Ecology

Lake whitefish (Coregonus clupeaformis) are ecologically, economically, and culturally significant across their range, yet little is documented about the species' spawning behaviour. Recruitment of lake whitefish has dramatically declined over the past two decades across many regions of the Laurentian Great Lakes, most notably in lakes Huron and Michigan, prompting research efforts to fill critical knowledge gaps in the life history of this species. Understanding the reproductive ecology of lake whitefish, including documenting aspects of spawning behaviour, may reveal clues about factors contributing to the declines. This study used fine-scale acoustic telemetry to characterize sex-specific movement patterns and habitat associations of lake whitefish during the spawning season. A VEMCO Positioning System (VPS) was deployed at an active spawning shoal in Georgian Bay (Lake Huron), with guidance provided by Saugeen Ojibway Nation members with local ecological knowledge about the shoal and the lake whitefish population. In the fall of 2020, 50 lake whitefish were captured and tagged at the spawning shoal; 28 of those fish were observed the following spawning season in 2021. A clear increase and decrease was observed in the presence of individuals in the study area over the spawning period. Both sexes moved into shallower waters at night and deeper waters during the day at rates of 0.162 m/h and 0.08 m/h, respectively. Decreased rates of movement and horizontal distance travelled were detected during the day leading up to a peak activity phase where 22 fish were present. At night during this peak activity phase, males moved 30.0% faster on average than females (0.204 ± 0.13 and 0.143 ± 0.10 m/s, respectively). This study provided a unique opportunity to work with local First Nations to understand lake whitefish spawning behaviour, providing insights into the reproductive ecology of a population undergoing concerning declines in recruitment and abundance.

Author Keywords: Coregonine restoration, Coregonus clupeaformis, Fine-scale acoustic telemetry, GLATOS, Spawning habitat, Two-Eyed Seeing

The Great Lakes represent nearly a fifth of the global freshwater surface supply, and support culturally, economically, and ecologically important fish species such as Walleye (Sander vitreus). With water temperatures projected to rise by several degrees in the coming century, understanding the energetic impacts on fishes is crucial for effective habitat and fisheries management. I measured the swimming performance, accelerometer-based activity, and metabolism of walleye in relation to body size, sex, and water temperature to assess potential responses to climate variability. Both acceleration and swim speed predicted metabolic rate with reasonable accuracy. Temperature had a positive effect on oxygen consumption whereas body mass had a negative effect. Critical swimming speed increased with temperature, and tailbeat frequency had positive relationships with swim speed and acceleration. My laboratory-based calibrations should enable remote field monitoring of energy use of walleye (via accelerometers) and help conserve an important species through bioenergetic modelling.

Author Keywords: accelerometry, bioenergetics, climate change, metabolism, respirometry, walleye

Acoustic communication is vital for mediating interactions between individuals and their environment. From echolocating bats to isolated rodent pups, ultrasonic vocalizations are a useful mechanism for producing localized and cryptic acoustic signals. Flying squirrels have been demonstrated to produce almost exclusively ultrasonic calls which is rare in both squirrels and mammals, though the significance of this acoustic range is unknown. To investigate the context of ultrasonic calls in these gliding mammals, I created phylogenetic comparative analyses to compare ecological and morphological traits against call frequencies. I found that nocturnality, a trait entangled with gliding in squirrels, was related to higher-frequency calls. Furthermore, by comparing all gliding mammals and their non-gliding counterparts, I found that gliding mammals produce significantly higher frequencies than these relatives. This form of cryptic communication is likely used to avoid predation, which was further supported by behavioural experiments wherein flying squirrels used significantly higher frequencies when predation risk increased. While high frequency communication was used by most gliders, I found that ultraviolet-induced photoluminescence, another potential form of crypsis, was strongly associated with nocturnality, with half of the tested gliding mammals showing evidence of this unique colouration. While ultrasonic vocalizations are widespread in echolocating bats and echonavigating mammals, I did not find evidence to support echonavigation in flying squirrels. Instead, I found that ultrasonic vocalizations are used in a variety of social contexts and during solitary foraging and exploration. These combined results demonstrate the unique ecological and evolutionary pressures acting on small-bodied, nocturnal gliding taxa and the resulting cryptic behaviours and communication.

Author Keywords: communication, flying squirrels, gliding mammals, Sciuridae, ultrasound, ultraviolet-induced photoluminescence

I tracked summer movements and activity of snowshoe hares (Lepus americanus) in southwestern Yukon, Canada, during their population cycle (2015–2022) to assess the primary drivers of movement. Hares exhibited variable movement and activity during the cycle, exhibiting increased home range size and higher daily displacement during low population densities. Males exhibited more dramatic increases in their home ranges (>3-fold), and had greater and more variable movement rates and time spent travelling than females. The ratio of predators to hares was highest at low hare densities when hares were moving most, and seasonal activity of hares seemed unrelated to that of predators. Differences between sexes imply that reproductive activities likely were the main driver of hare movement variation rather than food availability. These findings reinforce that, even in highly variable environments, potential rewards associated with successful mate search and reproduction may outweigh the risks associated with reproductive behaviour.

