders was stronger from winter cereals to semi-natural habitats than from meadows to semi-natural habitats, indicating that neighbourhood identity shapes spillover effects to adjacent semi-natural habitats.
13
Van, Gijn Evianne Laetitia. "The grooming process of internet sexual predators". Thesis, University of Cambridge, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708867.
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14
London, Josh M. "Harbor seals in Hood Canal : predators and prey /". Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/5394.
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Brown, S. L. "Predators and fisheries : an ecological evaluation of conflict". Thesis, Queen's University Belfast, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516865.
Testo completo
16
Broadbent, Heather. "A CTD Biotag for Mid-sized Marine Predators". Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/3992.
Testo completoAbstract (sommario):
Biologging tools for investigating the study of fine-scale linkages between animal behavior and the physical microstructure of the marine habitat are technically limited by substantial size, high cost or low sensor resolution. However, recent advances in electronic technologies and process techniques present attractive alternatives to current tag designs. Motivated by the need for a low-cost, compact CTD biotag for medium-sized marine animals, the University of South Florida Center for Ocean Technology developed a multi-sensor biotag for quantitative measurements of ocean salinity. This dissertation describes the development and performance of a novel CTD biotag used for animal-borne measurements of the physical microstructure of marine ecosystems.
Printed circuit board processes were used to fabricate a liquid crystal polymer- based conductivity, temperature and depth sensor board. Tests performed in the laboratory exhibited good sensor repeatability between the measured and the predicted variables indicating that the initial design and fabrication process is suitable for the construction of a CTD sensor board. The conductivity cells showed good sensor integrity for the entire conductivity range (0- 70 mS/cm), thus demonstrating the potential for a highly resolved salinity system.
The CTD sensor board was integrated into two initial multi-sensor biologging systems that consisted of reconfigurable modular circuit boards. The design and initial performance of a 4-electrode conductivity cell circuit was discussed and preliminary tests showed a sensor accuracy of 0.0161 mS/cm. A potential packaging material was analyzed for use on the temperature and pressure sensors and initial tests showed good sensor sensitivities (-2.294 °C/kohms and 1.9192 mV/dbar, respectively).
Underwater packaging of the biotag was presented in this work along with three different field observations. Vertical profiles of conductivity, temperature and depth in the Gulf of Mexico were obtained and compared to a commercial instrument. On the West Florida shelf, conductivity, temperature, depth and salinity data were obtained from loggerhead turtle deployments. Data collected showed that the tagged turtle encountered a highly variable salinity range (30.6- 35.3) while at depth (20 m). This data trend captured was in agreement with shelf characteristics (tidal fluxes and water mass features) and moored instruments. Finally, observations that were undertaken in Bayboro Harbor showed no biofouling to the conductivity electrodes during a 14 day deployment. This biotag is the first to use a PCB-based low-cost CTD to collect animal-borne salinity measurements.
17
Jiang, Bin [Verfasser]. "Predators promote trait diversification in prey / Bin Jiang". Berlin : Freie Universität Berlin, 2018. http://d-nb.info/1169832156/34.
Testo completo
18
Glanville, Philip William. "Computer simulation of protective coloration with human predators". Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243173.
Testo completo
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Klepac, Petra. "Interacting populations : hosts and pathogens, prey and predators". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38995.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2007.Includes bibliographical references.
The interactions between populations can be positive, neutral or negative. Predation and parasitism are both relationships where one species benefits from the interaction at the expense of the other. Predators kill their prey instantly and use it only for food, whereas parasites use their hosts both as their habitat and their food. I am particularly interested in microbial parasites (including bacteria, fungi, viri, and some protozoans) since they cause many infectious diseases. This thesis considers two different points in the population-interaction spectrum and focuses on modeling host-pathogen and predator-prey interactions. The first part focuses on epidemiology, i. e., the dynamics of infectious diseases, and the estimation of parameters using the epidemiological data from two different diseases, phocine distemper virus that affects harbor seals in Europe, and the outbreak of HIV/AIDS in Cuba. The second part analyzes the stability of the predator-prey populations that are spatially organized into discrete units or patches. Patches are connected by dispersing individuals that may, or may not differ in the duration of their trip. This travel time is incorporated via a dispersal delay in the interpatch migration term, and has a stabilizing effect on predator-prey dynamics.
by Petra Klepac.
Ph.D.
20
Davey, Jeffrey Stewart. "Intraguild predation among generalist predators in winter wheat". Thesis, Cardiff University, 2010. http://orca.cf.ac.uk/55042/.
