The Great Lakes has been impaired by elevated concentrations of contaminants, and different regulatory actions are taken to decrease theses concentrations. Recent research of Dr. Azim suggests a decline in mercury levels in the Lake Erie, and an increase in the Hg concentration in the fish communities. This research is a follow up study to examine whether the contaminant levels are indeed increasing. In the first chapter we evaluate the temporal trends of polychlorinated biphenyls (PCBs) in Lake Erie fish over the last 30 years by conducting the Exponential and Dynamic Linear Modeling analysis. DLM analysis in the chapter two detects the PCB and Hg contaminant trends in a broader range. There is a high variability in two contaminants trends. These patterns may be because of factors such as fish physiological parameters, and the impact of invasive species. The results of my research will contribute to the Toxics Reduction Strategy.

The Allen Paradox is the observation that, in aquatic communities, there is insufficient prey production to support predator growth. An assessment of the literature reveals that this paradox remains apparent in one of every four studies. Here, a novel explanation for this paradox is proposed: predators that feed in a spatially-heterogeneous-prey environment (SHPE) may experience a greater net energy gain than in a corresponding uniform-prey environment (UPE), meaning that predators may require less food than has been traditionally perceived. A model was developed to simulate a predator’s energy gain while feeding in a SHPE rather than a UPE. According to the simulation, a greater net energy gain in a SHPE than a UPE is possible, but only under certain conditions. Since prey can be utilized more efficiently in a SHPE, a given amount of prey production can supply more predator growth, which can have positive implications in fish stocking.

Although considerable research has been invested in disentangling the factors limiting species’ ranges at local and continental spatial scales, less attention has been granted to the relationship between species’ spatial distributions and landscape attributes at intermediate spatial scales. This research investigates the spatial relationship between avian species’ distributions (Ontario Breeding Bird Atlas [2001-2005] data) and landcover heterogeneity (Ontario Land Cover [1991-1998] data) in terms of their respective boundary locations (i.e., high rates of change in landcover composition and avian species turnover) in a vulnerable transitional zone in southern Ontario. Significant spatial overlap was found between landcover and avian boundaries. Given that land management decisions are most often made at the regional or landscape scales, this positive spatial relationship has important implications for conservation efforts. Future research should focus on assessing the spatial relationship between landcover heterogeneity and avian species’ distributions for different functional and taxonomic groups.

The Great Lakes has been impaired by elevated concentrations of contaminants, and different regulatory actions are taken to decrease theses concentrations. Recent research of Dr. Azim suggests a decline in mercury levels in the Lake Erie, and an increase in the Hg concentration in the fish communities. This research is a follow up study to examine whether the contaminant levels are indeed increasing. In the first chapter we evaluate the temporal trends of polychlorinated biphenyls (PCBs) in Lake Erie fish over the last 30 years by conducting the Exponential and Dynamic Linear Modeling analysis. DLM analysis in the chapter two detects the PCB and Hg contaminant trends in a broader range. There is a high variability in two contaminants trends. These patterns may be because of factors such as fish physiological parameters, and the impact of invasive species. The results of my research will contribute to the Toxics Reduction Strategy.

The Allen Paradox is the observation that, in aquatic communities, there is insufficient prey production to support predator growth. An assessment of the literature reveals that this paradox remains apparent in one of every four studies. Here, a novel explanation for this paradox is proposed: predators that feed in a spatially-heterogeneous-prey environment (SHPE) may experience a greater net energy gain than in a corresponding uniform-prey environment (UPE), meaning that predators may require less food than has been traditionally perceived. A model was developed to simulate a predator’s energy gain while feeding in a SHPE rather than a UPE. According to the simulation, a greater net energy gain in a SHPE than a UPE is possible, but only under certain conditions. Since prey can be utilized more efficiently in a SHPE, a given amount of prey production can supply more predator growth, which can have positive implications in fish stocking.

Along the Toronto shoreline, small coastal embayments (0.4 – 32 ha) are being constructed or modified to restore warmwater fish habitat. I describe how Lake Ontario (hereafter the Lake) alters the thermal regime of these small coastal embayments, how the altered thermal regimes affect growth and survival of age-0 warmwater fishes, and how the thermal habitat quality for such fishes can be improved by altering embayment design. During the warming period of the ice-free season, embayments warm faster than the Lake and so are cooled by exchanges with the Lake. Later in the year Lake exchange warms the rapidly cooling embayments, but the net effect of Lake-embayment exchange is cooling. The degree of cooling in Toronto’s small coastal embayments varies; many have temperatures near that of the Lake, and a few warm as much as local ponds. Age-0 pumpkinseed (Lepomis gibbosus) can fail to reach sufficient size to survive the winter in cooler embayments because their spawning is delayed and their growth is slowed. Most embayments along the Toronto shoreline are too cold to produce age-0 fish that can survive the winter, but all embayments are occupied by age >1 pumpkinseed, suggesting movement from warmer to cooler embayments. Using otolith microchemistry to identify natal embayments of fish, I confirm that age-0 and age-1 pumpkinseed, as well as age-0 largemouth bass (Micropterus salmoides) and age-0 yellow perch (Perca flavescens), exist in metapopulations. Embayment bathymetry is a poor predictor of temperature because almost all embayment flushing rates are very fast, usually 1-2 days. Warmer embayments are located in protected areas of Lake Ontario and receive waters that have already heated substantially. Cold embayments are located along the exposed shoreline of Lake Ontario. To protect embayments from cold lake waters, the cross-sectional area of embayment channels need to be reduced to 1-10% of their current size.

