The population dynamics of Microtus townsendii in a linear habitat were monitored weekly for one year (June, 1971-August, 1972). Demographic characteristics such as location on study area, sex, weight (age), reproductive condition, and survival were recorded weekly. An Intensive study of early Juvenile survival was also undertaken. The population was observed to decline in the spring of 1972 from peak densities the previous summer and early spring. The decline did not appear to result from decreased reproductive effort or dispersal, but could be explained solely on the basis of mortality. Several observations were made which did not follow the usual demographic trends in microtine population biology. Extremely high densities with small home ranges for individuals were found on the linear study area as compared with areas of continuous habitat. This population became sexually mature at much lower body weights than other populations of Microtus townsendii in the area and average body weights were lower, although growth rates were comparable. / Science, Faculty of / Zoology, Department of / Graduate

The three general body armour forms of Gasterosteus aculeatus (Linnaeus), high, intermediate and low plate count forms, are found in nonbreeding marine populations. In breeding season initially the population in the nontidal portion of Bonsall Creek consisted of the low and intermediate plate count forms. Later when the tidal zone was occupied by breeding sticklebacks all three body armour forms were present and from the limit of the tidal influence the low and intermediate forms became less frequent seaward. In Chase Creek there exists an anadromous breeding population but there was no adjoining freshwater population. In Chase Creek however there did exist a zone where all three body armour form were present. Therefore, the development of the pattern of plate variation in the creek's tidal zone does not appear to be dependent upon the presence of both freshwater and marine population tyrjes. In Bonsall Creek where both a freshwater and a marine population bred, low plate count individuals from the freshwater zone and high plate count individuals from the adjoining tidal zone were reciprocally transferred in wire baskets. Mortalities of transferred fish were shown to be significantly higher than those of the controls indicating a possible barrier to gene exchange between the two populations. However, the presence of the intermediate plate count form in the freshwater zone of Bonsall creek strongly implicates gene flow between these two groups of fishes. all three forms collected from the tidal zone of Chase Creek. Showed the same mortality rate when placed in freshwater. This suggests that the low and intermediate plate count fish breeding in the tidal portion of Chase Creek were of marine origin. Ten morphological characters were combined in a discriminant function and used to classify breeding individuals from Bonsall Creek. The discriminant function showed a gradual change in morphology of the fish distributed from marine to freshwater. It is concluded that while there was considerable differentiation between adjoining freshwater and anadromous breeding populations of Gasterosteus aculeatus, no evidence of a morphological discontinuity as would be expected of separate species. However, the presences of the hybrid form in the freshwater zone of Bonsall Creek strongly implicates gene flow between those freshwater and marine groups of fish. Eleven populations ranging geographically from the Alaska Peninsula to Chehalis Biver in Washington State were similarly subject to discriminant function analysis. These samples did not show clinal variation in their scores, though the scores of the populations were significantly different suggesting local adaptation and possible restriction of gene flow within the marine environment. / Science, Faculty of / Zoology, Department of / Graduate

This project was designed to study the patterns of variability in fish populations. My hypothesis is that specific population patterns should be related to evolutionary concepts (phylogenetic patterns} , zoogeographic considerations (faunal patterns), and their vertical distributions. These patterns should be detected by comparing certain population parameters [growth parameters (K, LINF), the natural mortality coefficient (M) size at first maturity (LM), age at first maturity (TM), size at age 1 (L1) , the weight-length exponential coefficient (b) , and life span (T95)] which are intrinsic biological features of the population. Comparative methods were used to analyze data from published fish population studies by comparing fish population parameters, individually, in pairs (ratio or linear regression), or grouped together (discriminant analysis or Cooley and Lohnes' classification method), in order to find the similarities or differences among different categories, and then to group these into patterns. Published data provided 682 parameter records from 43 families (171 species) of fishes. My findings suggested that more satisfactory results would be obtained from a greater volume of data. Therefore, all the analyses were based mainly on 15 families with large sample sizes (Bothidae, Clupeidae, Cyprinidae, Engraulidae, Gadidae, Hiodontidae, Osmeridae, Percidae, Pleuronectidae, Salmonidae, Sciaenidae, Scombridae, Scorpaenidae, Sparidae, and Sgualidae). Sample sizes, mean values, standard errors, and coefficients of variation for population parameters and relative characters of the 15 families of fishes are listed in the summary table. These data would enable the extrapolation of results based on many areas for management of other fish stocks where data are lacking. In the majority of families significant linear regression relationships were found between 1/K--LINF, between LM--LINF, and between M--K. This means that fish having a greater asymptotic length (LINF) also have a larger size at first maturity (LM), a lower natural mortality coefficient (M), and a lower rate (K) at which the asymptotic length is reached. Using the F-test and the appropriate t-test as a basis for comparison of variances and means of individual parameters, it is evident that in most cases there are significant differences between families. This confirms one of my hypothesis; namely that differences between families, as shown by population parameters, exist from phylogenetic considerations. By comparing the four characters (K, LINF, LM, and LH/LINF) the fish families can be divided into the following groups: A) Shoaling pelagic fishes - Engraulidae, Clupeidae, and Osmeridae. These families have the highest K values (1.6 for Engraulidae, over 0.4 for the others), the smallest LINF, LM, and a very high LM/LINF ratio (over 0.7). B) Large pelagic fishes - Scombridae. This family has a moderately high K value (around 0.35) and the largest LINF. C) Demersal fishes - Gadidae, Pleuronectidae, Scorpaenidae, Sparidae etc. These families have low K values (less than 0.25), intermediate LINF size, and lower LM/LINF ratios (less than 0.6). D) Freshwater fish - Cyprinidae. This family has K and LINF values which are similar to those of the demersal fishes, but has a smaller LM length and, especially, the lowest LK/LINF (0.4) and TH/T95 (0.2) ratios. Stepwise discriminant analysis based on 7 variables in the 15 families showed that over 90% of the 620 cases considered independently could be correctly classified into the right families. Cooley and Lohnes' classification method was also utilized among species within 5 major families (Clupeidae, Cyprinidae, Gadidae, Pleuronectidae, and Scombridae). Correct classification ranged from 5 8.6% (Pleuronectidae) to 87.6% (Cyprinidae). These results further confirmed the existence of population patterns by examination of population parameters. Cluster analysis based on 7 population parameters displayed the closeness among the 15 families. Dendrograph relationships brought out the ecological, rather than the systematic, affinities between families. / Science, Faculty of / Zoology, Department of / Graduate

