Inaug.-diss.--Heidelberg. / Lebenslauf. "Literatur-nachweis": p. [43]-46.

The object of this study was to test the influence of benthic invertebrate drift in a stream on the benthic standing crop; whether it operated only as an agent for removal of surplus organisms from the standing crop or in a more indiscriminate manner, leading to depletion of these organisms in upstream areas. It was hypothesised that drift acts as a benthic population regulator and therefore would not influence a standing crop at optimum density. This was tested by comparing standing crop changes in two sections at a small stream differing in numbers of drift predators, coho salmon underyearlings ( Oncorhynchus kisutch (Walbaum) ), and steelhead trout underyearlings and juveniles (Salmo gairdnerii Richardson). It was found that these two salmonid species derived a significant proportion of their diet from groups of invertebrates which frequently occur in the drift. It is inferred therefore that predation by the fish contributed to observed differences in drift abundance between areas with high and low fish population density. However, it was not possible to quantify the consumption of drift accurately because it could not be determined whether an organism found in the stomach of a fish came from the drift or directly from the benthos. It was assumed that all means of accrual and removal of organisms to and from the standing crop other than drift and predation by salmonids were equal in the two stream sections. Benthic standing crop measurements showed no differences in density between stream sections that could be attributed to the drift difference. It was expected that some decrease would have resulted in the high fish density section relative to the low density section as more direct predation on the benthos would have occured in that section. It was found, however, that the standing crop increased in the high fish density section relative to the low fish density section, suggesting a greater influence on the standing crop by the unmeasured factors of accrual and removal than the measured drift and predation factors. / Science, Faculty of / Zoology, Department of / Graduate

Dissertation (PhD)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Thesis (M. Phil.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 147-156).

Thesis (M.S. in environmental science)--Washington State University, December 2008. / Title from PDF title page (viewed on Mar. 4, 2009). "School of Earth and Environmental Science." Includes bibliographical references (p. 24-27).

Thesis (Ph. D.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 200-243).

Speciation, the division of one species into two, has provided evolutionary biologists with a rich ensemble of questions, conundrums and revelations for over a century, and yet our understanding of many of the factors affecting this complex, multidimensional process remains limited. In this thesis, I aimed to further our understanding of speciation using divergent populations of three-spined stickleback (Gasterosteus aculeatus) on the island of North Uist, Scottish Western Isles. Firstly, I explored the degree of morphological and genetic separation between three stickleback ecotypes, showing that both strongly reproductively isolated, and admixed populations exist in close proximity. I then attempted to identify the ecological and genetic origins of strongly isolated species-pairs, testing two competing explanations for their existence. I showed that a recent 'double-invasion' is unlikely, but found stark differences in the long-term genetic history between ecotypes, indicating that the evolution of species-pairs may be related to secondary contact between anciently diverged mitochondrial lineages. I then conducted mate choice trials to assess mating preferences between ecotypes, and to test for reinforcement in species-pairs. Consistent with the idea that speciation in this case is not driven purely by ecological factors, I found no evidence that reinforcement drives assortative mating in species-pairs. Rather, it appears that extant mating preferences have developed as a by-product of other adaptations. Finally, I took a brief interlude to document and investigate an exciting chance finding, internally developed embryos retained within the ovaries of a normally oviparous species, before concluding by summing up my findings, their relevance for scientific progress, and avenues opened up for further research.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1984. / Includes bibliographical references (p. 451-473).

Inaug.-diss.--Basel. / At head of title: Aus der zoologischen anstalt der Universität Basel. Vita. "Literatur-verzeichnis": p. 145-149.

Not available / text