Browsing by Author "Tipton, Alan R."
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- Breeding bird populations in relation to the vegetation structure of abandoned contour mines in Southwest VirginiaChapman, David L. (Virginia Polytechnic Institute and State University, 1977)Twelve study areas on abandoned contour mines in southwest Virginia were surveyed to investigate relationships between breeding bird population parameters and structural aspects of the disturbed area vegetation. The territorial mapping method was employed to census bird populations. The number of breeding species, number of breeding pairs, bird species diversity, and number of observed species (breeding or visiting) were determined for each disturbed area, the marginal undisturbed forest, and each total study area (marginal and disturbed areas combined). Vegetation was sampled within units of similar vegetation on each disturbed area; 17 vegetation parameters were recorded for each unit. These were weighted by the size of each vegetation unit and averaged for each disturbed area. Linear and multiple regressions of each population variable were performed on 51 vegetation and site-factor variables. Bird population parameters of the disturbed and total study areas showed positive relationships with several aspects of disturbed area revegetation. However, among forested orphan mines, decreases in bird populations were observed when canopy closure apparently affected a reduction in understory vegetation. Bird populations of the marginal areas decreased with the reforestation of the disturbed areas, apparently reflecting a decrease in the edge effect. Several sets of equations for population parameters of the disturbed and total study areas are presented for use in habitat evaluation. Relationships revealed for bird population parameters of the disturbed and total study areas suggest that reclamation efforts should strive to achieve a high degree of vegetative cover, increase the amount of ground layer vegetation, and provide for the future development of higher vegetational strata. These vegetational features should be introduced in a manner which will augment existing vegetational heterogeneity.
- A General Population Dynamics Theory for Largemouth BassJester, Douglas B. Jr.; Garling, Donald L. Jr.; Tipton, Alan R.; Lackey, Robert T. (Virginia Tech. Division of Forestry and Wildlife Resources, 1977)In this report, we develop a general theory of the relationship between life history and population structure for largemouth bass. In its most usable form the model is represented by a stochastic integral equation that is analogous to the classical Lotka model for age structure of populations. The corresponding differential equations can also be used successfully when closed-form solutions are available or when the phenotype dimension is low enough to permit numerical solution. Three general conclusions are presented. First, population dynamics may be appropriately viewed as a consequence of life history phenomena. This view suggests that, at least where prediction of population structure or where explanation of the phenomena is desired, such phenomena as density-dependence may be most appropriately described by analyzing effects of population structure and density on life history in the population. The second conclusion is that variation in life history may be important in determining population structure. Terms describing effects of variation are explicitly included in the model equations. The magnitude of these terms, however, is completely unknown for any life histories with which we are familiar. The third conclusion to be drawn is that population structure, at least averaged over time, should be fairly stable in large populations. Effects of variation in small populations, on the other hand, have not been analyzed and might be important.
- A general population dynamics theory for largemouth bass fisheriesJester, Douglas B. Jr. (Virginia Polytechnic Institute and State University, 1977)Resolution of the main issues in largemouth bass management will require the ability to predict the effects of exploitation on population structure, optimally select size limits, relate bass population structure to prey population structure, and predict the effects of fluctuations in recruitment on production and yield. A general model of population structure was developed for use in studying these problems. The model was derived by examining the relationship between life history and population structure. Life history processes are described as mixed continuous and jump stochastic processes. The model was derived in two forms, an integro-differential equation and a stochastic integral equation, which include all of the classical continuous-time population models as special cases. Two general results concerning the model were proven. First, the stochastic integral equation was shown to predict the same expected population structure as a deterministic model using average birth and death rates whenever the processes are uncorrelated. However, it is very unlikely that birth rate, death rate, and density will be independent, so the stochastic and deterministic models will generally diverge. Second, it was shown that with density-independence the expected population structure in the stochastic model is asymptotically stable. Special cases of the model were used to illustrate the possible effects of exploitation on average catchability and population structure. Methods for calculation of optimal length limits and production and yield were illustrated for simple cases. Use of the full power of the model, however, must await more detailed description of factors influencing mortality and growth, especially the effect of the density and size structure of available prey.
