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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Population Limitation of Jackrabbits: an Examination of the Food Hypothesis

Clark, William R. 01 May 1979 (has links)
The study was conducted to examine the importance of forage resources in limiting peak population density of black-tailed jackrabbits (Lepus californicus). The research design combined field studies of jackrabbit diet and vegetation impact with computer simulation of herbivore nutrition and population dynamics. The relationships between available forage, dietary intake, energy and protein balance and population changes were compared for high and low population density. Hypotheses tested were : (1) Dietary composition is unaffected by availability above 10 kg/ha; (2) Jackrabbits do not require more forage than is available at high population densities; (3) Dietary composition is not significantly different at high and low densities; (4) Dietary composition is not significantly different between sexes; (5) Nutritional balance of lactating females is not significantly altered at high density; and (6) Nutritional balance of females entering the breeding season is not significantly altered at high density. The field studies were designed to measure dietary preference by the jackrabbits, the availability of herbage, and utilization of selected plant species. Jackrabbits ate nearly all forage types available but primarily consumed dominant shrubs in fall and winter, suffrute scents in fall and winter, grasses in spring and summer, and forbs in summer. There was no significant difference between dietary composition or preference rating among density periods or sexes. Dietary percentage of preferred forage species was directly related to availability above 10 kg/ha. Jackrabbits removed an average of 30 to 40 percent of individual plants of Kochia americana, but only browsed on 5 toll percent of all available plants. Total removal of Kochiastanding crop averaged only 3.7 percent. The model used in the simulation studies incorporated relationships involving existence, activity and production (growth, gestation and lactation) requirements to estimate forage requirements. Intake and requirements affect energy and protein balance which are related to body weight changes and production. Model mortality rates are modified by nutritional deficiency as a fraction of the requirements. The following conclusions resulted from model simulations. Forage requirements are less than 1 percent of available forage, even at high population density. Nutritional balance of lactating females was unaffected by observed diets or population density. Nutritional balance of females entering the breeding season is unaffected by diet but may be affected by early breeding date or large litter sfze. Individual nutritional response and its interaction with food does not cause significant change in population mortality rates. Nutritional deficiency may contribute to mortality, particularly during lactation or winter periods, but these effects are independent of population density.
12

Effects of Sublethal, Cerebral X-Irradiation on Movement and Home-Range Patterns of Black-Tailed Jackrabbits

Nelson, Lewis, Jr. 01 May 1970 (has links)
Effects of sublethal, cerebral irradiation on movement and home-range patterns of black-tailed jackrabbits were studied in Curlew Valley, Utah, using radio-telemetry. Irradiation of 70 captive animals indicated that the LD50(30) was between 5,556 and 6,200 roentgens. Nine wild, free-living experimentals were trapped in desert terrain, irradiated, transmittered, and released at the capture sites. Seven wild controls were treated similarly but were not irradiated. The field-irradiation dosage was 5,000 roentgens. Tracking accuracy was determined by telemetering transmitters at fixed locations. Mean hourly movement was measured within 20-30 percent error and home ranges were measured with an error of less than 22 percent. Experimentals had a mean hourly movement of 1,176,8 feet and controls 980.0 feet, significantly different at the .05 probability level. Experimentals had a bimodal activity curve with peaks at 5:00 p.m. and 3:00 to 5:00 or 6:00 a.m. Controls displayed no such pattern. Experimentals had a mean, daily home range of 66.1 acres and controls 34,1 acres, significantly different at the .05 probability level. Experimentals had a seasonal home range of 279.0 acres and controls 247.0 acres, not significantly different at the .05 probability level. A probability index showing the frequency distribution of each animal's activity within 300-foot concentric, circular bands around a geometric center of activity showed similar distributions for both groups. The greatest concentrations of activity were within the innermost band for each group but experimentals had a slightly greater scatter of points in the outermost zone. These distributions were not significantly different at the .05 probability level. Sublethal, cerebral irradiation appears to have increased activity levels of experimental animals but not changed those home-range characteristics involving the total area occupied and tenacity of site attachment. This increased activity may have resulted from inhibitory areas in the cortex which permitted greater expression of activity from the limbic system.
13

Impact of the Black-Tailed Jackrabbits (Lepus Californicus) On Vegetation in Curlew Valley, Northern Utah

Westoby, Mark 01 May 1973 (has links)
The interrelations of black- tailed jackrabbits and the desertshrub vegetation on which they were feeding were studied in Curlew Valley, Northern Utah. The vegetation was described as a threecornered continuum, the corners being types dominated respectively by Artemisia tridentata, Atriplex ~ onfertifolia, and Sarcobatus vermiculatus. Jackrabbit diet was studied by microscopic analysis of plant fragments in stomachs from shot animals. The method was inaccurate, apparently because the ratio of identifiable tissues to all ingested tissues was very low, and varied between plant taxa, and seasonally. This problem seems intractable for desert shrub vegetation. The diet was similar to that reported by other workers on this species, with perennial grasses and forbs most important in sprlng and summer, shrubs in autumn and win ter. Features new to this vegetat ion were large percentages of Halogeton glomeratus, particularly in autumn and winter, and intense selection for Kochia americana. Attempts to explain the foods chosen ln terms of t heir nutrient contents were partically successful. Diet selection by large generalist herbivores was conceptualized as optimization of nutrient intake, mediated by long-delay learning, and constrained by food availability only at very low levels of availaoility. Spatial variation in jackrabbit diets confirmed this "cut-offll response to ava i 1 all i 1 i ty . Percentage utilization was estimated indirectly as jackrabbit density, times yearly food consumption per jackrabbit, times yearround percentage of each taxon in the diet, div i ded by available biomass of each taxon. Less abundant plants were more intensely used, which is expected if consumption does not vary continuously with availability. Perennial grasses, Kochia americana and possibly Grayia spinosa seemed to be under damaging pressure at high jackrabbit densities. Kochia had almost disappeared from outside a sheep- and jackrabbitproof exclosure since the 1950 1 s. In other exc1osures, the presence or absence of jackrabbits seemed to make no difference to the rate of vegetation recovery over 5-7 years after exclusion of sheep. Jackrabbit use of a crested wheatgrass seeding was concentrated ln a 300 m band around its edge.

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