1950-1979
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Browsing 1950-1979 by Author "Baldwin, Paul H., advisor"
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Item Open Access A method for investigating avian predation on the adult Black Hills beetle(Colorado State University. Libraries, 1963) Stallcup, Patrick Lloyd, author; Baldwin, Paul H., advisor; Wygant, Noel D., committee member; Lechleitner, Robert R., committee memberProcedures for investigating avian predation on the adult Black Hills beetle, Dendroctonus ponderosae Hopkins, during the period off light and attack of this insect were developed and tested. Field work was conducted during the months of June, July, and August of 1961 and 1962 in two stands of ponderosa pine of about 50 acres each near Bailey, Park County, Colorado. The density of the population of beetles per 10 acres was computed from average number of beetles found in samples of infested bark. The relative intensity of beetles emerging and flying per day was determined from counts of beetles collected from cages installed on infested trees. Birds were censused along a census transect. The total area censused for each species was calculated and based on the greatest distance of recognition of birds which varied with density of forest and conspicuousness of each species of bird. The average number of birds per 10 acres was computed from 49 censuses taken throughout the summer. During the period of most intense emergence of the Black Hills beetle, birds were collected in an adjacent stand. The collected specimens were classified into feeding-categories and the stomach contents of each member of each category were examined for fragments of Black Hills beetles. Each feeding-category was analyzed as a single entity. The average proportion of fragments of beetles in the food of members of each feeding-category was estimated visually. These proportions were converted to equivalent weights that they constituted of the estimated weights of food consumed by these birds daily. These weights of fragments of beetles were converted to equivalent numbers of beetles. The average number of beetles eaten by members of each feeding-category during the period of most intense emergence of the beetle was computed. This computation was based on the number of birds of each feeding-category censused per 10 acres and the average number of beetles consumed by then. The proportion of the population of beetles consumed by birds was calculated to be 8.5 per cent. The 95 per cent confidence interval of this figure is from zero to 43.3 per cent. Field observations indicated that mortality of the Black Hills beetle during the previous winter was abnormally high. Considering this high winter mortality, the proportion of the population of beetles removed by birds was computed to be 11.6 per cent. The 95 per cent confidence interval on this figure is from zero to 59.5 per cent.Item Open Access Predatory and energetic relations of woodpeckers to the Engelmann spruce beetle(Colorado State University. Libraries, 1967) Koplin, James Ray, author; Baldwin, Paul H., advisor; Steinhoff, Harold W., committee member; Pettus, David, 1925-2014, committee member; Wygant, Noel D., 1908-, committee memberA general theory of the population dynamics of predator-prey systems was developed from a survey of pertinent literature. According to the theory, populations of simplified predator-prey systems fluctuate wildly and periodically. Complicating factors dampen the amplitude of the population fluctuations and thus exert a stabilizing influence on the systems. The predator-prey system between the Northern Three-toed, Hairy and Downy Woodpeckers, and the Engelmann spruce beetle was chosen for an investigation of the population dynamics of a natural predator-prey system. The population densities of several species of bark beetles attracted to trees killed and damaged by a fire on the study area in Northern Colorado, increased to levels that attracted the feeding attention of the woodpeckers. The numerical response of the woodpeckers to prey density was graded, that of the Northern Three-toed Woodpecker was the most pronounced and that of the Downy Woodpecker was the least pronounced. Spatial and temporal differences were noted in the foraging behavior of the three species of woodpeckers; similar but less apparent differences were also noted in the foraging behavior between the sexes of the Northern Three-toed and Hairy Woodpeckers. Both the interspecific and intersexual differences in foraging behavior were correlated with morphological and dietary differences. The metabolic demands of free-living woodpeckers were estimated by feeding diets of known caloric content to active woodpeckers in cages at several different ambient temperatures. Estimates were also made of the caloric content of Engelmann spruce beetle larvae and the rate at which they are digested by the woodpeckers. Combining these estimates with the estimates of the relative densities of woodpeckers, and the average number of spruce beetle larvae found per woodpecker stomach made it possible to calculate the number of larvae consumed by each species of woodpecker. This method gave results very similar to the usual method whereby the number of larvae surviving in bark protected from woodpeckers is compared with the number surviving in bark exposed to woodpeckers. Every aspect of the predator-prey system between woodpeckers and the Engelmann spruce beetle, except the number of larvae destroyed, conforms to general theory. The number of prey destroyed in this predator-prey system is higher than that known for any other system between vertebrate predators and invertebrate prey.