Testo completoAbstract (sommario):
Modern annual arable crops are susceptible to outbreaks of pests due mainly to the uniform habitats that agricultural fields represent. Cereals are particularly prone to infestations of aphids, which may damage the crop directly through herbivory, or indirectly by acting as vectors of disease. These insects, however, have a large range of invertebrate natural enemies, which under certain circumstances, can maintain infestations below economically damaging levels. Greater habitat complexity at landscape and farm scale usually leads to more diverse assemblages of natural enemies at the field scale, but such diversity less often translates to a higher risk for pests. When higher natural enemy diversity is associated with lower levels of pest control, intraguild predation (IGP) is often cited as one of the primary antagonsitic mechanisms. IGP occurs where predators not only compete for the same resource, but also partake in a trophic interaction with one another. Controlled experiments suggest that the niche proximity of predators relative to each other and their shared prey may help predict the outcome of multiple- predator interactions. The primary aim of this thesis was to assess levels of IGP amongst generalist invertebrate predators and to elucidate their spatial patterns, in fields of winter wheat (
21
Hamdy, Ronald C., J. V. Lewis, Rebecca Copeland, Audrey Depelteau, Amber E. Kinser, T. Kendall-Wilson e Kathleen Whalen. "Patients With Dementia Are Easy Victims to Predators". Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/1236.
Testo completoAbstract (sommario):
Patients with dementia, especially Alzheimer’s disease and particularly those in early stages, are susceptible to become victims of predators: Their agnosia (see Case 1) prevents them from detecting and accurately interpreting subtle signals that otherwise would have alerted them that they are about to fall for a scam. Furthermore, their judgment is impaired very early in the disease process, often before other symptoms manifest themselves and usually before a diagnosis is made. Patients with early stages of dementia are therefore prime targets for unscrupulous predators, and it behooves caregivers and health care professionals to ensure the integrity of these patients. In this case study, we discuss how a man with mild Alzheimer’s disease was about to fall for a scam were it not for his vigilant wife. We discuss what went wrong in the patient/caregiver interaction and how the catastrophic ending could have been avoided or averted.
22
Li, Yunhe. "Ecological risks of insecticidal transgenic crops on arthropod predators /". [S.l.] : [s.n.], 2009. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Croy, Marion Isobel. "Characteristics of learning associated with feeding in marine predators". Thesis, Bangor University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236351.
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Meredith, Anna Louise. "Evaluation of predators as sentinels for emerging infectious diseases". Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/6480.
Testo completoAbstract (sommario):
New and emerging diseases in human and animal populations appear to be predominately associated with generalist pathogens that are able to infect multiple hosts. Carnivores are susceptible to a wide range of these pathogens and can act as effective samplers of their vertebrate prey, which are important reservoirs of many emerging diseases. This thesis evaluates the utility of carnivores as sentinels for pathogens present in their prey by exploration of four selected pathogen-prey-sentinel combinations in three rural study sites of varying habitat in northern England and Scotland over a twenty-two month period (2007-2009). Selected pathogens were Coxiella burnetii, Leptospira spp., Encephalitozoon cuniculi, and rabbit haemorrhagic disease virus (RHDV), selected prey species were wild rodents and rabbits, and selected carnivores were foxes, domestic cats and corvids. Seroprevalence to C.burnetii, Leptospira spp and E.cuniculi was assessed using adapted or novel test methodologies to enable their use for multiple mammalian species, however these were not applicable to corvids. RHDV seroprevalence was not assessed due to low acquisition of rabbit samples. Overall, seroprevalence to all three pathogens was significantly higher in predators than prey, at 24.2% and 12.4 % for C.burnetii, 22.73% and 1.95% for Leptospira spp and 39.06% and 5.31% for E.cuniculi in predator and prey species respectively. A similar pattern was found in all study areas and was consistent irrespective of individual prey or predator species, although serological evidence of exposure to E.cuniculi was not detected in domestic cats in any area. A semi-quantitative assessment of the time and financial costs of the study approach and application to hypothetical examples indicates that sampling carnivores is a much more costeffective approach to pathogen detection than sampling prey. The results indicate that carnivores can act as useful sentinels for broad-scale detection of pathogen presence and relative levels of prevalence in prey and predator populations. Careful selection of predator species and methods of sample acquisition are necessary to maximise their utility, and issues associated with diagnostic test performance and validation must also be acknowledged. Suggestions are made as to how this principle might be applied to future surveillance programmes. In addition, the study is the first report on the seroprevalence of C.burnetii, Leptospira spp and E.cuniculi in multiple wildlife species (field voles, bank voles, wood mice, foxes), the first detection of antibodies to C. burnetii in wildlife and cats, the first detection of antibodies to L mini, L hardjo prajitno and L hardjo bovis in wild rodents, and to L mini in cats, and the first detection of antibodies to E.cuniculi in wild rodents and foxes in the UK.
25
Parr, Raymond Arthur. "Moorland birds and their predators in relation to afforestation". Thesis, University of Aberdeen, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282068.
