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- ItemOpen AccessAspects of the biology of the intertidal barnacle Tetraclita serrata Darwin in southern Africa(1987) Delafontaine, M TAn important area of research in biology deals with the integration of an organism with its environment. For a long time, interest was focused on the reactions of organisms to their physical milieu (Thiery, 1982). Subsequently, attention shifted to biological interactions such as competition and predation. More recently, biologists have come full circle in that physical aspects are, once again, being more fully investigated (e.g. Kazmierczak et al., 1985; Underwood, 1985). Shorelines provide an environment perhaps most ideally suited to such investigations. The transition zone between sea and land represents a unique mosaic of physical conditions whose diversity has yet to be fully explored by biologists. This is exemplified by classical models of species distributions involving 'wave action' (see Newell, 1979), a factor which is rarely precisely quantified in biological practice although its individual, hydrodynamic components have long been known to physical oceanographers. The present study of the biology of a rocky intertidal organism, th~ barnacl~ Tetraclita serrata Darwin, was carried out in southern Africa'between 1976 and 1984 with the specific aim of revealing the most important relationships between this organism and its physical milieu. The region is ideally suited for this purpose because a number of distinctly different climatic regimes occur along the South African coast. Thus, the cold-temperate western region is influenced predominantly by the cold Benguela Current (Fig. 1 ), whereas the warm Agulhas Current co.ntributes to the warmtemperate conditions on the south coast, merging into the subtropical environment of the east coast. In addition, an often rugged shoreline provides a multitude of microhabitats in which local physical conditions vary dramatically over very small distances.
- ItemOpen AccessAdolescent adjustment to parental divorce : an investigation from the theoretical perspective of structural family therapy(1985) Abelsohn, David Selwyn; Saayman, GrahamSignificant Aided-Unaided differences are also found: Aided families are perceived as more chaotic, disengaged, and enmeshed than Unaided families; Aided adolescents are characterized by more Externalizing (i.e . acting out) behavior problems than Unaided adolescents; and while all Unaided adolescents fall within the nonclinical normative range on the standardized test on Externalizing Problems, more than one third of Aided adolescents fall within the clinical range on this test. Further, significant differences in mothers' postseparation incomes are found between the Aided and Unaided groups, with the Aided being lower. Comparisons of the adjustment scores for the combined Aided plus Unaided groups with the test norms of the clinical and nonclinical standardization groups reveal that the adolescents as a group fall between the clinical and nonclinical norms, suggesting that divorce is a stressor for these adolescents which is within the realm of nonclinical, or nonsymptomatic, adaptation. These findings represent a first quantitative attempt with separated families to (a) demonstrate that individual adolescent adjustment is contingent on structural features of the family, and (b) differentiate in one study between characteristics of Aided and Unaided families and their adolescents. This is an important methodological issue which has not been controlled in previous studies. (iii) (2) Two qualitative clinical case studies demonstrate the pertinence of these family dimensions, both in understanding the plight of clinical postseparation families with adolescents and in guiding their treatment. The first family is characterized by disengagement and a collapsed Generational Hierarchy. The second family is characterized by rigid enmeshment and disengagement in the mother-son and father-son subsystems respectively. Finally , the family dimensions are employed to understand the successful efforts of a nonclinical , separated family with an adolescent to adapt over a 3- year period after the separation . As far as is known, these case studies are the first systematic attempt to apply these structural family concepts to postseparation families. Thus , the contribution of this thesis to our current understanding of the adjustment of adolescents to their parents' separation represents a first attempt to (a) quantitatively relate adolescent adjustment to structural dimensions of the family , and to differentiate between characteristics of Aided and Unaided families and their adolescents, and (b) qualitatively demonstrate the applicability of these structural dimensions in the clinical situation, and to understand the successful efforts of a nonclinical family to adapt after a separation.