Plant invasions can ensue when plants are introduced to regions without their specialist enemies (the Enemy Release Hypothesis). This assumes natural enemies limit survival and fecundity in an invader's native range. I tested this assumption for a native invasive species, Common Ragweed (Ambrosia artemisiifolia), by excluding natural enemies from seeds, seedlings and adults. At the adult stage, I added disturbance and conspecific density treatments. Protection from herbivores slightly improved performance at the seedling stage only, while disturbance greatly increased survival and fecundity. Increasing conspecific density reduced performance only in disturbed plots. I also tested herbivore tolerance using simulated damage. Heavy (75%) damage did not reduce fecundity; light damage even increased seed production. These results suggest enemies do not limit Ambrosia in its native range, especially compared to the effects of habitat disturbance. While enemy release may have occurred during Ambrosia’s invasions, it is not likely to be their principal cause.

The establishment of exotic species in novel environments is a major environmental concern, however, few long-term studies have examined the effects of these species on their host environment and community, especially in forest ecosystems. The arrival and subsequent spread of the greater European pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Curculionidae, Scolytinae), into southern Ontario pine forests provided a natural experiment to assess biotic interactions between an exotic species and its new community over several years. Reproductive success of Tomicus piniperda colonies of various ages was studied between 2001 and 2004. The size and composition of competitor and natural enemy complexes present in these communities were also quantified over time. The impact of the natural enemy complexes on T. piniperda reproduction was assessed, Brood production (no. eggs and galleries/female) by T. piniperda populations rapidly approached those reported from its native range in Europe, with lower densities of parental adults. Thus, reproduction remained consistently above the replacement level for this beetle over all four years of study suggesting that these recently-introduced populations were growing rapidly and at a greater rate than in their country of origin. Tomicus piniperda successfully integrated into a large bark beetle community, and appeared to be capable of displacing native beetles to more marginal bark habitats, however, these competitors were not eliminated during the course of the study. The long-term effect of this marginalization on populations of native beetles is uncertain. Tomicus piniperda rapidly acquired natural enemies in the introduced areas, however, natural enemy-caused mortality did not show a regulating effect on its populations. It seems that intraspecific competition, rather than predation, regulates T. piniperda populations following introduction. The implications of these findings for the establishment and spread of exotic species in forest systems are examined, especially with reference to a prominent theory for success, the Enemy Release Hypothesis. In short, the Enemy Release Hypothesis is not applicable to an exotic species that is not regulated by natural enemies in its native range, and assessments of the Enemy Release Hypothesis should always include a determination of enemy regulation of the exotic in its native range.

Growth rates are highly variable, both within and among genotypes and populations. The resolution of the trade-off between size and age at maturity has been the study of extensive research by life historians. The fitness advantages of large body size and rapid development time are well supported, leading to two predictions. First, realized growth rates should be maximized. Second, growth rate will be subject to strong stabilizing or directional selection, and consequently, low genetic variability. In real populations, despite the advantages of rapid growth, animals often, in fact, grow at rates lower than the maximum rate that is physiologically possible, even in the absence of external constraints on growth rate (e.g. resource restriction or risk of predation while foraging). This implies that growth may have direct fitness consequences that are independent of the size and age of maturity, thereby lowering the optimal rate of growth. In addition to inducing plastic declines in growth rate, such costs may also select for lower intrinsic rates of growth. Despite the strong fitness effects arising from attaining a large body size quickly, variation in growth rate persists at both the phenotypic and genetic levels. The evolutionary and ecological factors contributing to this variation in growth rate are the focus of this thesis. Growth rate variation in insect model species was produced by the manipulation of resource levels during development. By comparing fitness-associated traits and body composition of adults from different treatment groups, I identify direct costs of rapid growth that could explain why animals benefit from growth at submaximal rates. In the second part of the thesis, the relationship between environmental variation and genetic variance in growth rate is investigated by quantitative genetic analysis of body size at different ages and in different growth environments. The results of this analysis suggest that environmental stress can lead to increased genetic variance via decanalization. This has consequences for the evolvability of growth rates in changing environments.

Sexual conflict and condition-dependent trait expression have emerged as major themes in sexual selection. There is now considerable evidence suggesting that both conflict and condition-dependence can drive the evolution and expression of sexual traits; still, important questions remain concerning the extent to which conflict shapes sexual traits and the role of condition in mediating conflict. Here, I address these two themes in studies of a ladybird mating system. One set of studies investigates the function and economics of potentially antagonistic traits – nuptial gifts and female mating resistance – while another examines condition-dependence in mating resistance and male ejaculate composition. Nuptial gifts are often considered beneficial to females, but recent thinking suggests they may also allow males to manipulate females, raising the possibility of conflict. I demonstrate that male ladybirds benefit from nuptial feeding by their mates through reduced re-mating frequency. Benefits to female reproduction and lifespan, however, are weak or non-existent. These results show that although males gain from transferring gifts that influence female behaviour, females experience neither harm nor benefit. I next tested the hypothesis that nuptial feeding is maintained – despite an absence of benefits – because female foraging is generally elevated after mating. However, although females indeed display strongly increased foraging after mating, this response did not increase nuptial feeding. Recent studies suggest that individual condition may affect the economics of mating and extent of conflict. Female ladybirds vigorously resist mating, and I show that (1) resistance is condition-dependent, with low-condition females displaying more resistance, and (2) resistance functions to minimize superfluous matings (sexual conflict), rather than to select among males (indirectly benefiting females). Resistance generates selection favouring large males; thus, this work demonstrates that ecological circumstances, through influencing condition, affect the strength of sexual selection. Finally, male condition may influence investment in ejaculate components, but condition-dependence in ejaculate composition is currently poorly understood. I show that, in agreement with theory, males in poor condition transfer smaller ejaculates that nonetheless contain more sperm, but less seminal fluid. Taken together, this work highlights both the value of economic studies in evaluating sexual conflict, and the significance of condition-dependence for sexual selection.