Thesis (M.S.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references.

Thesis (M.S.)--Rochester Institute of Technology, 2006. / Includes bibliographical references.

Thesis (M. Sc.)(Wildlife Management)--University of Pretoria, 2005. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Made available in DSpace on 2014-06-11T19:35:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-08-20Bitstream added on 2014-06-13T18:47:10Z : No. of bitstreams: 1 pereira_lftr_dr_rcla.pdf: 1890208 bytes, checksum: 494aae6f71d5d96e2d79e4d2660b0777 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Até a presente tese, a informação sobre predação e estratégias defensivas em anuros estava fragmentada e desconexa na literatura científica. Na ausência de uma revisão sobre o tema, algumas especulações foram geradas baseadas nas impressões pessoais de diversos pesquisadores. Por exemplo, existem muitos ou poucos relatos de anuros sendo apresados? Um determinado comportamento defensivo já foi descrito em algum lugar, ou é inédito? Qual a relação entre os predadores e os mecanismos de defesa dos anuros? Essas e outras perguntas estavam em aberto. Mesmo em livros texto, os quais geralmente revisam os assuntos abordados de forma abrangente, nota-se o parco conhecimento sobre o tema, sendo estes sempre os menores capítulos dos livros e de conteúdo razoavelmente superficial. Todavia, muita informação já foi gerada e muita ainda está por vir. É nesse sentido que idealizamos e realizamos o presente estudo, visando reunir grande parte do conhecimento atual e gerar novas previsões e hipóteses testáveis. Assim, relacionamos os predadores atuais e naturais dos anfíbios anuros (incluindo as desovas e pós-metamórficos) e revisamos as principais estratégias defensivas dos adultos (pós-metamórficos). Muitos dados apresentados são inéditos e outros compilados da literatura, mas ambos analisados de maneira integrada e sempre dando enfoque evolutivo nas discussões apresentadas. Consideramos este estudo um ponto inicial para compreendermos mais profundamente as estratégias defensivas dos anuros e sua relação com os predadores naturais. / Until the present moment, the information about defensive strategies and predation upon anurans was fragmented and disconnected in the scientific literature. In the absence of an overview of the subject, some speculations have been raised based on personal points of view of several scientists. For example, are there many or few reports of predation upon anurans? A specific defensive behavior has already been described or not? How is the relationship between the defensive strategies and predator mechanisms? These and odder questions were hard to answer. Even in text books, where the subjects are treated in a broad way we can notice the poor knowledge of the subject and these are always the shorter and superficial chapters. However, many information is already available and many is about to come. Therefore, we idealized and did the present thesis, aiming to joint a large part of the current knowledge and promoting some previsions and testable hypotheses. So, we related the actual and natural predators of anurans (including eggs and post-metamorphics) and reviewed the main defensive strategies of the adults (post-metamorphics). A great amount of the data presented is novel and other set of data were found in the available literature, but both were analyzed simultaneously with an evolutive approach. We consider this thesis a starting point of a deeper comprehension of the anurans defensive strategies and their relationship with natural predators.

This study was aimed at providing information that could be used to estimate the predation effect of squawfish on sockeye salmon. Initial studies at Griffen Lake revealed that the percentage of the population acting as predators, and the average stomach volume, increased with increasing size in non-spawning squawfish. Squawfish in Griffen Lake appeared to be most active at night. For the most part, a force fed volume (2.0 ± .1 gms) was digested by all sizes of squawfish in less than 24 hours. Further studies at Cultus Lake in the laboratory revealed that the rate of digestion was dependent on temperature, volume of food, and size of fish. At 6°C a lag prior to digestion commencing was observed and digestion was not complete for the medium volume in less than 52 hours. On an average the medium fed volume was digested in less than 24 hours for temperatures greater than 15°C. Medium volume corresponded to approximately twice the smallest volumes recorded in stomach contents in the field. A life span of ten years for males and 14 years for females with no differential in the growth rate was determined from the banding patterns and sections of pharyngeal teeth. Consumption rates and periodicity of feeding and activity were within the limits of data from Griffen Lake. Laboratory calculated routine metabolic rate was approximately twice the theoretical rate for pooled species. A tagging experiment at Cultus Lake revealed a population of approximately 20, 000 squawfish greater than 720 cm that, on an average, grew less than 0.36 cm during the winter. Growth during the summer was assessed to be in the form of weight increase of body tissue and gametes. Trap catches and temperature preference experiments indicated that squawfish are found within particular temperature regimes in different phases of the year. Within Cultus Lake, distance did not prevent squawfish aggregation on concentrations of sockeye smolts. There was increased consumption of smolts during smolt migration from the lake. In the field a significant difference in rate of digestion for different sizes of squawfish could not be demonstrated; however, there was a difference in the volume voluntarily consumed. With these findings and other theoretical information, it is possible to determine quantitatively the predation effect of a squawfish population on sockeye. Having established a population estimate, an estimate of annual mortality (55.2 per cent per year), and the temperature specific phases (early smolt phase, peak smolt phase, spawning phase, summer phase, fall phase, winter phase), two methods for the assessment of the predation effect were possible. First, knowing proportion of the size classes acting as predators, the numbers and frequency distribution of squawfish remaining within any phase, the duration and temperature characteristics of the phase, the effect of temperature on the rate of digestion, and the volumes that can be digested in 24 hours, it was possible to get an accumulated volume consumed for the population. For the 20, 000 squawfish greater than 20 cm fork length in Cultus Lake, this represents an approximate consumption of 1.4 million sockeye smolt equivalents. The second estimate of consumption was based on the energy requirements converted to consumption rates using conversion coefficients for the same population. The energy requirements to complete spawning, growth and mean metabolism were summed, then converted to a consumption volume for the population. The findings revealed that approximately 2.8 million sockeye equivalents are required. / Science, Faculty of / Zoology, Department of / Graduate