- ItemOpen AccessDurability in male professional road cyclists(2023) Spragg, James; Swart, JeroenThe aim of this thesis was to investigate the phenomenon of durability in male professional road cyclists. Durability can be described as the ability to resist a fatigue-induced downward shift in the power duration relationship. Prior to this thesis, this phenomenon had been identified within the literature, however, it had not been systematically studied. Therefore, the primary aims of this thesis were to i) Synthesis the current research concerning durability and the fatigue-induced downward shift in the power duration relationship ii) Investigate whether methodological artefacts in the hitherto research were influencing the current understanding of durability iii) Assess whether durability is trainable and which modalities of training may be beneficial to improve durability iv) Investigate if the intensity of prior work influences durability and v) to investigate the potential underlying physiological determinants of durability. The final goal was to summarise and integrate these new research findings, and identify avenues for future research.
- ItemOpen AccessBiomineralization in loliginid squid statocysts and the use of statoliths to estimate age(1999) Durholtz, Marius Deon; Field, John; Cook, Peter; Lipinski, MarekThe use ofstatoliths to estimate the age ofloliginid squid is critically assessed. Alternating "light" and "dark" layers visible in statoliths viewed with a light microscope are proposed to reflect a daily cycle in statolith mineralization. A "light" and adjacent "dark" layer, known as an increment, are hypothesized to be deposited over a 24 hour period, and hence can be used to estimate the age of squid. Research was directed to the methodological aspects ofthe application ofthe statolith age estimation technique, as well as the physiological processes of statolith mineralization. A method ofpreparing statoliths of chokka squid Loligo vulgaris reynaudii for increment counting using light microscopy (LM) is described. The performance ofthe method is assessed by comparing the results with those obtained using scanning electron microscopy (SEM). The LM method is superior to the SEM method in that fewer specimens which require interpolation or extrapolation of increment numbers is obtained. For any given reader, the null hypothesis that increment counts obtained using LM were similar to those obtained using SEM could not be rejected. Either method can be used to count increments in chokka statoliths with similar effectiveness. Between-reader differences in increment interpretation and counting were apparent in the LM results, but not in SEM. The problem of interpretation ofstatolith microstructure may introduce a significant source oferror when using LM rather than SEM. The hypothesis that increments in squid statoliths are deposited with a daily frequency was tested for the first time in wild populations, using statolith marking experiments. The results are consistent with daily increment production in adult males of Loligo vulgaris reynaudii. The same result was obtained for the single adult female included in the study. Analysis of the errors involved in increment counting highlighted the importance of proper statolith preparation. The error in counting increments in a poorly prepared statolith may be three times higher than that in a well-prepared statolith. The results ofstatolith marking experiments conducted on Lo/igo vulgaris reynaudii in the laboratory were consistent with daily increment production in males, but not in females. Increment deposition rates in males were similar in both field and laboratory conditions, indicating that the results of laboratory experiments of this nature can be justifiably extrapolated to wild individuals. The hypothesis that temperature influences statolith growth and resultant microstructure was tested in a laboratory study ofthe loliginid squid Lolliguncula brevis. Groups ofsquid were subjected to various temperature regimes for extended periods, and the regions of the statolith deposited during the experiments were subsequently examined using laser scanning microscopy. Checks deposited in response to stressful events such as capture and handling are shown to consist ofa series ofprominent increments, rather than reflecting a period ofinterrupted statolith growth. Constant temperature conditions appeared to reduce increment contrast and clarity, presumably due to a dampening of the metabolic cycles associated with increment formation. Average statolith growth rates observed over the course of the experiment showed a strong positive relationship to ambient temperature. A significant sex effect was also apparent, with statoliths of female squid generally growing faster than those of males. Statolith Abstract Page 6 ABSTRACT The use ofstatoliths to estimate the age ofloliginid squid is critically assessed. Alternating "l ight" and "dark" layers visible in statoliths viewed with a light microscope are proposed to renect a daily cycle in statolith mineralization. A "light" and adjacen t "dark" layer, known as an increment, ate hypothesized to be deposited over a 24 hour period, and hence can be used to estimate ihe age of squid. Research was directed to the methodologica l aspects of tile application of the statolith age estimation technique, as well as the physiological processes of statolith minera lization. A method of preparing statoliths ofchokka squid Loligo vulgaris reynaudiifor increment counting using light microscopy (LM) is described. The perfonnance of the method is assessed by comparing the results with those obtained using scanning electro
- ItemOpen AccessChange in secondary school geography education: teacher attitudes and practice(1987) Ballantyne, Roy; Cook, G.; Spargo, P.