Species with different requirements can coexist if the environment varies in space; we therefore expect a positive relationship between species diversity and environmental heterogeneity. In this thesis I examine the influence of environmental structure on patterns of fern diversity in one hectare of old-growth forest and compare these patterns to other surveys covering a broad range of scales. The nineteen species recorded in the hectare had non-random spatial distributions and differed in their soil preferences. Diversity was positively related to soil moisture and negatively related to soil fertility, but there was no relationship with environmental variance. The counteracting influence of dispersal may predominate over selection processes at the hectare scale. Both species-area curves and the decreasing correlation of species composition with distance had very similar slopes over quadrat sizes ranging from 1 x 1 m to 50 x 50 km, suggesting that some diversity patterns may be independent of scale.

Diatoms have been proven to be reliable indicators of water quality in many countries of the world particularly Europe. The potential use of diatoms as indicators of water quality in South Africa was tested in the studies in this document. This study evaluates the potential use of diatom based indices by testing it against a macroinvertebrate index (SASS 5) and evaluating the variation in the index scores of the two indices due to changes in chemical water quality and habitat. It was concluded that the diatom monitoring system performs well as bioindicator of water quality. It was also concluded that it should be used as a complementary system to the much used SASS 5 invertebrate index. This conclusion was made due to the fact that diatoms react more directly to changes in water quality than macroinvertebrates (SASS 5), and macroinvertebrates react more readily to changes in habitat than diatoms. A further part of the study was to assess whether aut-ecological or diversity based diatom indices performed best in South African conditions. This study found that the ecological indices were more sensitive to changes in water quality than the diversity indices. The diatom based indices that performed best as water quality indicators were the specific pollution sensitivity index (SPI) and the biological diatom index (BDI). A standard method for the sampling, preparation and enumeration for diatoms to be used for index score generation is also suggested to ensure the comparability of diatom based index data to facilitate use of such bio monitoring data for management purposes. The main focus of the study was to eliminate some of the obstacles for the use of diatoms as bio indicators of water quality in South Africa. It is believe that this aim has been accomplished in the study. / Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2008.

Diatoms have been proven to be reliable indicators of water quality in many countries of the world particularly Europe. The potential use of diatoms as indicators of water quality in South Africa was tested in the studies in this document. This study evaluates the potential use of diatom based indices by testing it against a macroinvertebrate index (SASS 5) and evaluating the variation in the index scores of the two indices due to changes in chemical water quality and habitat. It was concluded that the diatom monitoring system performs well as bioindicator of water quality. It was also concluded that it should be used as a complementary system to the much used SASS 5 invertebrate index. This conclusion was made due to the fact that diatoms react more directly to changes in water quality than macroinvertebrates (SASS 5), and macroinvertebrates react more readily to changes in habitat than diatoms. A further part of the study was to assess whether aut-ecological or diversity based diatom indices performed best in South African conditions. This study found that the ecological indices were more sensitive to changes in water quality than the diversity indices. The diatom based indices that performed best as water quality indicators were the specific pollution sensitivity index (SPI) and the biological diatom index (BDI). A standard method for the sampling, preparation and enumeration for diatoms to be used for index score generation is also suggested to ensure the comparability of diatom based index data to facilitate use of such bio monitoring data for management purposes. The main focus of the study was to eliminate some of the obstacles for the use of diatoms as bio indicators of water quality in South Africa. It is believe that this aim has been accomplished in the study. / Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2008.

The diversity of Brachycera (Diptera) was studied in an old growth beech-sugar maple forest at Mont St. Hilaire, Quebec. Sampling was carried out weekly from early May to late September 2001 using a malaise trap, pan traps, a newly designed trunk trap and sweep netting. Almost 10,000 specimens from 45 families and over 334 species were collected. The most diverse families were Empididae (43 species), Tachinidae (39 species), Syrphidae (35 species) and Dolichopodidae (24 species). Collecting techniques were compared, with particular reference to the trunk trap designed for this study. NMDS ordination showed that a different Diptera assemblage was collected by each method. The greatest number of species was collected using the malaise trap; however, 21 species were collected only in trunk traps. Some of the most abundant species from trunk traps were collected rarely, or not at all, using other methods. These are species which are often considered rare in forests because they are infrequently collected using traditional techniques.

Alvars are naturally open habitats which are found in the Great Lakes region in North America and in Scandinavia. The insect fauna of four types of alvars (grassland, grassland savanna, shrubland and pavement) was sampled in the summer of 1996 on Manitoulin Island, Ontario. A total of 9791 specimens from four target insect groups (Coleoptera: Carabidae, Homoptera: Auchenorrhyncha, Hymenoptera: Symphyta and Lepidoptera: Papilionoidea and Hesperioidea) was identified. Results showed that the grassland savanna and grassland alvars supported the highest number of insect specimens whereas the pavement alvar supported the highest number of species. The origin of the fauna differed between the taxa depending on their closer association with specific microclimatic conditions (Carabidae) or on the presence of host plants (Auchenorrhynca). This first inventory of alvar insects in North America revealed the presence of a high number of species of interest to conservation (rare, disjunct or restricted species).