Author Keywords: behaviour, boreal forest, GPS telemetry, home range, movement ecology, predation risk

Muskrat populations are declining across North America. In recent decades, hybrid cattail Typha x glauca has been invading wetlands in North America. This invasion is degrading wetland habitat, leading to reduced interspersion of water and vegetation. Muskrats are wetland-obligates and their populations are positively linked to marsh interspersion. Therefore, muskrat populations may be declining due to the invasion of T. x glauca and subsequent reduction in interspersion. To test this hypothesis, I first sampled marshes across south-central Ontario, comparing muskrat densities with the relative frequency of T. x glauca and the degree of interspersion. Second, I measured intensity of use by muskrats in a large wetland along a gradient of interspersion. My findings suggest that reduced interspersion may be contributing to muskrat population declines, but it is unclear to what degree T. x glauca is responsible. Further research is needed to understand the effects of wetland invasions on muskrat populations.

Author Keywords: invasive species, Ondatra zibethicus, Southern Ontario, Typha x glauca, wetlands, wildlife conservation

I investigated the climate vulnerability of a cold-water salmonid by observing the upper thermal tolerance of brook trout (Salvelinus fontinalis) across multiple life stages. Using hatchery- and wild-ancestry fish, I assessed variation in thermal tolerances and carryover effects within and among brook trout life stages and populations that were reared under varying winter thermal regimes as embryos. Embryonic, fry, and gravid adult upper thermal tolerance were tested via CTmax. Warm acclimation was associated with an increase in embryonic upper thermal tolerance. CTmax variability was markedly higher in embryos than juvenile or adult salmonids. Effects of thermal incubation treatments varied by life stage, with incubation temperature and life stage both influencing body size and thermal tolerance. Collectively, these results suggest that brook trout only exhibit short-term carryover effects from thermal stressors during embryo incubation, with no lasting effects on phenotype beyond the first few months (10 weeks) after hatch.

Author Keywords: acclimation response, climate change, ontogeny, salmonid, stress, thermal plasticity

Animals are essential to freshwater biogeochemistry and productivity. Through their excretion, aquatic consumers release bioavailable nutrients and carbon that can vary with animal taxonomic rank, trophic position, and abiotic factors such as light and nutrient supply. In fresh waters, light and nutrient supply is often modulated by dissolved organic matter (DOM), a "murky" component in the water that gives it a brown color and that may indirectly affect animal nutrient and carbon excretion. Additionally, contaminants can impact animal physiology, altering metabolism and inducing stress, further affecting nutrient and contaminant excretion. The size and structure of the ecosystem, including community composition and biomass, can also impact the contribution of aquatic animals to the elemental pool. To understand these dynamics, I examined animal‐mediated elemental cycling in freshwater ecosystems across gradients of DOM concentration and composition and under contaminant exposure. I tested fish and invertebrate nitrogen, phosphorus, and DOM excretion across trophic positions during two sampling events in Lake Erie and in naturally DOM-variable streams and lakes. I also investigated the effects of chronic exposure to silver nanoparticles (AgNP) under environmentally relevant conditions on fish nutrient and silver (Ag) release. I found that aquatic animals can be a substantial nutrient contributor to the nutrient pool, particularly when their population biomass is high and ambient nutrient concentrations are low. I also detected nonlinear relationships between animal nutrient excretion and DOM characteristics that varied with taxonomic rank and trophic position and that dampened at larger ecological scales. Importantly, I identified several fish DOM excretion signatures that differed relative to ambient DOM and reported the first fish Ag excretion rates under AgNPs exposure. My results underscore the context-dependency and variability inherent in animal-mediated elemental cycling, highlighting the critical role of animals as both modifiers and conduits of nutrients, DOM, and contaminants in aquatic ecosystems.