Testo completoAbstract (sommario):
The breeding bird assemblages of blanket bog and moorland habitats in the United Kingdom are of special international importance. They are characterised by species drawn from arctic to temperate regions breeding at high density and showing a particular affinity for open, in parts waterlogged, grazed and burned landscapes. Much recent debate has focussed on the effects of conifer plantations on the distribution and breeding success of these birds. This study concentrates on differences in breeding distribution and success of selected moorland birds. On blanket bog in Caithness and on heather moorland in Grampian Region, moorland waders Charadrii and red grouse Lagopus lagopus scoticus were counted using three methods cross-checked against each other; a) transects using trained dogs, b) listening for calls at dawn and dusk, and c) daylight transects without dogs. Counts were done on afforested ground and adjacent 'edge' areas, and on open moorland far from trees. In Caithness, densities of moorland waders on afforested ground started to decline as soon as planting began, and none was found inside plantations > 7 years old. Red grouse densities on afforested ground in Caithness and in Grampian rose higher than on open moorland areas during the first five years after planting, before declining. It is suggested that red grouse will disappear from afforested ground in Caithness 8-9 years after planting, and in Grampian 11-12 years after. On areas adjoining plantation < 8 years old in Caithness, densities and breeding success of waders and red grouse did not differ significantly from those on open moorland areas far from trees. However, next to older trees the densities of some waders were lower, and breeding success of golden plover Plurialis apricaria and red grouse lower than on open moorland. In Grampian, densities of red grouse did not differ between the different types of area, but breeding success was significantly lower on edge areas than on open moorland. Lower densities and poorer breeding in the two species mentioned above coincided with older nearby trees and taller ground vegetation. However, within areas there were no significant relationships between density and distance from the forest edge for any species, and similarly for breeding success.
26
Carter, Stephen Paul. "Habitat refuges and the management of predators for conservation". Thesis, Royal Holloway, University of London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269793.
Testo completo
27
Thomas, Matthew Brian. "Manipulation of overwintering habitats for invertebrate predators on farmland". Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316454.
Testo completo
28
Edwards, Francois K. "Fish presence and the ecology of stream invertebrate predators". Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/14773.
Testo completoAbstract (sommario):
This thesis describes the ecology of invertebrate predators (Plecoptera and Trichoptera) across steams, some without fish. Focusing primarily on stoneflies of the families Perlidae and Perlodidae, I studied the density and diversity of predators and the invertebrate prey, predator diet, size-mass relationships and microhabitat use. The abundance of invertebrate predators varied across streams and seasons but numbers of predatory invertebrates did not differ with fish presence. Only the smallest species of invertebrate predator was more abundant in substrate complexes in streams with fish. Overall biomass of invertebrate predators was lower in streams with fish, because the size-class distributions of some species were biased towards small individuals. The size-mass relationships and pre-emergent weights of all predators, except the Perlidae, varied across sites, but there was no clear relationship between condition and fish presence/absence. Invertebrate predators were mainly carnivorous in fishless sites, but in some species diet broadened with fish presence to include more algae. I hypothesise that the fixed nocturnal habit of Perlidae, permitted by their slower growth, accounted for the similarity in abundance, size, condition and diet across streams. Nocturnal activity and the coarse stony substrate which provided abundant refugia, minimised any effect of fish. By contrast, Perlodidae and other predators have shorter life cycles, forage by day and night, and have greater growth requirements, accounting for the greater variability in size and condition across streams. Though these species should incur greater exposure to fish, the coarse substrate may provide foraging space free from predation risk, thus minimising any effects of fish. For stream invertebrate predators, direct predation effects of fish appear to be minimal and principal effects may be sublethal, indirect, and prey mediated.
29
Jackson, Kelly. "Variable Consequences of Toxic Prey on Generalist Insect Predators". UKnowledge, 2016. http://uknowledge.uky.edu/entomology_etds/29.
Testo completoAbstract (sommario):
Introduced species, like the lady beetle Harmonia axyridis, have been linked to declines of native species through mechanisms including intraguild predation and competitive superiority. However, competitive differentials between species may be mitigated if subdominant species can utilize resources that dominant species cannot. Previous research has shown that some strains of the aphid Aphis craccivora are toxic to H. axyridis. My goal was to investigate use of this resource by both H. axyridis and other lady beetles, to determine whether these aphids might be an exploitable resource for subdominant lady beetle species. I first examined the behavioral responses of adult and larval H. axyridis to toxic strains of A. craccivora. I found that adults invested less time and laid fewer eggs with toxic than nontoxic aphids, and larvae consumed toxic aphids at a slower rate, often refusing them as a food source. I then tested whether six other lady beetle species could use the aphids, monitoring larval development in no-choice environments with different strains of A. craccivora. All species showed increased survival and development rates relative to H. axyridis on toxic aphid strains, suggesting these aphids may allow other coccinellid species to experience competitive release from the otherwise dominant H. axyridis.
30
Basson, Marinelle. "Population dynamics of krill interactions with its major predators". Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47352.