- A Qualitative Analysis of The Southern Pine Beetle's Wildlife ImpactMaine, John D.; Leuschner, William A.; Tipton, Alan R. (Virginia Tech. Division of Forestry and Wildlife Resources, 1980)Wildlife's social value has long been known. Early attempts to place dollar values on wildlife were crude (Stains and Barkalow, 1951; Collins, 1959) and often incomprehensible. For example, Collins found that each deer killed by bow hunters was worth $5,280 based on hunter expenditures. However, these early researchers were aware that it is important to consider wildlife's social value in forest management decisions. These include pest management dee is ions generally and Southern Pine Beetle ( Dendroctonus frontal is Zimm) (SPB) management decisions specifically. Wildlife has three basic values in the Southeast: recreational, aesthetic, and scientific. The recreational value is realized by the more than 30 million people who spend billions of dollars each year pursuing fish and game species. These people partially support the sporting arms and ammunition, camping equipment, campground, and restaurant industries.
- A test of the variable nature of density-dependent mortality in fish populationsBernard, David R. (Virginia Tech, 1978-11-18)Veracity of past analyses on the impact of impingement and entrainment of fish in power-plant cooling systems was questioned. Density-dependent dynamics were hypothesized as variable, not constant, making previous analyses based on constant density-dependent or density-independent mortality in error. This hypothesis was tested with a simulation model based on complex biological and behavioral mechanisms for individual fish, thereby forgoing the need for assuming the kind of mortality exhibited by a fish community prior to the analysis. Yellow perch and walleye in Oneida Lake, New York, were focal points of this test, and data taken in 1972 from Oneida Lake were used to validate the model. Model experiments consisted of varying turbidity, water temperature, impingement and entrainment, and abundance of young perch and walleye. Under most conditions in the experiments, individual growth was unchanged, and predators maintained a high frequency of full stomachs. Exceptions were that water temperature influenced growth and that adult walleyes went hungry when fry of both species were limnetic. Mortality of young perch proved depensatory and that of young walleye density-independent. Mortality of walleye fry was inversely influenced by abundance of young perch. High levels of turbidity greatly enhanced fry survival for both species. Impingement and entrainment reduced survival of young perch and young walleye by 43 and 30 percent, respectively. Expected losses due to density-independent impingement and entrainment were 3 and 2 percent. Depletion of young perch occurred because of their depensatory mortality; depletion of young walleye occurred because their survival was related to abundance of young perch. High abundance of young perch and high turbidity dropped mortality to density~independent levels of about 3 percent. These mitigating effects of turbidity and high abundance showed that mortality could shift from density-dependent to density-independent dynamics. The relationship between abundance of young perch and mortality of young walleye meant that no analysis based on a single species could properly assess impacts of impingement and entrainment in Oneida Lake. The conclusion was that density-dependent and density-independent mortality are variable and are influenced by certain conditions: 1) compensatory mortality is based on density-dependent growth, 2) density-~independent and depensatory mortality are based on density-independent growth, 3) density-independent mortality occurs when predation removes insignificant numbers of prey, and 4) depensatory mortality occurs when predators remove large numbers of prey.
- Utilization of natural nest sites by Eastern Bluebirds in southwestern VirginiaPierson, Thomas A. (Virginia Tech, 1978-11-05)Eastern Bluebirds (Sialis sialis) were found to be utilizing natural nest sites in the vicinity of Blacksburg, Virginia, during 1976 and 1977. Forty-seven natural nest sites, 37 in fencepost cavities and ten in tree cavities were discovered by driving roads in rural areas, scanning fencerows and utility wires with binoculars, and by searching fencerows on foot. Ninety-one percent of nest cavities used by bluebirds were made by woodpeckers. Height of cavity entrance, entrance diameter, and distance from entrance to cavity bottom were best able to distinguish anong bluebird fencepost nest cavities, nest demonstration display sites, and Starling (Sturnus vulgaris) fencepost nest cavities, using discriminant function analysis. Four nest cavities used by bluebirds in 1976 were no longer available in 1977 due to the replacement of fenceposts and tree limb breakage. No new cavities in fenceposts were observed being excavated by woodpeckers.