December 7, 2018
Lakes in the Great Lakes Basin are vulnerable to regime shifts from oligotrophic to eutrophic states due to climate change and anthropogenic influence. To explore the potential of regime shifts, we examined peak algal biomass using a time series of chlorophyll-a. A continuous time series of chlorophyll-a based on relation of Landsat optical reflectance to in-situ chlorophyll-a was developed for 12,000 lakes for 28 years. Five classes of lake stability were identified: stable oligotrophic; stable eutrophic, eutrophying, unstable, and oligotrophying. We found that eutrophying lakes were shifting from oligotrophic to lakes with a higher trophic status (eutrophication), while oligotrophying lakes were shifting from eutrophic to the lakes with lower trophic status (oligotrophication). We also found that there were more lakes experiencing oligotrophication (3199 lakes) compared to those experiencing eutrophication (2142 lakes). This indicates that despite the fact that both eutrophication and oligotrophication occur simultaneously in the region, eutrophication is still not as ubiquitous as we might think.
Wildlife conservation is one of the most important and challenging tasks in the world today. Before taking measures to protect an animal population, wildlife managers first need to know how many individuals there are in the population. A popular method for estimating population size is capture-recapture, which usually requires captured animals to be identified uniquely and correctly. However, misidentification is a common problem in recent capture-recapture studies relying on natural individual marks that can be identified by DNA samples or photographs. In this talk, I will introduce a general class of hierarchical models that can be used to model capture-recapture data with misidentification. I will also describe a new method for fitting these models, which is based on the saddlepoint approximation method.
November 30, 2018
Climate warming increases metabolism and development rates for organisms, while decreasing their body size. This compounds at the community-level, as small-bodied individuals are more abundant. Warming disproportionally affects higher trophic taxa, such as predators. Predators are important for ecosystem function, as they limit prey populations through top-down control, yet, we know little how predator communities change under warming. My research will examine the effect of warming on predator communities using mesostigmatid mites (Arachnida: Parasitiformes). As warming will increase metabolic costs, I predict that communities will be dominated by small-bodied, generalist predators. I will test this prediction using two field-based experiments, studying the impact of warming on community composition and diet. In addition, I will use a laboratory-based experiment to show the impact of warming on generalist and specialist species.
Theory predicts that parents should alter their level of care to reflect the reproductive value of their brood. Cuckoldry reduces the relatedness of a parent to their brood, thereby reducing its value. Kin recognition – the ability to distinguish kin from non-kin – allows parents to assess brood value and adjust their care. The bluegill sunfish (Lepomis macrochirus) mating system is characterized by cuckoldry, and nest-tending males have been shown to be able to assess relatedness of newly-hatched larvae but not of the eggs. In my proposed study, I will investigate the mechanisms and evolutionary consequences of parental care decisions by testing the hypothesis that nest-tending males adaptively adjust their parental care in response to changes in perceived paternity. I will sample plasma and brain tissue to investigate levels of reproductive hormones and receptors, including prolactin and 11-ketotestosterone, to assess their roles in kin recognition and changes in parental care behaviour.
November 23, 2018
Wing shape of birds is thought to be under strong selective pressures that reflect their need to fly efficiently, exploit habitat effectively, and survive as predator or prey. Wing shape plays a vital role in determining overall flight performance. Low aspect ratio wings (short and blunt) increase take-off speed, which could result in increased predator avoidance. High aspect ratio wings (long and pointed) and low wing loading (large wings compared to body) reduce the energetic costs of flight, which could ultimately increase the overall rate of migration. Most migratory songbirds have differential migration patterns; males arrive at breeding areas before females and older birds arrive before younger birds. If this is facilitated by differences in wing shape, I predict sex and age-related differences in wing shape. I tested these predictions using 20 species of Nearctic-Neotropical migratory birds captured in Long Point, Ontario.
Animals that provide parental care to their offspring often face behavioural trade-offs. Hormones have been implicated in mediating these trade-offs, with androgens often promoting aggressive behaviours at the expense of reduced nurturing behaviour. Conversely, prolactin can promote nurturing behaviour but may reduce aggressive behaviours. We tested the effects of these hormones on parental care in bluegill sunfish, a species in which males build nests and provide sole parental care to the offspring. Immediately after spawning, parental males received one of five hormone manipulations: (1) placebo; (2) 11-ketotestosterone (11-KT); (3) flutamide, an androgen receptor antagonist; (4) prolactin; or (5) bromocriptine, a prolactin-release inhibitor. We found that prolactin-treated males exhibited significantly more nurturing behaviours, whereas 11-KT-treated males exhibited more aggressive behaviours relative to the other treatments. We discuss the hormone-mediated trade-offs during parental care in bluegill sunfish.
