Thesis (M.S.)--University of Delaware, 2008. / Principal faculty advisor: Timothy E. Targett, College of Marine & Earth Studies. Includes bibliographical references.

Thesis (Honors)--College of William and Mary, 2009. / Includes bibliographical references (leaves 42-43). Also available via the World Wide Web.

Thesis (Honors)--College of William and Mary, 2009. / Includes bibliographical references (leaf 64). Also available via the World Wide Web.

Thesis (M.S.)--University of Montana, 2007. / Title from title screen. Description based on contents viewed June 12, 2007. Includes bibliographical references (p. ix-xv).

We address the problem of the consistency between discrete and continuous models for density-dependent size-structured populations. Some earlier works have discussed the consistency of density independent age and size-structured models. Although the issue of consistency between these models has raised interest in recent years, it has not been discussed in depth, perhaps because of the non-linear nature of the equations involved. We construct a numerical scheme of the continuous model and show that the transition matrix of this scheme has the form of the standard discrete model. The construction is based on the theory of Upwind Numerical Schemes for non-Linear Hyperbolic Conservation Laws with one important difference, that we do have a non-linear source at the boundary; interestingly, this case has not been explored in depth from the purely mathematical point of view. We prove the consistency, non-linear stability and hence convergence of the numerical scheme which guarantee that both models yield results that are completely consistent with each other. Several examples are worked out: a simple linear age-structured problem, a density-independent size-structured problem and a non-linear size-structured problem. These examples confirm the convergence just proven theoretically. An ample revision of relevant biological and computational literature is also presented and used to establish realistic restrictions on the objects under consideration and to prepare significant examples to illustrate our points.

The distribution and abundance of six bumblebee species (Bombus) and their associated flowers were studies for 12 weeks in 26 discrete subalpine meadows over the summer of 1981. Principal component analysis of flower densities identified phenological patterns of blooming and differential affinities of plants for moisture as the major contributors to flower variation among the meadows. A positive relationship between bumblebee species diversity and meadow area in the early summer and mark-recapture experiments suggested that queens are attracted to large meadows for nest establishment. After colony initiation meadow floristics govern Bombus species diversity and abundance. Results showed that: (1) mid- to late-summer bumblebee diversity, the temporal occurrence of new queens, and the densities of two species were correlated with the density of nectar producing flowers; (2) flower composition in meadows where local extinctions of at least one Bombus species occurred differed from those where all species persisted; and (3) the number of species reaching reproductive fruition was independent of bumblebee species composition. These results underscore the importance of nectar resources in Bombus colony and guild development. Multiple regression analyses were used to relate the effects of meadow size, elevation, and floristics to observed densities of Bombus flavifrons and B. rufocinctus. In mid- to late summer a significant portion of the variation in densities not explained by these variables was accounted for by densities of congenerics. In meadows where all Bombus were removed except B. flavifrons or B. rufocinctus significant positive density compensation was observed for the latter, but not the former. These results are suggestive of relationships among bumblebee densities, intensity of competition, colony ontogeny, colony reproduction, and local floristics that question both the (1) simplistic views of Bombus guild organization based on the paradigm of tongue length, corolla depth, and character displacement; and (2) the stochastic view that flowering phenologies and developmental time lags thwart resource-based guild organization.

