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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Die rol van dieldrin in waterbesoedeling met spesiale verwysing na die invloed daarvan op varswaterfauna

Van Jaarsveld, Jan Harm 11 February 2014 (has links)
D.Sc. / Please refer to full text to view abstract
32

The role of meiofauna in the benthic community of a small oligotrophic lake

Hoebel, Michael January 1978 (has links)
Meiofaunal distribution and abundance were studied in Marion Lake, a small, shallow (8m maximum) oligotrophic lake in southwestern British Columbia. Experimental techniques were used to investigate the influence of food and predation on meiofaunal populations, and to estimate relative carbon -flow to all components (micro-, meio-, and macrofauna) of the zoobenthic community. In two years' sampling of over 50 species of meiofaunal rotifers, nematodes, copepods, cladocerans and halacarine mites, only a few species were abundant. Three depth zones were sampled (1.0, 2.5, 4.5m) and maximum densities occurred at 2.5m. Population densities of all groups were stable over the sampling period, fluctuating less than one order of magnitude annually. In culture studies, representative meiofaunal species had longer generation times and lower reproductive rates than expected. Attempts to use laboratory results to predict field population dynamics were generally unsuccessful, but led to clarification of reproductive parameter estimates. Experiments in the laboratory and in the field suggested that meiofaunal species are not food-limited. Predation on meiofauna is not heavy but might be significant for those species whose reproduction is suppressed by adverse temperatures. Radiotracer experiments indicated that carbon flow to the zoobenthic community from sediment microflora was partitioned approximately 12% to microfauna (ciliates), 12% to meiofauna, and 76% to macrofauna, while the contributions to zoobenthic biomass were 1%, 7% and 92% respectively. In related experiments, a common harpacticoid copepod species had a high assimilation efficiency but rapidly respired and excreted recently ingested carbon. Meiofaunal organisms are apparently not an important food source for higher trophic levels in Marion Lake but may play a significant role in stimulating microfloral production by their grazing activity. / Science, Faculty of / Zoology, Department of / Graduate
33

Patterns of animal abundance in lakes : the role of competition in the fish-macroinvertebrate relationship

Hanson, John Mark, 1955- January 1985 (has links)
No description available.
34

Distributional analysis of the freshwater mussel fauna of the Tennessee River system, with special reference to possible limiting effects of siltation

Dennis, Sally D. January 1984 (has links)
Mussel studies in the Tennessee River drainage (1973 - 1982) examined ecology and distribution and investigated factors limiting to distribution. This river system presently supports 71 freshwater mussel species, 25% of which are endemic to the Cumberlandian Region. Species have been extirpated from this drainage within the past 60 years, however the number of extant species remains high. The major impact of man's activities has been reduction of available habitat. Past and present distribution records indicate that mussel species assemblages are determined by geologic history and stream size. Although some overlap of species exists among stream size categories, there is no longer a continuous gradation from one category to the next; mussels exist in isolated communities separated by nonproductive river reaches. Productive reaches supporting more than 60 mussel species once existed in habitats spanning the transition from medium to large rivers; reaches now altered by impoundment. The maximum number of species reported in recent collections from any one site in the Tennessee drainage is less than 40, which seems to be the maximum number of species niches available. Quantitative sampling reveals characteristic patterns of species dominance. Changes in species dominance and age class structure provide a better basis for evaluating changes over time than do species composition or diversity alone. Mussel density was found to be more variable than species composition, and was unrelated to species abundance. Experiments on effects of siltation indicated that silt can be a significant limiting factor to mussel distribution. Transplant studies showed that mussels transplanted into heavily silted areas exhibited poor survival over a one year period compared to mussels moved to unsilted habitats. Results indicate that siltation may interfere with reproductive activity. Laboratory experiments testing the effect of suspended silt on the uptake of C-14 tagged algae by freshwater mussels showed that suspended silt can interfere with feeding. Food uptake was reduced to approximately 50% (of control) at silt levels of 211 to 820 mg/l, and to 80% at silt levels over 1000 mg/l. It was concluded that the limiting mechanism is one of dilution of food rather than direct interference with filtration or respiration. / Ph. D.
35

A comparative sampling study of benthic invertebrate populations in a prairie stream

Petersen, Gene Leslie. January 1979 (has links)
Call number: LD2668 .T4 1979 P48 / Master of Science
36

Distribution, production, and utilization of the benthic macroinvertebrate fauna of Imperial Reservoir on the lower Colorado River, Yuma County, Arizona