Various aspects of rainbow trout (Salmo gairdneri) predation on migrating sockeye salmon (Oncorhynchus nerka) fry and rainbow trout eggs were studied during 1970-71 in specially-constructed artificial streams, and in the laboratory. Tests involving sockeye fry as prey were conducted near Babine Lake, British Columbia, while those using rainbow trout eggs were done near Abbotsford, British Columbia. Examination of the effects of physical factors such as water velocity, water turbidity, and light intensity on predation on migrating sockeye fry showed mortality to be inversely related to water velocity and water turbidity; inversely related to light intensity at low light levels but directly related at very low levels. Other stream tests showed mortality to be inversely related to the amount of exposure of predators to fry, before the beginning of a nightly fry migration. Exposing predators to abnormal light for varying periods of time, immediately prior to fry migration, reduced over-all mortality during fry migration. Mortality was not proportional to the length of exposure of predators to abnormal light. Fry experience with predators was shown to increase the ability of fry to escape or avoid predation on subsequent predator encounters. Additional experience served to further increase their ability to escape or avoid predators. Conclusions drawn from stream tests and a behavioral study are that experienced fry migrate in a manner rendering them less susceptible to predation and the migration pattern (compact and in mass) is influenced in part, or completely, by encounter and escape from predator-prey interactions experienced earlier. "Handling" or other fright-evoking stimuli appeared to have similar effects. Rainbow trout feeding on colored fish eggs indicated color preference patterns which are influenced by background coloration (color contrast between food and background), and light intensity. Preference was for colors showing the most contrast with the background at a particular light intensity. At low light levels, on a pale-blue background, preference was for lighter colors, while it was for darker colors at high light levels. Mortality differences increased proportionately with contrast between colors. Finally, trout displayed what appears to be a behavioral preference for red, and possibly blue, regardless of surrounding environmental conditions. In a food deprivation study rainbow trout displayed an S-shaped hunger response curve when fed on eggs. Indications were that rainbow trout will feed to gut capacity when given the opportunity. Finally, beyond an upper limit of food deprivation, the amount of food eaten by an individual remains fairly constant. / Science, Faculty of / Zoology, Department of / Graduate

The predatory functional response is one of the important components of the interaction between predator and prey populations. This response has not been measured for fish predators and fish prey, in spite of the demonstrated importance of predation in regulating numbers in populations such as the juvenile salmon system used in this thesis. Laboratory exeriments were conducted to determine the form of the functional response of the prickly sculpin (Cottus asper), a common freshwater predator, to density of sockeye salmon fry, Oncorhynchus nerka. An alternative prey, chum salmon eggs (Oncorhynchus keta), were presented to the predator with the salmon fry, in order to facilitate switching at low fry densities and possibly lead to a sigmoid (type III) response. Initial experiments showed that sculpin feeding rate did not substantially differ from day to night; that in the absence of food, hunger increased to a maximum after about seven days' starvation; and that a density of 400 chum salmon eggs in a 2000 1 tank produced maximum consumption level by sculpins of 160 mm total length. The functional response experiments did not indicate a sigmoid rise in consumption over low fry densities. However, the initial decelerated rise in consumption was followed by an anomalous drop in response and a subsequent rise in response. It is suggested that this may result from the summation of separate responses through different sensory modalities, or from interference with predation by fry at intermediate densities. This shape of functional response may imply a stable local equilibrium at intermediate densities of salmon. Sculpins probably have a significant impact on fry numbers only at very localized points in space and time, such as at the outlets of tidal creeks on a falling tide. / Science, Faculty of / Zoology, Department of / Graduate

The history, management and ecology of the European red mite, Panonvchus ulmi Koch, and two important phytoseiid predators, Typhiodromus caudiglans Schuster and Typhiodromus occidentalis Nesbitt were reviewed. The roles and interactions of dispersal, predation and weather in the orchard mite system were examined. Field experiments in an apple orchard with well-established phytoseiid and European red mite (ERM) populations showed that Typhiodromus rarely move among or between trees and the ground cover, either by air or via the trunk. They were incapable, within a single season, of repopulating trees from which phytoseiids had been removed by early-season carbaryl application, even though these trees supported high prey populations and were interspersed among unsprayed trees well-populated with Typhiodromus and the ERM. Large numbers of sticky traps captured very few aerially dispersing phytoseiids. In contrast, their ERM prey actively dispersed within trees and throughout the orchard. Mite densities were uncorrelated with leaf chlorophyll content; within-tree dispersal was not directly determined by leaf condition. Adult females were greatly over-represented in aerially-dispersing ERM emigrants in comparison with populations on the apple trees. No density threshold effect on ERM dispersal was discernible on a per-tree basis. Aerial dispersal was extensive and appeared to depend on the weather more mites disperse on warm and calm days than on cool or windy days. ERM dispersal via the tree trunk was minimal and the presence of weeds resulted in only a slight increase in ERM density on the trees. The phytoseiids affected the ERM by reducing population densities, by reducing the proportion of immatures, and by decreasing the degree of prey aggregation (as represented by frequency distribution of leaf counts). The consequences of low predator dispersal and high prey dispersal in a weather-dependent system are discussed. Results of computer simulation of the development, predation, and dispersal are presented. Dispersal (immigration and emigration) allow the phytoseiid populations in the single-tree model to persist and control the ERM. In simulations of the interaction of Typhlodromus with the ERM, the interaction of dispersal and temperature-related processes is strong and non-linear, and may operate through several processes. / Land and Food Systems, Faculty of / Graduate

No description available.

No description available.