Tesi sul tema "Predators"

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.

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.

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.<br>2031-01-02

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-mimicry<br>Huvudsyftet 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

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.

Bibliography: pages 187-191.<br>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.

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.

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.<br>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.<br>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.

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.<br>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.<br>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.

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.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2007.<br>Includes bibliographical references.<br>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.<br>by Petra Klepac.<br>Ph.D.

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 (<italic>Triticum aestivum</italic>), an important cereal crop in North-West Europe. The chief objective was to establish the regulatory abilities of these predators in the control of aphids. Post-mortem gut content analysis using PCR was used to establish the intensity of IGP by two polyphagous predators, the carabid beetles <italic>Pterostichus melanrius</italic> and <italic>P. madidus</italic>, on a number of insectivorous linyphiid spiders and their shared aphid prey. Each of the spiders tested was found to suffer IGP. Predation rates were adjusted using data from controlled feeding trials and resampled using Monte Carlo models to test the hypothesis that predation was density-dependent. In one experiment, the web-occupying linyphiid <italic>Tenuiphantes tenuis</italic> was consumed by up to a third of <italic>P. melanarius</italic>. Predation rates by carabids on the linyphiid <italic> Bathyphantes gracilis</italic> were consistently lower than expected. <italic> B. gracilis</italic> also relies principally on its web to capture prey, but builds these webs significantly higher in the wheat stem than <italic>T. tenuis </italic>. Preferences for intraguild prey species more likely to hunt aphids on the ground, the tetragnathid spider <italic>Pachygnatha degeeri</italic>, and the linyphiids Erigone spp. (<italic>E. atra</italic> and <italic>E. dentipalpis </italic>), were less consistent than those species more dependent on their webs to hunt aphids and other prey. While many factors may contribute to the outcomes of multi-predator interactions, these findings broadly supported the hypothesis that niche proximity of intraguild predators is positively related to levels of disruption due to intraguild interactions.

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.

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.

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 <i>Charadrii</i> and red grouse <i>Lagopus lagopus scoticus</i> 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 <i>Plurialis apricaria</i> 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.

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.

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.

Competitive interactions among two specialist predators, <i>Laricobius nigrinus</i> Fender (Coleoptera: Derodontidae) and <i>Sasajiscymnus tsugae</i> Sasaji and McClure (Coleoptera: Coccinellidae), and a generalist predator, <i>Harmonia axyridis</i> 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 <i>A. tsugae</i>, 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 <i>L. nigrinus</i> and <i>H. axyridis</i> and reduced feeding by <i>H. axyridis</i>. 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 <i>A. tsugae</i> nymphs of the next generation relative to no-predator controls; however, <i>L. nigrinus</i> 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 <i>H. axyridis</i>. Conspecifics significantly altered the time allocated to specific behaviors for <i>L. nigrinus</i> and <i>H. axyridis</i>, 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 <i>A. tsugae</i> and implementing low-density releases to reduce the potential negative effects of intraspecific competition.<br>Ph. D.

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.

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.

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.

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.

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.<br><p>Diss. (sammanfattning) Umeå : Umeå universitet, 1991, härtill 7 uppsatser</p><br>digitalisering@umu

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.

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.