November 16, 2018
Anthropogenic changes are causing shifts within ecological communities and subsequently food web structure. In terrestrial and aquatic systems, top-down and bottom-up effects in food webs have been known to cause consistent shifts in community structure and community body size. In soil detrital systems where microarthropod communities are key in carbon and nutrient cycling, community level responses to environmental shifts are understudied. Within the soil detrital microarthropod community, Collembola, commonly known as springtails, are a mid-trophic group susceptible to both top-down and bottom-up forces. To evaluate these effects my study exposed soil dwelling Collembola communities to treatments of warming, nutrient addition and predator addition, to induce top-down and bottom-up effects in both field and lab conditions. Community responses to these treatments reflect potential future responses to anthropogenic change and that may affect decomposition dynamics and carbon storage in soils.
Shade-grown coffee plantations provide wintering Neotropical migrants with an alternative to primary growth forest which is disappearing throughout most of their range. However, it remains unclear whether plantations can provide enough structure to maintain viable wintering populations of many species. We studied Swainson’s Thrush (Catharus ustulatus) wintering in two different sites in the Colombian Andes that consisted of a mixture of montane forest and shade-grown coffee plantation. In comparing the two habitats we looked at several factors that are indicative of habitat quality, such as age/sex hierarchies, home range sizes, density, and migration timing. We also used stable isotopes (δ 13C and δ 15N) to better understand dietary differences between habitats. My research aims to determine whether wintering Neotropical migrants benefit from this agroecosystem and find ways to improve shade-grown coffee practices in the future.
November 9, 2018
Harmful algal blooms are on the rise globally, in which there is a demand for improved historical context and monitoring efforts. This research aims to develop tools for accurate surface chlorophyll- a (chl- a) retrieval (a proxy for algae) within inland lakes as a basis for improved scientific understanding of algal blooms. Landsat satellite images (4-5 TM, 7 ETM and 8 OLI) were used to create a ±30 year predictive model (1984 to 2017), for the following ecoregions: polar, boreal forest, temperate forest, temperate steppe, temperate desert, subtropical humid forests, and tropical moist forests. Regression analyses for 82 algorithms were conducted to determine best fit models (linear, exponential, logarithmic, power) for chl-a and interfering signals of true water colour, total suspended solids, and turbidity to top of atmospheric reflectance. These algorithms were used to assess the usefulness of chl-a predictions within both a regional, and global context.
November 2, 2018
Even though they are hyperdiverse, high biomass, and a vital food source for vertebrate species, soil arthropods are not well understood because they are difficult to directly observe. Many soil-dwelling arthropods (e.g. Coleptera, Diptera) only live in soil for part of their life cycles, emerging when they reach maturity. Along with predatory arthropods on the soil surface, these emergent arthropods connect the soil system to the above-ground food web. In peatlands, soil organisms are exposed to high levels of methylmercury, a neurotoxin, which is shown to bioaccumulate and biomagnify in food webs. My study will examine the diversity of soil-dwelling arthropods and assess arthropod methylmercury content across two peatland sites in central Ontario. Identifying which arthropods have high methylmercury content could help us understand cascading effects of mercury on the environment and for the organisms which feed on arthropods, such as birds.
October 26, 2018
Both freezing and drought stress cause cellular dehydration in plants and elicit similar physiological responses. We examined how spring freezing influences the summer drought tolerance of 6 graminoid (Agrostis stolonifera, Arrhenatherum elatius, Bromus inermis, Festuca rubra, Lolium perenne, Poa compressa), 2 forb species (Plantago lanceolata, Securigera varia) and intact plant-soil mesocosms collected from an old field. In terms of total dry biomass, we found that there were indications of cross-acclimation between freezing and drought stress for Agrostis stolonifera, Bromus inermis, Lolium perenne, Poa compressa and Plantago lanceolata. The decline in biomass under drought was lowest for the plants previously exposed to freezing. In our mesocosm experiment, there was no significant interaction between freezing and drought for total aboveground biomass, despite significant main effects. Overall, our results indicate that there is variation in cross-acclimation responses among species and the latter does not necessarily translate to community level effects.
The degree to which animals move on one scale may be closely related to their other movement patterns. If individuals are prone to movement on multiple different scales, behaviours such as exploration and migration distance may show a consistent relationship. I will assess the relationship between exploratory behaviour and migration distance in a population of song sparrows (Melospiza melodia) using a novel environment test to quantify exploration and stable isotope analysis of claw samples to infer latitudinal migration distance. I will also investigate potential genetic and hormonal mechanisms that may drive this relationship. Preliminary results show variation in exploration levels and migration distance within the population and indicate a positive relationship between the two movement behaviours. A relationship between exploration and migration may suggest a movement syndrome involving the two behaviours and would present important insight into the evolution and consequences of these movements.