http://hdl.handle.net/1957/17094 2013-05-26T00:51:27Z 2013-05-26T00:51:27Z Woltering, Daniel Mark http://hdl.handle.net/1957/17991 2011-03-24T07:09:19Z 1976-04-09T00:00:00Z

Predator-prey interactions under the influence of ammonia Woltering, Daniel Mark Predator-prey interactions, as measured by the consumption and growth rates of a predator (Micropterus salmoides) and by the observed activities of both predator and prey (Gambusia affinis), were found to be sensitive to sublethal levels of ammonium chloride (reported as unionized ammonia NH₃). One bass and 15, 30, 60 or 120 mosquitofish were placed in each of 13 150 liter aquaria, designed with uniform cover for the prey, and allowed to interact for ten days. These prey densities were maintained by restocking every 24 hours, thus providing a wide range of food availability for the predators. Experiments were first run without adding ammonium chloride in order to establish baseline responses of both predators and prey. The system was then exposed to a range of toxicant concentrations from 0.13 mg/l to 0.86 mg/1 NH₃. Responses of predators and prey were measured and compared to the baseline data. Consumption and growth rates of the unexposed bass increased with increasing prey densities. Consumption rates ranged from one to ten percent of mean dry weight of bass per day, growth rates from a loss of two percent to a gain of three and one-half percent of mean dry weight of bass per day. Exposure to low levels of NH₃ had no observable effect on the interactions. When exposed to toxicant concentrations higher than 0.34 mg/l NH₃, substantial decreases in consumption and growth rates were found for bass in experiments with prey densities above 15. These deviations from the baseline correlated well with prey density in that the effects were greatest at high prey densities where the bass were being continuously harassed by the mosquitofish. The utility of this type of bioassay approach to aquatic pollution is discussed. Graduation date: 1976

1976-04-09T00:00:00Z Liss, William J. http://hdl.handle.net/1957/17990 2011-03-24T07:09:19Z 1974-03-11T00:00:00Z

The dynamics of exploited guppy populations exposed to dieldrin Liss, William J. Sixteen populations of guppies (Poecilia reticulata) were established in laboratory aquariums. Eight populations were exposed to dieldrin at a mean concentration of 0.525 ppb in the water and 2.11 ppm in the food, tubificid worms. Eight populations received control water and food. All populations were fed three grams of tubificid worms per day. Exploitation rates of 0.60, 0.45, 0.30, and 0.15 were selected. Each rate was assigned to two control populations and two populations exposed to dieldrin. All fish except the young (less than nine millimeters) in each population were exploited at their designated rate according to a systematic exploitation schedule every 28 days. All populations were exploited fifteen times. The number of fish in the exploited phase of populations exploited at 0.60 remained stable during most of the experiment. Populations exposed to dieldrin maintained a greater number of fish than control populations through increased recruitment. Apparently, dieldrin reduced the cannibalistic behavior of adult guppies and allowed more young to survive to recruitment size. The biomass and yield in weight of control populations and populations exposed to dieldrin was similar. Increased recruitment in populations exposed to dieldrin was therefore compensated by reduced growth. Reductions in recruitment resulting from increased cannibalism on young fish caused the number of fish in the exploited phase of populations exploited at 0. 45, 0. 30, and 0. 15 to decline. Populations exposed to dieldrin maintained the same number of fish and followed the same trends as control populations. These populations maintained a high density of adult fish and intraspecific competition for food may have overcome the tendency of dieldrin to reduce cannibalistic behavior. Although population number declined, the biomass and yield in weight of these populations remained stable. Reductions in recruitment had not yet caused a major decline in the number of adults and may have been compensated by increased fish growth. As population number declined, the average length and weight of the catch increased. Populations exploited at 0. 45, 0. 30, and 0. 15 were apparently beginning to undergo periodic cycles. Mean equilibrium yield in weight declined as exploitation rate was reduced. Yield in weight of each population was located on the descending limb of a surplus-yield curve. Age, growth, production, and yield in weight of females in populations exploited at 0.60, 0. 45, and 0.30 were determined from the length-frequency distributions of the catch. At each exploitation rate, during the younger age classes, when the production of a cohort of females was greater than its yield, the biomass of the cohort increased. During the older age classes, when yield became greater than production, the biomass of the cohort declined. As exploitation rate increased, the mean individual weight of each age class and the relative growth rate of fish of a particular weight also increased. Increased growth enabled fish from high exploitation rates to maintain greater production and yield than fish from low exploitation rates. Graduation date: 1974

1974-03-11T00:00:00Z Bull, Evelyn L. http://hdl.handle.net/1957/17989 2011-03-24T07:09:20Z 1975-02-24T00:00:00Z

Habitat utilization of the pileated woodpecker, Blue Mountains, Oregon Bull, Evelyn L. In the spring and summer of 1973 and 1974 a study of habitat utilization by pileated woodpeckers (DryocoPus pileatus picinus) was conducted on the Starkey Experimental Forest and Range in the Blue Mountains of northeastern Oregon. Pileated woodpeckers are dependent on a forest habitat for feeding and nesting. The alteration of this habitat through intensive timber management is detrimental to the species, particularly because of the elimination of dead wood, both standing and downed. Nests were excavated in large ( >58 cm dbh), tall (>12m), ponderosa pine (Pinus ponderosa) and larch (Larix occidentalis) snags in areas with mean densities of 494 stems and 50 snags per ha. These nest trees were in forest sites containing the highest densities of stems and snags found on the study area. Pileated woodpeckers fed primarily in dead wood in snags, logs, and naturally created stumps. Feeding occurred in a variety of tree species of various sizes and physical characteristics. Forest sites containing the highest densities of stems and snags on the study area were preferred by the pileated woodpecker for feeding. In 1974, there were at least 13 pairs of pileated woodpeckers on the 11,400 ha study area. This translated to 665 ha of forested habitat per pair. During spring and summer, nesting territories were estimated at 250 to 500 ha. The critical components in pileated woodpecker habitat are: snags, particularly large snags, logs, large trees, diseased trees, dense timber, and high densities of snags. The requisite attributes of size, density, and decadent trees are most common in mature uncut forests. These elements can be maintained at a satisfactory level with moderate modifications of current forest management practices. Graduation date: 1975

1975-02-24T00:00:00Z Thompson, Bruce Carlyle http://hdl.handle.net/1957/17988 2011-03-24T07:09:19Z 1976-05-04T00:00:00Z

Evaluation of wire fences for control of coyote depredations Thompson, Bruce Carlyle See pdf Graduation date: 1976

1976-05-04T00:00:00Z