Testo completo
31
Aratchige, Nayanie Samantha. "Predators and the accessibility of herbivore refuges in plants". [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2007. http://dare.uva.nl/document/45176.
Testo completo
32
Flowers, Robbie Wayne. "Competitive interactions among two specialist predators and a generalist predator of hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae)". Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/26932.
Testo completoAbstract (sommario):
Competitive interactions among two specialist predators, Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Sasajiscymnus tsugae Sasaji and McClure (Coleoptera: Coccinellidae), and a generalist predator, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), of hemlock woolly adelgid were evaluated using laboratory, field and video studies. The two specialist predators are part of a biological control program for A. tsugae, and the potential for competition among these species and previously established generalist predators is unknown. In laboratory studies of predator groups in Petri dish assays, the only significant negative effects from competition occurred among conspecifics, resulting in reduced net egg production by L. nigrinus and H. axyridis and reduced feeding by H. axyridis. In contrast, heterospecific combinations showed non-interference. In longer duration field studies of predator groups, held in branch enclosures, predator survival and feeding were not significantly affected by additional predators. Net reproduction was again significantly reduced by conspecifics, while heterospecifics showed non-interference for all predator responses. All predators reduced the number of A. tsugae nymphs of the next generation relative to no-predator controls; however, L. nigrinus had much greater impact overall due to the large number of progeny produced. Video studies revealed that predator behavior varied qualitatively and quantitatively by species, and did not appear to be coordinated temporally or spatially. All species exhibited continuous activity patterns that were punctuated by longer periods of rest. The specialist predators were more selective of feeding and oviposition sites, and rested at more concealed locations than H. axyridis. Conspecifics significantly altered the time allocated to specific behaviors for L. nigrinus and H. axyridis, resulting in reduced predator effectiveness due to increased searching and decreased feeding and oviposition. All predator groups maintained a high degree of spatial separation relative to assay size, suggesting that chemical or tactile cues may be used to regulate their distributions. Overall, these studies suggest that the three predator species will be compatible in this system. Management implications include using multiple-predator species combinations over single-species for biological control of A. tsugae and implementing low-density releases to reduce the potential negative effects of intraspecific competition.Ph. D.
33
Malan, G., N. Seoraj-Pillai e Plessis MA du. "Alarm calls of Bronze Mannikins communicate predator size to familiar conspecifics". Taylor & Francis, 2009. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001767.
Testo completoAbstract (sommario):
Summary
This paper investigates, through experiments using surrogate predators, differences in intraspecific alarm calls between
familiar and unfamiliar Bronze Mannikin Spermestes cucculatus groups. Four groups of mannikins were captured with mist
nets from four areas in Durban (i.e. original groups) and randomly mixed (i.e. assorted groups). These groups were exposed
to latex terrestrial snakes and mounted aerial raptors, and their alarm calls and predator response behaviours recorded.
The Bronze Mannikins were able to discriminate between predators of different sizes, and increased their calling rate and
decreased the end frequency of the alarm call in response to larger predators. This perhaps signalled increased threat,
while simultaneously decreasing the conspicuousness of the flock. When the alarm call structure of the original and assorted
groups in response to both raptors and snakes was compared, birds in original groups called more often, but paused longer
between calls. Anti-predator behaviour differed in that assorted groups were less vigilant and aggressive toward the predators
and panicked more frequently. In these groups, a failure to transfer the predation threat information might have caused the
group to stop behaving cohesively and reliably. The manipulated experiments carried out in this study indicated that Bronze
Mannikins were able to communicate predator size risk to conspecifics, but not as successfully to unfamiliar group members,
showing that the investment, probability through altruistic payback, is greater in stable groups.
34
Cook-Sourice, Catherine. "The glass machinery in Christopher Dewdney's Predators of the adoration". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0006/MQ43524.pdf.
Testo completo
35
Hill, Simeon. "Search strategies of benthic predators : an experimental and modelling study". Thesis, Bangor University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245183.
Testo completo
36
Pickup, Zoe Lynette. "The relationship between potential bacterial pathogens and their amoebic predators". Thesis, Lancaster University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497151.
Testo completoAbstract (sommario):
The ecological relationships between amoebae and their bacterial prey has been sparsely investigated. Although these relationships are highly pertinent to the enfierging role played by protozoa in harbouring pathogenic bacteria, research has focussed largely on post-infection genetic and nfiolecular events within the protozoan cell. The v\/ork in this thesis aimed to throw light on the processes taking place prior to such events and the influencing factors. Amoebae are largely surface-dwellers, thus natural or man-made mixed bacterial biofilms where amoebae may be the principle predators, provide an ideal locus for these interactions, and the first paper established that amoebae do feed exclusively in attached mode.
37
Dixon, Claire Marie. "Investigation of phagosomal compartments and prey digestion in protozoan predators". Thesis, Lancaster University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551660.
