This project was aimed at (i) characterizing and comparing littoral fish communities upstream and downstream of the Moses-Saunders hydroelectric dam on the St. Lawrence River near Cornwall, Ontario and Massena, New York and (ii) exploring relationships between habitat characteristics (including depth gradient--the distance from shore to a 1m depth, percent aquatic vegetation, and percent substrate type) and fish community characteristics (diversity, abundance and biomass). A total of 74,419 fish (43 species) were captured in 36 sites (14 upstream and 22 downstream) using a standard sampling protocol in 1994 and 1995. The downstream region (western portion of Lake St. Francis) had significantly higher number of fish species and biomass when compared to the upstream reservoir (Lake St. Lawrence). A clustering analysis of a Jaccard similarity matrix based on the presence-absence of species for each site revealed largely distinct interregional fish community composition with relatively homogeneous intra-regional communities. A principal component analysis (PCA) of fish species caught in 60% or more of sites allowed the definition of the main fish assemblages. The downstream fish community was characterized by a high abundance of Notropis volucellus, Fundulus diaphanus and Notemigonus crysoleucas, where as upstream a high abundance of Pimephales notatus was found. A PCA of habitat variables revealed a dispersal of downstream sites throughout the graph. The upstream sites clustered together. This suggests a broad spectrum of habitat types downstream, while upstream is more homogeneous. Regression and correlation analyses found relationships between fish variables and habitat variables. The downstream area had a wider variety of habitat types, as well as the higher percentage of vegetation cover, boulder and gravel, which supported a more diverse and abundant fish community.

The forest tent caterpillar (Malacosoma disstria Hubner) is a serious economic pest of many deciduous trees throughout North America. This insect avoids the foliage of red maple (Acer rubrum L.). An investigation of the phytochemical activity of the foliage of A. rubrum against the forest tent caterpillar (FTC) was undertaken. It was discovered that the foliage of sugar maple (Acer saccharum Marsh.), generally considered to be a food host of the FTC, could also contain secondary chemicals that harm this insect. When fed foliage of both maples, the FTC grew at a significantly reduced rate than those larvae that were fed the foliage of the preferred host, trembling aspen (Populus tremuloides Michx). All larvae fed red maple were dead within two weeks. The primary mode of action of sugar maple was one of internal toxicity (growth inhibition) whereas red maple was severely antifeedant and possibly also internally toxic. Feeding bioassays with extracts and purified compounds from the maples incorporated into artificial diet at sub-ecological levels, revealed that both species are chronically toxic and cause concentration-dependent reductions in larval growth and pupal weight, and increases in larval mortality. An increase in the time needed to reach pupation and adulthood for males in the red maple treatment was also observed. The extract of A. saccharum leaves was actually more active against the forest tent caterpillar than was the species of maple that the insect always avoided. A study of the variability of the maple defensive phytochemicals showed that although some variation in anti-FTC activity between different growing sites and within individual trees from the same growing site existed, it was not great enough to support the hypothesis that certain sugar maple trees possessed relatively lesser phytochemical defenses. (Abstract shortened by UMI.)

<p> The home range can be further understood by examining: (1) environmental factors that are responsible for its selection, and (2) habitat use. Green turtle (<i>Chelonia mydas</i>) home ranges are characterized by their food abundance, distribution, and quality. The shallow water habitats of The Bahamas are important foraging sites for juvenile green turtle. The goal of this study was to determine how turtles use their home range at a tidal foraging site. I tracked turtle home range using acoustic telemetry. I conducted esophageal lavage on tracked turtles and mapped the vegetation coverage. Turtle home ranges were small, and often overlapping areas (mean &plusmn; SD= 0.64 &plusmn; 0.24 km²). Turtles consumed primarily seagrass (<i>Thalassia testudinum</i>), which was concentrated inside the tidal creek. This study documented the smallest recorded home ranges of juvenile green turtles and examines the combination of the effects of tide, temperature, and vegetation on green turtle home range.</p>

Species richness is an ecologically important descriptor of ecosystems and, as a component of biodiversity, may be useful for conservation planning. Global and local patterns of richness have been related, with moderate success, to climatic and habitat parameters respectively. However our ability to predict species richness breaks down at intermediate scales (quadrats 10$\sp0$-10$\sp3$ km$\sp2$ in size extending over regions of 10$\sp3$-10$\sp6$ km$\sp2$). We examined the spatial variation in breeding bird species richness in 100 km$\sp2$ squares, across 200,000 km$\sp2$ of southern Ontario, and tested for relationships with a suite of environmental variables that included, climate, human population, land cover, a heterogeneity index, soil fertility and parkland. We conclude that at this spatial scale, the variation in total avian species richness over southern Ontario is not sufficiently well related to either temperature or habitat to warrant further investigation of possible mechanistic links. The richness of certain guilds, however, shows some promise as a possible measure for conservation planning and management. (Abstract shortened by UMI.)