Boyle, Terence Patrick. January 1979 (has links)
Data for a study of the benthic macroinvertebrates in Imperial Reservoir in Yuma County, Arizona was collected 1970-1973. Imperial Reservoir is an old, heavily sedimented reservoir on the lower Colorado River. An extensive dredging program revealed that the benthic habitat supported a low number of invertebrate species (four insects and two oligochaets) in comparison to other bodies of water. Probable reasons for the low number of species included high salinity, low organic detrital input into the reservoir, low habitat and substrate diversity, temporary low dissolved oxygen concentration, possible contamination with agricultural chemicals, and the remoteness of Imperial Reservoir from other aquatic environments. Within Imperial Reservoir the benthic macroinvertebrate community was restricted to more isolated, calm, side lakes which altogether made up only 23% of the entire surface area of the reservoir. Within these side lakes benthic macroinvertebrates were found primarily on mud substrate. Invertebrates were not found beneath dense stands of Najas marina, a rooted submersed macrophyte. Only two species of invertebrates appear to inhabit rocky substrates. Community analysis suggested that there were no large differences among most habitats where benthic invertebrates were found. A study of the microdistribution of each species of invertebrate indicated that there were two patterns of spatial dispersion: (1) taxa which bred continuously appeared to have no life history related change in dispersion; and (2) taxa which formed recognizable cohorts appeared to spread out from initial egg mass and dispersion changed with time from clumped to random. Secondary net production measures were made directly on predominant benthic invertebrates at two sites in Imperial Reservoir. Both sites had similar production values which were low when compared to production values from other bodies of water. Low benthic production in Imperial Reservoir was related to several environmental factors including high water temperature and temporary low oxygen concentration near the bottom during the summer, low input of organic detritus into the reservoir, and high predation on benthic invertebrates by fish. Collection and analysis of the stomach contents of the bass, bluegill and redear sunfish revealed that the smaller fish of a species were more dependent on benthic invertebrates for food. Large bass did not use benthic invertebrates as heavily as either bluegill or redear.
37

The Vertical Stratification of the Macrobenthos in the Brazos River, Texas

Poole, Walton Charles 12 1900 (has links)
Quantification of stream macrobenthos populations has remained a perplexing problem in rivbrine ecology, despite numerous attempts at improvement. This is in part due to well documented variations in chemical and physical parameters locally and geographically, and resultant adapted macrobenthos populations. Southwood (1968) and Hynes (1970a) have reviewed the various sampling techniques developed'for the census of lotic macrobenthos populations. Needham and Usinger (1956), Chutter (1969), and others have pointed out the difficulty in obtaining adequate numbers of samples which will yield population estimates with desired statistical confidence, and still maintain some degree of sampling economy. Needham and Usinger (1956) and Gaufin et al. (1956) mentioned the "patchy" distribution of aquatic insect populations as the primary source of this difficulty. The concept of patchy distribution in insect populations was originally discussed by Andrewartha (1961). Attempts to improve confidence through improved sampling devices and techniques have led to development of numerous types of samplers. Cummins (1962) indicated that there were almost as many samplers as there were researchers.
38

Studies on the ichthyo-fauna in Plover Cove Reservoir : with special reference to Tilapia mossambica (Peters).

Man, Shek-hay, Hanson. January 1974 (has links)
Thesis (M. Phil.)--University of Hong Kong, 1974. / Offset from typescript.
39

The macroinvertebrate community of vernal pools in southwestern Québec /

Doran, Bruce R. January 1999 (has links)
Temporary snowmelt pool ecosystems in southwestern Quebec were examined with special emphasis on identifying the macrofauna and determining their spatial distribution, as well as ascertaining temporal changes in community composition. 68 taxa were collected from ten snowmelt pools. Major taxa represented were Diptera, Coleoptera, Hemiptera, Trichoptera, Odonata, Ephemeroptera, Anostraca, Isopoda, Amphipoda, Gastropoda and Bivalvia; the insects dominated the communities and the Culicidae (Diptera) was the most abundant taxon collected. The fauna were unevenly distributed both spatially and temporally amongst the pools. The occurrence of taxa was similar in pools in the same geographic location. The habitat characteristics of each pool, coupled with their proximity to a permanent waterbody and their accessibility to organisms, perhaps influenced the distribution of the various taxa. A successional pattern was observed in which filter-feeders and detritivores appeared first, followed by predators. After drought, a similar pattern was seen in pools that were replenished by summer rains, but taxon diversity was lower. In addition, pools with longer hydroperiods harboured more taxa than shorter-lived pools.
40

The trophic ecology and macrofauna of Kahana Estuary, Oahu

Timbol, Amadeo Sembrano January 1972 (has links)
Typescript. / Bibliography: leaves [208]-221. / xix,, 221 leaves illus., maps, tables 28 cm

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