Testo completoAbstract (sommario):
Protozoan grazing is commonly recognised as a major factor in shaping the structure and composition of bacterial communities. However, the complexity in the relationship between these predators and their prey means that ingestion of bacteria is not always coupled with complete digestion. A large number of factors are thought to be involved in determining the outcome of an ingestion event, and is highlighted by the fact that there is a large amount of inconsistency in the literature regarding the digestibility of prey types. Protozoan phagosome processing is poorly understood - which in turn makes it difficult to explain why and how differential digestion of prey occurs. Summation of the research into phagocytosis highlights two main implications for protozoan research. Firstly, in comparison to other phagocytic cell types, particularly macrophage and Dictyostelium discoideum, research in protozoan cells is out-dated, and therefore limited. Secondly, this lag in research means that gaps in the knowledge of protozoan phagosome processing are often filled with information from other model phagocytes; but are they comparable? This study firstly aimed to increase our understanding of phagosome processing by profiling changes in phagosome pH and size over time. Initially attempts were made to update research focusing on the pH profile in protozoa. However, work with both direct and indirect methods, previously utilised in other phagocytic cell types, failed to produce an effective assay for ,pH profiling in ciliates. Therefore, the main conclusions of this work explored the methodological considerations required when working with ciliated protozoa and the transferability of techniques between evolutionary distant phagocytic organisms. This research then progressed to assaying phagosome size over time as a measure of phagosomal processing. Results challenged the current beliefs regarding phagosome processing and produced a new model of phagosome sizing over time. Furthermore, utilising the sizing profile, as a relatively simple measure of phagosome processing events, factors that could potentially lead to an altered outcome were investigated. In this way, the pre-culture conditions of both predator and prey were shown to be significant in affecting phagosome processing. The next study examined the experimental variability that may be affecting the perceived outcome of digestion; rather than the events at the processing level. Specifically, by focusing on the digestibility of prey types as a function of the number of prey cells per phagosome it was shown that this latter parameter could alter the probability of prey digestion, with complete digestion of phagosomal contents being more likely if <6 prey cell contained. Finally, an in silico investigation aimed to take a holistic view to get a measure of how relevant and valid comparisons between phagocytic cell types are. Specifically, by analysing the proteins of a known phagosomal component, the V-ATPase enzyme. This work suggested that care must be taken when drawing general comparisons regarding phagocytosis and future work should strive to incorporate a larger number of protozoan and prey types. Overall the results of this study add further support to the idea that the relationship between prey and protozoan predators is one which has many layers of complexity which in turn has implications for nutrient transfer in environmental models.
38
Ayre, Kevin. "Evaluation of carabids as predators of slugs in arable land". Thesis, University of Newcastle Upon Tyne, 1995. http://hdl.handle.net/10443/946.
Testo completoAbstract (sommario):
An Enzyme-Linked Immunosorbent Assay (ELISA) was developed which detected slug antigens in postmortem gut analysis of carabid beetles. The ELISA was used to identify beetles which fed on slugs in three fields of oilseed rape and winter wheat in the Tyne valley, Northumberland. Generalist species such as Harpalus rufipes, Pterostichus melanarius, Pterostichus nladidus, Anlara silnilata and Nebria brevicollis fed on slugs in the field. Molluscan specialists such as Carabus violaceus and Cychrus caraboides also fed on slugs in the field. Laboratory studies indicated that many large and medium sized carabids were able to predate small slugs. Some beetle species did not eat slugs but exposure to the beetles increased slug mortality. Therefore, postmortem investigations may underestimate the impact that carabids exert on slugs as they do not measure the number of slugs killed. Slug mucus affected the locomotory activity of generalist and specialist beetle species. Beetles foraged longer, covered greater distances, made more turns, walked slower and spent more time stationary on soil covered in slug mucus compared to control areas. Abax parallelepipedus, P.melanarius, Pterostichus niger and H.rufipes all reduced slug damage to a chinese cabbage crop in a miniplot experiment compared with unprotected plots. However, these differences were not significant. A.parallelepipedus was most effective at reducing slug damage to the chinese cabbage but was rare in arable land. H.rufipes was least effective at reducing slug damage but was abundant in arable land in both years of the study. A high proportion of H.rufipes beetles fed on slugs in the field. None of these four species occurred at densities in the field which reduced slug damage in the miniplot experiment.
39
Roy, Helen Elizabeth. "Interactions between aphid predators and the entomopathogenic fungus Erynia neoaphidis". Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362048.
Testo completo
40
Harding, Nigel John. "The evolution of predators and their prey : a theoretical study". Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315075.
Testo completo
41
Hörnfeldt, Birger. "Cycles of voles, predators, and alternative prey in boreal Sweden". Doctoral thesis, Umeå universitet, Ekologi och geovetenskap, 1991. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-100711.