No description available.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Masters of Science June 2015 / Adenium swazicum is currently listed as Critically Endangered due to past and future population declines, which have been estimated to be 80% over three generations. Although 10-20% of the population is present in formal protected areas, no studies have been published on the species population biology and ecology, which are essential to ensure its effective conservation. The broad aim of this research was to investigate the population biology and ecology of Adenium swazicum by investigating factors such as current distribution, population structure, reproductive characteristics, germination, herbivory and current threats. The current distribution of Adenium swazicum was determined by searching all herbarium records on the National Herbarium Pretoria Computerised Information System as well as additional suitable habitat through fieldwork, conducted during the flowering period (October to April) between 2009 and 2011. The current Extent of Occurrence (EOO) and Area of Occupancy (AOO) were determined by incorporating all confirmed localities of Adenium swazicum. To determine the population biology of Adenium swazicum, fifty plants in four representative populations were studied with regards to plant size, extent and intensity of herbivory, flower production as well as follicle and seed production. The reproduction of Adenium swazicum was determined through pollinator observations while the number of flowers and fruit (follicles) produced, as well as fruit and seed set were compared in the four representative populations. Seed viability was determined through tetrazolium staining, while germination experiments were used to determine minimum, maximum and optimum temperature ranges as well as mean germination time. Seedling emergence and establishment were determined for various soil media, depth of seed planting, watering regimes and shading. The current distribution of A. swazicum included 23 localities in South Africa, Swaziland and Mozambique, while the Extent of Occurrence (EOO) was approximately 8 392km² (839 246 ha) and the Area of Occupancy (AOO) was estimated to be 8.5km² (850ha). Although this indicates that A. swazicum might be more widespread than previously believed, the population sizes were all small (between 1 and 141) and most of the populations were still threatened, mostly by habitat destruction and harvesting for medicinal purposes. The research found that adult A. swazicum plants were found to have a high tolerance to natural disturbance (fire, herbivory) and resprout from the underground tuber even if all above ground parts were destroyed. It is however unlikely that seedlings and juveniles will be able to withstand significant impact on the above ground parts since the underground tuber only develops in plants older than 24 months. Despite big and bright floral displays which should attract insect pollinators, low diurnal insect activity was observed around A. swazicum. However, a fast flying Sphingidae (Hawk Moth), which is most likely a pollinator, was observed at A. swazicum flowers at dusk. Small population size and isolation might have been the cause of no reproduction (very few follicles and no seed) in at least one population in 2010. Continued reproduction failure as well as destruction of remaining adult plants by housing developments and collection for medicinal purposes might lead to the local extinction of this population. With sufficient available moisture, high germination success (82 to 90%) for A. swazicum was achieved at temperatures between 20°C and 35°C, without any pre-treatment, and ‘maximum’ germination was reached in less than 90 hours. The cultivation of A. swazicum from seed is highly successful, with different soil media having no apparent influence on seedling emergence and establishment. Seedling emergence was highly dependent on water, and although shading did not influence seedling emergence, seedling establishment/survival was highly dependent on shading. Since seed release from A. swazicum coincides with the start of the rainy season (October), as well as short germination responses, it is highly unlikely that A. swazicum forms persistent soil seed banks. The uncomplicated propagation of A. swazicum has resulted in a significant ex situ collection at the Lowveld National Botanical Garden, with more than 2000 plants (adults and seedlings) grown from seeds which were collected from four different populations over an eight year period. In addition, the Skukuza indigenous nursery in Kruger National Park has more than 250 plants (adults and seedlings) all of which were grown from seed collected in the KNP. These living ex situ collections provide a valuable source of plant material for future restoration projects. Despite an increase in the number of known Adenium swazicum populations, the population sizes are small (1 to 141) and most populations are still threatened by habitat destruction and high levels of exploitation by medicinal plant harvesters. It is therefore recommended that Adenium swazicum remains listed as Critically Endangered (A4acd;B2cb). Criteria A4acd: “An observed, estimated, inferred, projected or suspected population reduction (up to a maximum of 100 years) where the time period must include both the past and future, and where the causes of reduction may not have ceased or, may not be understood, or may not be reversible based on”. This assessment was based on (a) the causes of reduction of Adenium swazicum populations have not ceased and may not be reversible, (c) there is a decline in AOO, EOO and habitat quality; and (d) there is actual, continuing exploitation of A. swazicum. Adenium swazicum also qualifies as CR under criteria B2b(iv,v): “Geographic range in the form of Area of Occupancy (AOO) of <10km² with (b) continuing decline in (iv) number of locations or subpopulations and (v) number of mature individuals”. No immediate management intervention is needed for populations which are located in formal protected areas, although it is recommended that these populations be monitored, especially with regards to reproduction to inform future management decisions. It is possible that low seed viability recorded in population C in 2009 and 2010 could be due to inbreeding depression caused by the destruction of surrounding populations due to sugarcane fields and harvesting of adult plants for medicinal uses. The Low veld National Botanical Garden had collected parental material from populations surrounding population C since 2003; it is recommended that restoration of decimated populations be conducted in secure areas on for example private land and community schools. Lastly, seed collected from various populations should be banked at the Kew Millennium Seed Bank Project, England to ensure viable ex situ collections.

The hard tick Ixodes ricinus is one of the most important species of disease vectors worldwide. It transmits a variety of pathogens, including spirochaetes that are the causative agent of Lyme borreliosis (LB) in humans. This study aimed at analysing different aspects of the ecology, molecular evolution, and microbial associations of I. ricinus. A novel scheme for the phylogenetic analysis and genotyping of I. ricinus was established as part of this study. Phylogeographic clustering of I. ricinus samples fromdifferent European countries was observed, while samples from two different sites inSouthwest England did not show spatial differentiation. The ecology and host abundance in these two habitats was assessed. Differences in the density of questing ticks and in the abundance of rodent hosts were observed. Both sites exhibited low densities of rodents and of ticks infesting them. A blood meal analysis revealed high proportions of mixed feedings and showed artiodactyls to be a main host group for immature I. ricinus ticks from Britain. The prevalence rates of Wolbachia endobacteria in British I. ricinus samples were higher than rates found in samples from other European countries. The unique endosymbiont Midichloria was detected in all female I. ricinus ticks that were screened. A newly developed multi gene analysis of Midichloria samples from six European countries showed a largely coordinated phylogeography with their tick hosts. Taken together, the findings of this thesis demonstrate that British I. ricinus ticks differ from their European counterparts in several ways, which has implications for the epidemiology of infectious diseases transmitted by this vector.

Various physical and biological factors affecting annual productivity in a Red-tailed Hawk population in north-central Oregon were investigated. The percentage of the population successfully fledging one or more young was the most important factor in determining the number of young fledged per pair in a given year. Neither clutch size nor the number of young fledged per successful nest varied significantly. Percent pair success was correlated with several January weather variables. A cold and dry January is positively correlated with Red-tailed Hawk productivity. This is apparently related to the onset of rapid vegetative growth and this in turn is positively correlated with the timing of the emergence and reproductive cycle of the principal prey, Belding’s and Townsend's ground squirrels, (Turner 1972). Because a cold and dry January delays the emergence of ground squirrels, the period of emergence and dispersal of the young squirrels more closely corresponds to the time of peak food needs of the young Red-tailed Hawks, and greater pair success is observed. This relative abundance of prey appears to be of greater importance than actual abundance. Red-tailed Hawk productivity was found to correlate significantly with two habitat variables & the presence of adequate numbers of dispersed hunting perches and relative ground squirrel abundance. The presence of one or more perches per sixteenth section provided the best single correlation. Neither territory size nor competition from interspecifically territorial Swainson's Hawks were correlated with productivity of Red-tailed Hawk territories. Red-tailed Hawks with inhabited dwellings within their territories fledged significantly more young than those without.