The diversity of saproxylic Cecidomyiidae (Diptera) associated with decaying logs was studied in an old-growth forest on Mont Saint-Hilaire, Quebec from June until September 2004. More than 24 000 specimens representing 323 species and morphospecies were collected in emergence traps set over American beech or sugar maple logs in two different stages of decay. The paedogenic species Miastor metraloas Meinert was by far the most numerous species with 17 002 individuals and was excluded from further analyses. Most of the remaining species were fungivores, detritivores or predators. Significantly more specimens were collected in logs in the more advanced decay stage, and indicator species analysis showed that the most abundant species were associated with this decay stage. Overall species richness was not significantly different between decay stages or tree species; however, non-metric multidimensional scaling indicated that the species assemblages associated with decay stage and tree species were significantly different despite the similar species richness.

The islands of the tropical South Pacific (TSP) are considered biodiversity hotspots. However, the biota of this region has received limited scientific attention and very little is known about its diversity, ecology and evolution. In this thesis we investigate some of the ecological and evolutionary processes in the TSP, focussing on lowland rain forests. We use molecular techniques to investigate evolutionary processes and vegetation surveys to study species diversity patterns and ecological processes. Chapter 1 reviews molecular, distributional and geographic evidence for dispersal versus vicariance explanations for the diversity and distribution of the TSP biota. Most islands of the TSP are geologically young (less than 40 million years old) and of oceanic origin, so most (if not all) of the biota on islands in the TSP arrived through long-distance dispersal events. This view is strongly corroborated by genetic data from published studies. Molecular studies also suggest two major source areas. One is located in the northwest, which includes Malesia and Southeast Asia, while the other is in the southwest and includes New Caledonia, Australia and New Zealand. We argue that local extinctions have occurred in source and stepping stone areas, creating sources of error for the interpretation of distribution and molecular data. In Chapter 2 we use allozyme data to investigate the question how Pacific cycads (Cycas, subsection Rumphiae) colonised the Pacific. We show that they colonised the Pacific and East Africa by long-distance dispersal, probably through floating seeds from a Malesian source area. Allozymes and morphological data provide support for two major groups within subsection Rumphiae and reveal close relationships between the extant species, suggesting very recent and/or ongoing dispersal events. Cycads are an example of recent diversification in a lineage with a long fossil record. The podocarp genus Dacrydium is another lineage with a long fossil record and in chapter 3 we investigate the colonisation and speciation processes in this lineage using allozymes and trnL-trnF plastid sequences. Our results suggest that the Pacific species of Dacrydium arrived recently (within the last 10 million years) in the TSP but are inconclusive about the source area of the genus. Combined molecular and ecological data suggest the occurrence of both allopatric and sympatric speciation in the Pacific radiation in this genus. Allozyme data also demonstrate the occurrence of hybridisation between two New Caledonian species. Our findings suggest that hybridisation and sympatric speciation may have played an important role in the evolution of the biota in the TSP. In chapter 4 we attempt to untangle the disparate forces driving alpha species diversity, forest structure and species composition in old-growth lowland tropical rainforest by assessing the tree species composition of twelve 1 ha vegetation count plots on 13 islands between New Guinea and Samoa. Using simplifications of a model based on biogeographic and ecological disturbance theory, we show that species diversity and richness are mainly influenced by size and area of an island, while endemism is mostly determined by isolation and area. High cyclone frequency is shown to increase the density of stems (with dbh > 10 cm). Correlations between the abundance of widespread canopy tree taxa and cyclone frequency suggest that cyclones affect species composition by increasing the abundance of cyclone-resistant species. However, floristic similarities show that geographic distance also affects species composition. It therefore appears that, for lowland rain forests in the TSP, biogeography is the major driver of species diversity and endemism and that disturbance is the major driver of forest structure, while both biogeography and disturbance affect the species composition. In chapter 5 we test the ability of NDVI (Normalised Difference Vegetation Index, a remotely sensed index of productivity) data and leaf samples as covariates of alpha species diversity using twelve vegetation count plots. NDVI performed poorly in estimating species diversity and species richness. However, the cost- and time-efficiency associated with remotely sensed data shows the potential of these methods, but only if accurate methods to estimate species richness are found. Species richness and species diversity estimates obtained from leaf litter samples correlate reasonably well with similar estimates obtained from count plots and are more than 30% cheaper and about 10% faster to obtain. If travel can be avoided through collaboration, leaf litter-based estimates of diversity could be obtained at about 5% the cost and in about half the time compared to count plots. Therefore the analysis of leaf litter is potentially a suitable and efficient method to obtain rapid estimates of species diversity in count plots. The final chapter discusses the roles of ecological and evolutionary processes in the TSP. While research to date has been scarce, especially on ecological processes acting on large scales, data show that the effects of ecology, evolution and biogeography are interlinked during the colonisation, establishment and subsequent evolution of taxa and biomes in the TSP.

Thesis (Ph.D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [135]-151).

Honors Project--Smith College, Northampton, Mass., 2010. / Includes bibliographical references (p. 18-21, 54-60).

Thesis (Ph. D. (Zoology and Entomology))--Rhodes University, 2005.