Testo completoAbstract (sommario):
Bank voles, grey-sided voles, and field voles had synchronous 3-4 year density cycles with variable amplitudes which averaged about 200-fold in each species. Cycles of vole predators (red fox and Tengmalm's owl), and their (foxes') alternative prey (mountain hare and forest grouse) lagged behind the vole cycles. The nomadic Tengmalm's owl responded with a very rapid and strong numerical increase to the initial cyclic summer increase of voles (the owl’s staple food). Owl breeding densities in the springs were highly correlated with vole supply in the previous autumns. This suggested that the number of breeding owls was largely determined in the autumn at the time of the owl's nomadic migrations, and that immigration was crucial for the rapid rise in owl numbers. The owl's numerical response was reinforced by the laying of earlier and larger clutches when food was plentiful. In addition, the owl has an early maturation at one year of age. The transition between subsequent vole cycles was characterized by a distinct shift in rate of change in numbers from low to high or markedly higher values in both summer and winter. Regulation increased progressively throughout the cycle since the rate of change decreased continuously in the summers. Moreover, there was a similar decrease of the rate of change in winter. Rate of change was delayed density-dependent. The delayed density-dependence had an 8 month time-lag in the summers and a 4 month time-lag in the winters relative to the density in previous autumns and springs, respectively. These findings suggest that vole cycles are likely to be generated by a time-lag mechanism. On theoretical grounds, it has been found that a delayed density- dependence of population growth rate with a 9 month time-lag caused stable limit cycles with a period between 3 and 4 years. Some mechanisms for the delayed density-dependence are suggested and discussed. The mechanisms are assumed to be related to remaining effects of vole populations past interactions with predators, food supplies, and/or diseases. Unlike the other voles, the bank vole had regular and distinct seasonal declines in density over winter. These declines are proposed to be due to predation, mainly by Tengmalm's owl. Supranivean foraging for epiphytic tree lichens and conifer seeds most likely explains why this species was frequently taken by the owl under snow-rich conditions. The alternative prey hypothesis predicts that a reduction of predator numbers should increase the number of alternative prey. Alternative prey should be less effectively synchronized to the vole cycle by predation at declining and low vole (main prey) densities; they may also lose their 3-4 year cyclicity. The appearance of sarcoptic mange among foxes in northern Sweden in the mid 1970s provided an opportunity to "test" these ideas, and these were found to be supported. In areas with highest mange infection rates, foxes declined markedly from the late 1970s to mid 1980s, whereas hare numbers rose rapidly and appeared non-cyclic.Diss. (sammanfattning) Umeå : Umeå universitet, 1991, härtill 7 uppsatser
digitalisering@umu
42
Melin, Jerker. "Phenotypic plasticity of blue mussels under threat from different predators". Thesis, Uppsala universitet, Institutionen för biologisk grundutbildning, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-316376.
Testo completoAbstract (sommario):
My study confirms that there are phenotypic plastic traits in blue mussels (Mytilus edulis) inresponse to predatory pressure from shore crabs (Carcinus maenas) and sea stars (Asteriasrubens) and a combination of them. Blue mussels can sense predators by olfactory cues fromthe predators themselves, or by alarm cues from attacked conspecifics, and then developinducible defences. In this experimental study, blue mussels were exposed to either nopredator (control) or to enclosed predators in terms of two shore crabs, two sea stars or thecombination of one shore crab and one sea star, over a period of six weeks. According to previous studies a good defence against predation from shore crabs should be athicker and also a more circular mussel shell, and a good defence against sea stars should be astrong posterior adductor muscle. All three predatory treatments resulted in mussel individuals with significantly heavier shells.When exposed to sea stars, individuals grew less lengthwise and showed a significantly lowerend volume, as well as a significantly heavier posterior adductor muscle. These mussels alsoshowed a tendency to survive sea star predation better in the predation test. Thus, induciblephenotypic defences against predation by sea star predation, were clearly demonstrated. Theexposure to shore crabs resulted in a significantly higher height of the mussels, whencontrolling for mussel length. The mussels exposed to shore crabs also showed end volumessimilar to control mussels, whereas an exposure to a combination of a crab and a sea starresulted in intermediate end volumes. This supports a phenotypic plasticity in traits related topredator threat. Individuals in all three predatory treatments were harder attached by morebyssus threads at the end of the experiment. Control mussels and those exposed to a singlecrab and sea star were repeatedly found to be more aggregated (i.e. fewer solitary mussels)over the course of the experiment, whereas the mussels presumably exposed to more olfactorycues from two shore crabs or two sea stars were more often found solitary and attached bybyssus threads. This study demonstrated inducible defences in how blue mussel allocate their resources todifferent dimensions of growth, shell weight, adductor muscle weight, as well as aggregationand byssus attachment, depending on predatory threat.
43
Blake, Michael A. "Defence against predators by juvenile signal crayfish (Pacifastacus leniusculus, Dana)". Thesis, University of Leicester, 1993. http://hdl.handle.net/2381/34156.