Over the past 15 years a great deal of literature has been generated in an attempt to understand the regulation of trophic level biomass and size structure in aquatic systems. I tested the hypotheses that the among-lake variability in biomass and size structure of planktivorous fish, zooplankton, and phytoplankton communities depends on: (1) resource availability (bottom-up processes); (2) piscivorous sport fish stocking (top-down processes); and (3) the particular species of piscivorous sport fish stocked. We sampled 31 lakes in southeastern Ontario over the summers of 1993 and 1994 to obtain indices of abundance, biomass, and size structure of the planktivorous fish, zooplankton, and phytoplankton communities. Seven of the lakes were not stocked and the remaining 24 had stocking intensities ranging from 30 to 1500 individuals stocked per hectare over the 6 years prior to sampling. For both bottom-up and top-down analyses, trophic interactions were strongest at the base of the food web and weakened at higher levels, becoming non-significant thereafter. From these results I conclude that: (1) piscivorous sport fish stocking as a whole (at least at the magnitude examined here) had no effect on planktivorous fish, zooplankton, and phytoplankton biomass or size structure; (2) rainbow trout (Oncorhynchus mykiss) stocked lakes differ at the zooplankton and phytoplankton level from lakes stocked with other species of piscivore; (3) trophic interactions are most evident at the base of the food web (at the zooplankton and phytoplankton level); and (4) resource control (especially total phosphorus) of biomass and size structure in aquatic communities is much more important than consumer control, and it is limited to the phytoplankton and zooplankton. Our results suggest that stocking with piscivorous fish (as practised for sport fishing purposes) does not effectively manipulate plankton abundance. (Abstract shortened by UMI.)

The St Lawrence River, near Cornwall, Ontario and Massena, New York, was declared an Area of Concern (AOC) by the International Joint Commission in 1985 due to high levels of contaminants in physical and biological components of the environment. A Remedial Action Plan (RAP) was established to identify specific problems and implement remedial measures. As part of the RAP process, the public at large was consulted and one of the identified concerns was the extent of mercury and PCB contamination of bottom sediments. We assess the evidence for local origin of mercury and PCB sediment contamination by looking at the spatial relationships between suspected point sources and spatial gradients in sediment contaminant levels. The results strongly suggest that the Domtar and Courtauld's outfalls are (were) important local sources of mercury. Similarly, there is strong evidence that the Grass River (ALCOA), Reynold's and G.M. as a group comprise an important local source of PCBs. We examine spatial correlations between mercury and PCB concentrations in sediments and a small nearshore planktivore, the Spottail Shiner (Notropis hudsonius). (Abstract shortened by UMI.)

It has been hypothesized that the trophic structure of aquatic ecosystems is controlled by two sets of processes, often referred to as bottom-up and top-down. The bottom-up hypothesis postulates that nutrient limitation, and various physical-chemical factors directly or indirectly regulate the biomass and community structure of organisms at all levels of the food web. The top-down hypothesis postulates that predation by upper levels of the food web (specifically piscivorous fish) strongly influence the biomass, community size structure and productivity of organisms in the lower trophic categories. In this study we attempt to determine the strength of both bottom-up and top-down control on lower trophic level biomass and community size structure, in lakes of varying trophic status. During summer stratification, 29 temperate lakes of varying trophic status and fish species composition were sampled in Quebec and Ontario. This study found a strong relationship between nutrient availability and phytoplankton biomass, and between nutrient availability and zooplankton size structure. Bottom-up effects were quite strong at both the phytoplankton and zooplankton levels. Neither piscivorous fish presence nor indices of piscivorous fish abundance had a detectable effect on most indices of phytoplankton and zooplankton biomass and community size structure. Only cladoceran biomass and the variance in individual dry weight were higher in lakes where piscivorous fish were present. Piscivorous fish predation-effects were not evident at the phytoplankton level and were relatively weak at the zooplankton level. Total zooplankton biomass, crustacean biomass and cladoceran biomass were significant in explaining residual variation in the TP-Chl a model and improved this model's predictive ability by 24%, 18% and 22%, respectively. This study found that the effect of piscivorous fish did not depend on the concentration of total phosphorus in the 29 lakes. No evidence of interaction between trophic status and predation was determined. (Abstract shortened by UMI.)