Author Keywords: carbon, consumer-nutrient driven dynamics, ecological stoichiometry, nitrogen, phosphorus, silver nanoparticles

We studied the physiological and molecular responses of lab-grown Daphnia pulex to shifts in dietary (carbon, nitrogen, phosphorus, and cyanobacteria) and growth media (calcium) nutrient supply using a set of potential biomarkers via qPCR. Each examined nutrient had a strong effect on Daphnia mass-specific growth rate, and we found significant dose-dependent effects of treatment level (medium and low) on the gene expression of selected indicator genes. Furthermore, linear discriminant analysis models using different combinations of treatment levels could separate the animals between nutritional treatments with 86-100% prediction accuracy. This would suggest that Daphnia appear able to respond to nutrient limitation by adjusting their growth rate and associated molecular pathways to deal with an insufficient supply of nutrients. While this study provides valuable information regarding Daphnia's ability to adjust physiological and molecular processes under controlled laboratory conditions, more validation needs to be conducted before applying these potential biomarkers to wild populations to assess the type and intensity of nutritional stress.

Population cycles are characterized by predictable temporal oscillations in population size and are influenced by densities of both predators and prey. These oscillations are influenced by the predator functional response, i.e. the influence of prey density on predator kill rate. The Canada lynx (Lynx canadensis) is a predatory mammal with cyclic northern populations driven by snowshoe hare (Lepus americanus) density. Despite some understanding of the drivers of lynx cycles, we lack understanding of how lynx hunting behaviour, including kill site selection, is influenced by the spatio-temporal distribution of prey. These concepts are explored in chapter one of this thesis.

In chapter two, we (coauthors and I) built on work in Kluane region of the Yukon where lynx and hare populations have been tracked through several population cycles. Over six winters, we deployed GPS collars on >40 individual lynx, some of which were fitted with satellite transmitters, accelerometers, and audio recorders. We validated the use of these technologies for identifying hare kills with an accuracy of >87%. This validation is the foundation for chapter three of this dissertation.

In chapter three, we investigated the drivers of spatial variation in lynx kills. Using snow track transects through four winters of declining hare density, we developed a robust model of habitat-specific hare abundance over time. Using model predictions, in combination with lynx Utilization Distributions derived from GPS locations and related habitat associations, we determined the importance of hare abundance, lynx spatial use, and landscape characteristics such as vegetation density in determining patterns of lynx kills and space use. Lynx kill sites were most strongly predicted by lynx space use, followed by the relative abundance of hares, an index of tree cover density, and elevation. Lynx space use itself was not strongly predicted by hare relative abundance, but rather by a shift to the use of more open habitats when hares were abundant to higher use of denser habitats as hare populations declined; this apparently corresponded to temporal changes in hare distribution. This thesis helps to disentangle the drivers of spatio-temporal variation in predator foraging behaviour, with important implications for understanding predator-prey dynamics.

Author Keywords: animal behaviour, biologging, foraging, habitat selection, Lynx canadensis, predator-prey dynamics

Quantifying the impacts of environmental conditions on the abundance of wildlife populations is important for making informed management decisions in the face of increasing environmental threats. Managers require robust tools to estimate abundance and density of wildlife rapidly and with precision. Within the context of studying white-tailed deer, I evaluated the use of camera-traps and a recently developed spatial-mark resight model to estimate deer density and evaluate habitat and land use factors influencing deer density. The study was conducted in central Ontario, Canada on approximately 16 km2 of public land including the protected Peterborough Crown Game Preserve. Telemetry locations from 39 radio-collared deer were used and one hundred camera-traps were deployed for a total of 140 days from January 2022 to May 2022. Using telemetry locations and camera-trap photos I built a two-step spatial-mark resight model to estimate deer density. Deer density varied during the study as a portion of the population migrated to wintering areas outside of the study area. Despite fluctuations in precision, estimates improved towards the end of the study as more data became available and deer space use stabilized. The average deer density during the entire study was 3.0 deer/km2 (95% CI= 0.1, 5.8; SD= 1.7; CV= 55%; N= 238 deer). The lowest mean density was 0.2 deer/km2 (95% CI= 0.1, 0.4; SD= 0.1; CV= 50%; N= 15 deer) from February 26th to March 11th and the highest mean density was 4.8 deer/km2 (95% CI= 3.1, 6.2; SD= 0.8; CV= 17%; N= 378 deer) from May 7th to May 20th. When I incorporated spatial covariates into the model to estimate effects on deer density, higher proportions of mixed forest, deciduous forest, and road and trail density all had negative effects on deer density. While models contained some uncertainty, deer density appeared higher in the portion of the study area protected from licensed hunting. This thesis provides a framework for managers to use camera-traps and the spatial-mark resight model to monitor deer populations and link environmental covariates to spatial variation in density. As environmental threats such as habitat loss and infectious diseases increase in severity, monitoring wildlife population numbers will be vital for informed responses to these threats. The two-step spatial-mark resight model with environmental covariates provides managers with a long-term monitoring tool to evaluate management efforts and population health in forested areas.

Author Keywords: camera-trap, chronic wasting disease, landscape ecology, spatial-capture recapture, white-tailed deer, wildlife management