Testo completoAbstract (sommario):
This study investigated the defensive responses of juvenile signal crayfish (Pacifastacus leniusculus, Dana) to two putative predators, perch (Perca fluviatilis, L.) and eel (Anguilla anguilla, L.), and attempted to determine the Importance of direct and indirect predatory effects on the distribution of newly independent Juvenile crayfish in a Swedish pond. Eels are thought to be more detrimental to crayfish populations than perch. Experiments using juvenile crayfish did not support this assertion. Visual and chemical stimuli elicited crayfish avoidance behaviour. This was most marked when both stimuli were presented together. Both predators elicited similar avoidance behaviour. Crayfish were less active by day, spending more time under shelter. Shelter provided by vegetation and substrata reduced crayfish mortality. Crayfish also avoided small non-predatory fish (Leucaspius delineates, Heckel). It is suggested that these fish indirectly increased crayfish mortality. Adult crayfish increased juvenile crayfish mortality but caused juveniles to be more active by day than at night. These responses illustrate the conflicting demands on crayfish defensive behaviour in multi-predator environments. Mechanical and visual stimuli elicited evasive behaviour. Crayfish evaded predatory strikes by perch and eels. The response to eels was delayed. Perch chased fleeing crayfish, and caught more crayfish than eels, which never chased prey. Initially, perch preyed on juvenile crayfish more rapidly than eels. Despite having distinct foraging behaviours, perch and eels produced similar crayfish mortalities. If eels are more detrimental than perch to crayfish populations, this may be a result of differences in size selective predation. The initial distribution of newly independent crayfish in a Swedish pond was influenced by the distribution of gravid female crayfish. Perch preyed on juvenile crayfish but were not a major factor determining crayfish distribution. Intraspecific competition and Invertebrate predation may have had a greater effect. Crayfish populations may be influenced by perch predation on yearling crayfish.
44
Stake, Mike M. "Golden-cheeked warbler nest predators and factors affecting nest predation /". free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p1418066.
Testo completo
45
Mella, Valentina S. A. "Physiological and behavioural responses of Australian and exotic prey to the scent of native and introduced predators". Thesis, Curtin University, 2009. http://hdl.handle.net/20.500.11937/350.
Testo completoAbstract (sommario):
This study examined the physiological and behavioural effects of a stress-inducing stimulus (predator odour) on potential prey species (Australian native and exotic). The aim was to determine if differences in the response of prey were related to the scent of evolutionary known predators compared to unfamiliar or short-term introduced ones. In laboratory experiments, responses were always restricted to changes in respiratory variables, with brushtail possums (Trichosurus vulpecula), rabbits (Oryctolagus cuniculus) and tammar wallabies (Macropus eugenii) showing no variation in metabolic rate after exposure to predator odours.Brushtail possums showed strong changes in ventilatory rate only when faced with the scent of an historical predator, increasing respiratory frequency (ratio after/before exposure = 4.55 ± 1.007) and decreasing tidal volume (ratio after/before exposure = 0.38 ± 0.113 ) in response to stale dingo urine. The changes were short-lived, lasting for only one minute of exposure. For this reason, it is unclear if the response observed could be considered as a fear reaction. However, there was no habituation after three exposures and this may indicate that possums were initially displaying an investigative approach to a predator scent and then relaxing once assessment was completed.The effect of predator and novel odours on the ventilation of rabbits appeared to be in general mediated by anxiety, as shown by the responses elicited by both predator and control scents. However, stronger reactions were observed in response to feral cat and quoll odours for both respiratory frequency (ratio after/before exposure to feral cat = 4.39 ± 0.721 and to quoll = 3.75 ± 0.486) and tidal volume (ratio after/before exposure to feral cat = 0.47 ± 0.065 and to quoll = 0.64 ± 0.129). This could be due to different intensity of the olfactory stimuli. Nevertheless, the effects of noxious odours on rabbits clearly demonstrate that they become highly vigilant at any sudden change in their environment.Tammar wallabies appeared to possess a mechanism for the recognition of predator odours as ventilatory responses were restricted to particular predator scents. After investigation, fox and cat odour provoked a stronger and more prolonged change in respiratory frequency (ratio after/before exposure to fox = 3.58 ± 0.918 and to feral cat = 2.44 ± 0.272) and tidal volume (ratio after/before exposure to fox = 0.84 ± 0.110 and to feral cat = 0.98 ± 0.155) compared to the other scents, suggesting that wallabies may have perceived these species as more immediate threats.For wild, free-living brushtail possums and southern brown bandicoots (Isodoon obesulus), there was no pattern of avoidance of historical or introduced predator odours, with no difference in number of animals captured in predator and control scented traps. This may indicate that predator odour avoidance has not evolved in these species and that they have poor possibilities of escaping potential predators. However it may also be explained by the long-term predator-free environment in which the study was conducted, and suggests loss of anti-predator behaviour in populations without predation risk.Wild, free-ranging western grey kangaroos (Macropus fuliginosus) reacted to the odour of both historical (dingo) and novel (fox) predators by reducing number of feeding events (5.2±2.08 for fox and 5.9±1.33 for dingo) and time spent foraging (17.7±7.2 sec for fox and 22.2±4.6 sec for dingo) when predator scents were present and by escaping areas tainted with predator odours (41.4±17.5 sec for fox and 33.8±13 sec for dingo). Clearly these results suggest that kangaroos are scared of predator odours. However, a close investigation of predator scents was necessary before a response could be elicited and feeding areas were not completely abandoned.It is still unclear if small Australian prey, such as southern brown bandicoots and brushtail possums, respond to olfactory cue of predation in the wild, as different results were obtained in the studies conducted in the laboratory and in free populations. However, this research showed that medium and large-sized macropods respond to both native, long-term and introduced predator odours. This indicates that at least some Australian prey species can recognise the odour of potential predators, although responses usually occur after a period of investigation, and do not always result in avoidance behaviour. Differential responses appear to be based on the perceived risk. Use of predator odour is unlikely to be an effective mechanism of deterring herbivores from preferred feeding locations.