Logging influences the distribution and abundance of breeding birds by changing the structure and composition of forests. In particular, very little old-growth forest remains. Studies suggest that the structural characteristics of old-growth forests of the Pacific Northwest provide habitat not available in younger forests. This study compared certain characteristics of habitat structure, and abundance of selected bird species in three forest types in the Temagami region of northern Ontario: (i) old-growth pine forests (no history of catastrophic disturbance) (ii) mature pine forests (undisturbed for approx. 100 years) (iii) managed forests (previously pine-dominated and selectively-logged approx. 50 years ago). Canopy height, tree species diversity and percent cover of vegetation in the upper canopy, average number of vegetation layers and spatial variability in the number of layers were all significantly greater in old-growth than in managed or mature forests. Abundances of some bird species were significantly correlated with habitat characteristics. However, none of the bird species censused were significantly more abundant solely in old-growth forests. Our results suggest that vegetation characteristics predict bird abundance more strongly than forest type.

The residual variability surrounding chlorophyll a---total phosphorus (Chl-TP) relationships decreases the predictive ability of phosphorus loading models to forecast algal biomass production in lakes. In the first section of this thesis I attempt to account for the residual variation in chlorophyll a concentration by examining how the sequestration of phosphorus into non-algal compartments of the water column varies among aquatic biomes. This is achieved by examining the relationships between chlorophyll a and various chemical forms (particulate, soluble, organic and inorganic) and size classes (total, >64mum, 30--64mum, 3--30mum, 0.2--3mum) of phosphorus. In the second section, I examine if the much lower than expected chlorophyll yield of Prince Edward Island (PEI) estuaries is the result of mussel grazing and/or increased turbidity or if it is the result of a general regional effect caused by the Island's geological characteristics. This latter hypothesis implies that PEI lakes and rivers would also possess lower chlorophyll yields. This question is examined by comparing the data from each of the PEI biomes (lakes, rivers, estuaries) with that of reference set possessing the expected chlorophyll a to total phosphorus ratio. (Abstract shortened by UMI.)

General opinion in the contemporary literature is that disturbance strongly influences patterns of species diversity, and that diversity is greatest at intermediate levels of disturbance. However, empirical evidence is equivocal, and quantitative predictions about the strength of diversity-disturbance relationships are lacking. Using Markov models of dynamics of real communities, I derived predicted changes in diversity when communities are subjected to quantified disturbance gradients. I also derived predictions regarding effects of sampling intensity and species selectivity of disturbance on diversity-disturbance relationships. My models predict peaked relationships should be relatively rare, variation in diversity over disturbance gradients typically should be low, and relationship shape varies with sampling intensity. These results are broadly consistent with a review of published diversity-disturbance relationships. A meta-analysis of 197 published diversity-disturbance relationships was performed to determine how frequently observed relationships are peaked; how strong, in general, relationships are; and whether various attributes of a study influence the observed shape and strength of a relationship. Non-significant relationships were the most common, and peaked responses were reported in only 16% of cases. Variation in diversity explained by disturbance was variable, but averaged ∼50%. Results suggest that strong and/or peaked relationships may arise from procedural artifacts. I conclude that there is little evidence to support the belief that disturbance should have a consistently important role in determining patterns of diversity, or that diversity-disturbance relationships are typically peaked. Anthropogenic habitat loss is often cited as the most important cause of recent species' extinctions. Recent studies identifying hot spots of imperiled species have suggested that habitat loss is the primary factor threatening the survival of imperiled species. However, interpretation of such hot spots is not practical without knowledge of where imperiled species have been lost. I determined distributions of richness and losses of imperiled species in Canada, and statistically examined the relationship between species' losses and various landuse variables. Several hot spots of losses were identified in southern regions of Canada. The combination of frequent and intensive insecticide applications, routine herbicide use, and habitat loss due to agricultural development appears to be the most important threat to imperiled species.