Ecology

This study examines the foraging strategies of Mesolithic foragers in the Central Balkans, particularly those employed by the occupants of Crvena Stijena, Montenegro. The Prey Choice Model, Patch Choice Model, and Marginal Value Theorem are used to interpret subsistence patterns. The data from the Crvena Stijena assemblages are compared to those from other Mesolithic sites in the region, along with an Upper Paleolithic assemblage at Crvena Stijena, to assess patterns of animal resource use throughout the Late Pleistocene and Early Holocene in the region. Red deer (Cervus elaphus), roe deer (Capreolus capreolus), wild boar (Sus scrofa), and brown hare (Lepus europaeus) are the most commonly identified taxa in the assemblages. The analysis suggests that Mesolithic foragers at Crvena Stijena, and at many sites throughout the region, were primarily exploiting high-ranked prey types. There is evidence that Mesolithic foragers engaged in more intensive subsistence strategies than those of Upper Paleolithic foragers.

Author Keywords: Central Balkans, Early Holocene, Human Behavioral Ecology, Late Pleistocene, Mesolithic, Zooarchaeology

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

Arctic breeding shorebirds are often considered alternate or secondary prey to avian and terrestrial predators that primarily feed on cyclic populations of rodents. Predation risk can strongly influence habitat selection; however, there is limited understanding of how nest placement by shorebirds and subsequent risk of nest predation are affected by spatiotemporal patterns involving the indirect effects of alternate prey on predator activity. I examined nest fates of Whimbrel (Numenius phaeopus) and Dunlin (Calidris alpina) at the southernmost edge of their breeding ranges at Polar Bear Provincial Park, Ontario, using field surveys including direct observations, camera monitors and thermal probes. I used resource selection functions (RSFs) to compare used and available habitat features near shorebird nests. I assessed whether shorebird nest predation was affected by spatial patterns in avian predator activity, habitat, and small mammal alternate prey and annual variation in cyclic small mammal abundance. RSFs confirmed strong habitat selection for graminoid fen habitats with avoidance of tundra heath, presumably to avoid terrestrial predators that may use them as travel corridors. Shorebird nest predation was not affected by the spatial variation in avian predator activity. However, Dunlin nest predation risk was affected by spatial variation in small mammal abundance. Further, the effect was strongest in years consistent with peaks in the small mammal population cycle. These findings highlight the important effects of spatiotemporal variation of alternate prey densities on Arctic-Subarctic food webs, providing insights on the complex relationships affecting shorebird nest success.

Author Keywords: apparent competetion, Dunlin, Empirical Bayesian Kriging, Shorebird, Subarctic, Whimbrel

Darwinian fitness is determined by the outcome of allocations of energy and nutrients to plant growth, survival, and reproduction. Allocations to reproduction differ from allocations to growth and survival because the products of reproduction (pollen, ovules, and fruits) are dispersed away from the plant and so the resources used to produce them cannot be re-allocated. As a result, and because the total resource pool available to a plant is limited, allocations to reproduction can reduce future growth, reproduction, and/or survival, yielding fitness costs of reproduction. This study provides a novel approach to detecting the costs of reproduction through multiple reproductive currencies, including both biomass and nitrogen allocations and their temporal effects on current and future plant performance. My results demonstrate the environmental dependence of the costs of reproduction and show that under certain conditions, males can bear greater costs than females, contrary to the prevailing view.

Author Keywords: Cost of reproduction, dioecy, flower removal, life-history trade-offs, photosynthetic machinery, sexual dimorphism

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

The Lesser Yellowlegs (Tringa flavipes) is a steeply declining shorebird that breeds across boreal North America. I studied nest survival in Anchorage, Alaska, USA and Churchill, Manitoba, Canada and nest site selection factors in Churchill. Nests were monitored at each site and daily nest survival rates (DSR) were calculated based on a maximum likelihood approach. Overall nest survival was ~63% for Anchorage (lcl–ucl = 0.450–0.773, n=49) and ~28% (lcl–ucl = 0.113–0.481, n=26) for Churchill. Earlier initiation dates, warmer mid-incubation temperatures and lower temperature variability during nesting were linked with higher DSR. I tested nest site selection at territorial and microhabitat scales using multiple logistic regression to compare nest sites with random points. Lesser Yellowlegs selected territories further from water and, at the microhabitat scale, taller shrubs. Projected climate-related shifts in weather and habitat will likely present both benefits and challenges to Lesser Yellowlegs.

Keywords: Lesser Yellowlegs, Tringa flavipes, shorebird, nest survival, nest success, nesting habitat, breeding habitat, boreal, sub-arctic, climate change, Anchorage, Alaska, Churchill, Manitoba

Author Keywords: boreal, breeding habitat, Lesser Yellowlegs, nest survival, shorebird, Tringa flavipes

I used 31 years of Semipalmated Plover (Charadrius semipalmatus) population data to assess the effects of vital rates on a local breeding population of plovers in Churchill, Manitoba, Canada. I used three similar Bayesian Integrated Population Models (IPMs), with the last a coupled IPM population viability analysis (PVA) approach to predict the impact of changing spring temperatures on future population size. I estimated adult and juvenile apparent survival, fecundity, immigration rate, and yearly population size estimates, and I found that population growth rate was most highly correlated with immigration and adult apparent survival. Moreover, I found that the population remained relatively stationary with a slight decline in recent years. I also found a significant positive effect of spring average daily minimum temperature on juvenile apparent survival. I used this effect to inform my PVA and to evaluate the risk of quasi-extinction for 20 years after the end of the study. I found a low quasi-extinction risk and a greater probability of the population increasing in the next twenty years when informed by predicted spring temperatures from global climate models. My findings suggest some resilience of this species to one effect of climate change and emphasize the importance of continued monitoring to assess if declines in this species will change as multiple threats to their existence in the sub-arctic progress.

Author Keywords: Bayesian, Climate change, Integrated population model, Population dynamics, Population viability, Semipalmated Plover