The prediction of the performance of hybrid plants as production material is complicated by the genetic structure of the hybrid population. Fundamental quantitative genetic concepts are defined with respect to disomic, randomly fertilized populations which are in linkage and Hardy-Weinberg equilibrium. Hybrid populations of crosses are, however, in disequilibrium and do not meet these assumptions of quantitative genetic theory. The theory of inheritance in hybrid populations has not been fully developed and the complex models that have been developed have not reached a stage where they have been implemented to adapt selection practices for hybrid populations. Therefore in practice hybrids are often selected using selection methodology that has been developed for pure species despite large differences in the underlying genetic properties of the populations. It is not known to which extent such selections are able to predict the performance of progeny or clones in hybrid populations. This study was based on historical data and investigated the efficiency of BLUP in hybrid populations. As a case study the selection of ortets in three hybrid Eucalyptus populations was investigated. Ortet selection in E. grandis × E. saligna, E. grandis × E. urophyllaand E. grandis × E. camaldulensis populations was compared with selection in E. grandis populations. Clonal performance was predicted from a series of hybrid family trials whereas realised clonal performance was assessed in clonal trials. The predicted and realised clonal performances were correlated to assess the efficiency of the predictions. A series of constructed indices was created that placed a range of weights on family versus individual tree performances to obtain an indication of the range of correlations that could be expected from the data. Different BLUP methods were compared including selection for breeding and various forward selections for clonal forestry (“clonal forward selection”). The clonal forward selections were based on different estimates of the proportion of total genetic variance that is ascribed to non-additive genetic variance. The results of the study indicated that there were no observable differences in the efficiency of the BLUP predictions in the studied hybrids in comparison to prediction in E. grandis There was, however, a decrease in the correlations between predicted and realised clonal performances with increasing genetic distance between the parents. Furthermore, the genetic values were better predictors of clonal performance than breeding values and genetic values which were based on higher assumptions of non-additive genetic variances (37% of total genetic variance) were more efficient than those based on assumptions of lower proportions (20%). This study indicates that BLUP methods may be efficient in predicting the clonal performance in the three hybrid populations that were investigated. Copyright / Dissertation (MSc)--University of Pretoria, 2009. / Genetics / unrestricted

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In this dissertation, we develop a new type of prior distribution, specifically for populations themselves, which we denote the Dirichlet Spacing prior. This prior solves a specific problem that arises when attempting to create synthetic populations from a known subset: the unfortunate reality that assuming independence between population members means that every synthetic population will be essentially the same. This is a problem because any model which only yields one result (several very similar results), when we have very incomplete information, is fundamentally flawed. We motivate our need for this new class of priors using Agent-based Models, though this prior could be used in any situation requiring synthetic populations. / Doctor of Philosophy / Typically, statisticians work with parametric distributions governing independent observations. However, sometimes operating under the assumption of independence severely limits us. We motivate the move away from independent sampling via the scope of Agent-based Modeling (ABM), where full populations are needed. The assumption of independence, when applied to synthesizing populations, leads to unwanted results; specifically, all synthetic populations generated from the sample sample data are essentially the same. As statisticians, this is clearly problematic because given only a small subset of the population, we clearly do not know what the population looks like, and thus any model which always gives the same answer is fundamentally flawed. We fix this problem by utilizing a new class of distributions which we call spacing priors, which allow us to create synthetic populations of individuals which are not independent of each other.

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