46
Guilford, T. "Aposematism". Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382678.
Testo completo
47
Kelly, D. W. "The role of native and invasive amphipods (Crustacea) in freshwater communities". Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390875.
Testo completo
48
Coombes, D. S. "Factors limiting the effectiveness of Demetrias atricapillus (L.) (Coleoptera: Carabidae) as a predator of cereal aphids". Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376159.
Testo completo
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Smee, Delbert Lee. "The Ecology of Yikes! Environmental Forces Alter Prey Perception of Predators". Diss., Connect to this title online, 2006. http://etd.gatech.edu/theses/available/etd-05082006-213823/.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Georgia Institute of Technology, 2006.Title from PDF t.p. (viewed on Oct. 28, 2006). Marc Weissburg, Committee Chair ; Mark Hay, Committee Member ; Lin Jiang, Committee Member ; David Dusenbery, Committee Member ; Don Webster, Committee Member. Includes bibliographical references (p. 115-122).
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Sarfati, Michal. "Diapause by seed predators and parasitoids in Chionochloa mast seeding communities". Thesis, University of Canterbury. Biological sciences, 2008. http://hdl.handle.net/10092/2194.
Testo completoAbstract (sommario):
Chionochloa, a genus of snow tussock grasses native to New Zealand, exhibits pronounced mast seeding. Chionochloa suffers very high levels of pre-dispersal flower and seed predation by three main insects: Eucalyptodiplosis chionochloae, a cecidomyiid midge, which is formally described here; Megacraspedus calamogonus, a gelechiid moth and Diplotoxa similis, a chloropid fly. Seven species of parasitoids that attack these seed predators were discovered. Four species parasitize M. calamogonus (one tachinid fly and three hymenopteran wasps), one parasitizes D. similis (Hymenoptera: Eulophidae) and two parasitize E. chionochloae, (a pteromalid wasp Gastrancistrus sp. and a platygastrid wasp Zelostemma chionochloae, which is given a formal description here). The abundance, predation levels by each of the insect species, and interactions between all the organisms in the community were studied across three elevations at Mount Hutt over three summer seasons. M. calamogonus was most abundant at 450 m altitude during all three seasons. D. similis was most common at 1070 m altitude, while its predation levels peaked in low flowering seasons and decreased in high seasons. E. chionochloae was abundant in all three altitudes and increased its predation levels with increasing flowering intensity. E. chionochloae was confirmed to use prolonged diapause of at least three years. Prolonged diapause was also confirmed in its two parasitoids. Chionochloa plants were manipulated with various treatments to test the effect on diapause in E. chionochloae and its two parasitoids. Treatments included plant warming, root pruning, gibberellic acid sprayed on the plants and combinations of these treatments. All three insects changed their emergence in response to some treatments and therefore it was suggested that combined with risk-spreading diapause, they may use some predicting to emerge from prolonged diapause. E. chionochloae control their diapause following some of the cues that Chionochloa use for flowering, while Z. chionochloae and Gastrancistrus in some cases follow their host’s cues and in others use similar cues as Chionochloa plants. Emergence or diapause predictions differed across elevations and plant species in all three insect seed/flower predators. E. chionochloae had female-biased sex ratios in different populations even after prolonged diapause. There was week evidence that both parasitoid species are female-biased in the first emergence year and male-biased after more than one year in diapause. Therefore it was suggested that diapause is not more costly for females of E. chionochloae and its parasitoid than for males. Females of all three species were not found to be better predictors (i.e, more likely to respond to treatments by not entering extended diapause) than males. The complex interactions of all the organisms in this web are thought to be sensitive to climate, and it was suggested that the global climate change may alter this sensitive system.