This thesis is organized in three clearly differentiated chapters. The three of them deal with currently relevant issues: The effect of low-quality of standardized tests on research, the high levels of political corruption in Spain and the collective capacity of tackle climate change. In the first chapter “Straightening PISA: When Students do not Want to answer Standardized Tests”, I study one of the key elements on current education policies: The standardized-tests. Concretely, I analyze how students approach standardized tests in different ways. I use a measure of effort exerted by students belonging to different countries and social groups in order to assess the impact of low effort on the student's final score. The measure links an acknowledged psychological tests (Dot-Counting test) with one PISA-item, in which students had to merely count dots. In this chapter, I measure to which extent different effort levels may distort the score of students. This problem would affect social-science research when standardized-tests are use. At the end of the chapter, I propose a simple solution to design standard tests which would eliminate this problem. Given the importance of standardized-tests on the design of education programs, this paper may be a contribution to implement more accurate education policies. The second chapter focuses on one key issue of Spanish current political crisis: The level of political corruption. Political institutions developed during the Spanish transition to democracy are currently criticized due to their inability to stop political corruption. For instance, Spanish Attorney Generals are appointed by the government and their impartiality is usually criticized. In “Stories on Corruption: How Media and Prosecutors Influence Elections”, I analyze systematically the partiality of the last two Attorney Generals. Concretely, I study whether Attorney Generals try to influence elections by adjusting the tempo of their investigations to the electoral calendar. This possibility is combined with the mass media editorial decisions. I analyze whether mass media have a partisan bias and hide corruption activities of their preferred parties. For doing so, I have created a unique database: I have coded the number of articles containing the word “corruption” of the two main Spanish newspapers “El Pais” and “El Mundo" every week in the last ten years. After the econometric analysis I found significant evidence of the partisan behavior of both the Attorney Generals and mass media. The last chapter is a joint work with Karolina Safarzynska from the Wirtschaftsuniversität Wien. “Responding to the Climate Change Challenge: Experimental Evidence” tackles the problem of climate change and the capacity of societies to overcome it. This chapter has also a different methodology. Precisely, it is based on experimental methods. We consider isolated groups of individuals which must extract resources form a renewable common-pool. The novelty is the study of the impact of resource uncertainty on individual harvests in common-pool resource dilemmas together with the possibility of group collapse. The uncertainty is modeled as a weather shock diminishing the groups' resources, which is drawn from the distribution known in advance to participants. On the other hand, the group collapses if the resources go below a certain threshold. In that case all accumulated resource-extraction get lost. This can be interpreted as the minimum harvests below which a group does not have sufficient nutrition to survive. We find that in the long run, sufficiently severe weather shocks can induce individuals to conserve resources. However, in the short-run uncertainty leads to resources over-exploitation. In addition, our results suggest that resource uncertainty undermines effectiveness of costly sanctioning. In some treatments, individuals can punish others at their own cost. We found that the possibility to punish others induce individuals to harvest significantly more resources in the beginning of the experiment, compared to the situation when sanctioning is not possible. The presence of punishment paradoxically increases the probability of resource exhaustion. We interpret these results in the context of the World climate change. We conclude that the positive impact of environmental pressure on individual behavior and the effect of new institutions are likely to come too late to prevent damage to the environment.<br>Questa tesi è organizzata in tre capitoli chiaramente differenziati. I tre capitoli riguardano argomenti attualmente rilevanti: l’effetto della bassa qualità dei test standardizzati in ricerca, gli alti livelli di corruzione politica in Spagna e la capacità collettiva di rispondere ai cambiamenti climatici. Nel primo capitolo “Rafforzando PISA: quando gli studenti non vogliono fare i test standardizzati”, studio uno degli elementi chiave nelle attuali politiche per l’educazione: i test standardizzati. Concretamente, analizzo come gli studenti affrontano i test standardizzati in modi differenti. Uso una misura di sforzo fatto degli studenti che appartengono a Paesi diversi e gruppi sociali diversi per stimare l’impatto del basso sforzo nel punteggio finale degli studenti. La misura collega un test psicologico molto affermato (il test di conta dei punti) con una domanda del test PISA, nella quale gli studenti devono semplicemente contare i punti. In questo capitolo, misuro fino a che punto diversi livelli di sforzo fatto degli studenti possono distorcere il punteggio del PISA. Questo problema avrebbe degli effetti sulla ricerca nelle scienze sociali, quando vengono utilizzati i risultati dei test standardizzati. Alla fine del capitolo, propongo una semplice soluzione per il design di test standardizzati che elimini questo problema. Data l’importanza dei test standardizzati nel design dei programmi educativi, questo articolo potrebbe essere un contributo per implementare politiche educative più accurate. Il secondo capitolo si focalizza su uno dei temi chiave della attuale crisi politica spagnola: il livello di corruzione. Le istituzioni politiche sviluppate durante la transizione spagnola verso la democrazia sono attualmente sotto forte critica a causa della loro incapacità nel fermare la corruzione politica. Per esempio, i procuratori generali spagnoli sono nominati dal governo e la loro imparzialità è spesso criticata. Nel capitolo “Storie sulla corruzione: come i media e I procuratori influenzano le elezioni”, analizzo sistematicamente la parzialità degli ultimi due procuratori generali. Concretamente, studio se i procuratori generali tentano di influenzare le elezioni modificando la tempistica delle loro indagini adattandola al calendario elettorale. Questa possibilità è combinata con le decisioni editoriali dei mass media. Analizzo se i mass media hanno un pregiudizio ideologico e nascondono le storie di corruzione dei loro partiti preferiti. Per fare questo, ho creato un database unico: ho codificato il numero di articoli contenenti la parola “corruzione” nei due quotidiani principali spagnoli, “El Pais” e “El Mundo”, ogni settimana negli ultimi dieci anni. Dopo un’analisi econometria ho scoperto una evidenza significativa di un comportamento partigiano sia dei procuratori generali che dei mass media. L’ultimo capitolo è un lavoro congiunto con Karolina Safarzynska della Wirtschaftsuniversität Wien. “Rispondendo alla sfida del cambiamento climatico: evidenze sperimentali” affronta il problema del cambiamento climatico e la capacità delle società di superarlo. Questo capitolo usa una metodologia differente. Precisamente si basa su metodi sperimentali. Noi consideriamo gruppi isolati di individui che devono estrarre risorse da un bacino di risorse rinnovabili. La novità è lo studio dell’impatto dell’incertezza di risorse sui raccolti individuali nei dilemma dei bacini di risorse rinnovabili, unita alla possibilità che il gruppo collassi. L’incertezza è modellata come uno shock atmosferico che diminuisce le risorse dei gruppi, che è estratto da una distribuzione conosciuta in anticipo dai partecipanti. D’altro canto il gruppo collassa se le risorse scendono sotto una certa soglia. In quel caso tutta l’estrazione accumulata di risorse viene persa. Questo potrebbe essere interpretato come il minimo raccolto sotto al quale il gruppo non ha nutrimento sufficiente per sopravvivere. Scopriamo che nel lungo termine, shock atmosferici abbastanza severi possono indurre gli individui a conservare le risorse. Comunque, nel breve termine l’incertezza porta ad un sovrasfruttamento delle risorse. Inoltre, i nostri risultati suggeriscono che l’incertezza nelle risorse danneggia l’effettività del sanzionamento costoso. In alcuni trattamenti, gli individui possono punire altri pagando un costo. Scopriamo che la possibilità di punire altri induce gli individui a raccogliere significativamente più risorse all’inizio dell’esperimento, comparato alla situazione in cui il sanzionamento non è possibile. La presenza della punizione paradossalmente incrementa la probabilità di un esaurimento delle risorse. Interpretiamo questi risultati nel contesto del cambiamento climatico mondiale. Concludiamo che l’impatto positivo della pressione climatica sul comportamento individuale e l’effetto di nuove istituzioni probabilmente arrivano troppo tardi per prevenire un danno all’ambiente.

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.

Thesis (Ph. D.)--Georgia Institute of Technology, 2006.<br>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).