Graduate Theses & Dissertations

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How Abiotic and Biotic Factors Can Alter the Competitive Landscape in an Aggressive Species Complex (Genus
Competition is known to impact population dynamics through both indirect and direct interactions, and direct interactions can often lead to injury in one or both parties. As such, response to injury through tissue regeneration can be important for surviving post-competitive interaction. However, the impacts of outside factors like temperature and genome size (e.g. polyploidy) are not well studied, especially in syntopic systems. We addressed this knowledge gap by comparing regeneration rates of diploid Ambystoma laterale and triploid unisexual Ambystoma at two ecologically-relevant temperatures. Environmental factors appeared to have stronger effects on regeneration than ploidy level, but overall mass was impacted more strongly by ploidy level. Interestingly, there was an interaction between temperature and time within unisexuals that was absent when comparing different ploidy levels, implying temperature has a more complex effect on polyploids. This study supports the hypothesis that polyploid organisms are better equipped to respond to shifts in their environments, which can give them a competitive advantage at the northern range limit of this species complex. Author Keywords: Ambystoma, Genome dosage, Hybrid vigor, Polyploidy, Thermal optimum, Tissue regeneration
Temporo-spatial patterns of occupation and density by an invasive fish in streams
Since its introduction to North America in the 1990s, the Round Goby has spread throughout the Great Lakes, inland through rivers and is now moving into small tributary streams, a new environment for this species in both its native and invaded ranges. I explored density and temporal occupation of Round Gobies in four small streams in two systems in south-central Ontario, Canada in order to determine what habitat variables are the best predictors of goby density. Two streams are tributaries of Lake Ontario and two are tributaries of the Otonabee River, and all of these streams have barriers preventing upstream migration. I found that occupation and density differed between the systems. In the Otonabee River system, Round Gobies occupy the streams year round and the most important factor determining adult density is distance from a barrier to upstream movement, with the entire stream occupied but density highest next to the barriers. In the Lake Ontario system, density is highest at mid-stream and Round Gobies appear to occupy these streams mainly from spring to fall. Adult density in Lake Ontario tributaries is highest in sites with a high percentage of cobble/boulder and low percentage of gravel substrate, while substrate is less important in Otonabee River tributaries. Occupation and density patterns may differ due to contrasting environmental conditions in the source environments and distance to the first barrier preventing upstream movement. This study shows diversity in invasion strategies, and provides insight into the occurrence and movement patterns of this species in small, tributary streams. Author Keywords: biological invasion, Generalised Additive Mixed Model, habitat, Neogobius melanostomus, Round Goby, stream
Contemporary adaptive shifts in the physiology and life history of Pumpkinseed (Lepomis gibbosus) introduced into a warm climate
Contemporary evolution has the potential to help limit the biological impact of rapidly changing climates, however it remains unclear whether wild populations can respond quickly enough for such adaptations to be effective. In this thesis, I used the introduction of native North American Pumpkinseed (Lepomis gibbosus) into the milder climate of Europe over 140 years ago, as a 'natural' experiment to test for contemporary evolution to a change in climate in wild populations. In 2008, four outdoor pond colonies were established in central Ontario using adult Pumpkinseed from two native Canadian populations, and two non-native populations from northeastern Spain. By raising native and non-native Pumpkinseed within a common environment, this design minimized the impact of phenotypic plasticity on differential trait expression, and allowed me to interpret differences in the phenotype among pond-reared Pumpkinseed as evidence of genetic differences among populations. I demonstrated that Canadian and Spanish Pumpkinseed have similar thermal physiology except when acclimated to seasonally warm temperatures; trait differences are consistent with Spanish Pumpkinseed being better adapted to a warmer climate. Populations also had similar overwintering ecology, however some differences, such as higher survival under starvation conditions and greater energetic benefits associated with winter feeding, indicated that Canadian populations are better adapted to harsh winter conditions typical of the native range. Finally, I determined that the relatively fast life history expressed in wild European Pumpkinseed is largely driven by plastic responses to the local environment; however, the higher reproductive investment by European populations has a genetic basis. Most climate change research considers taxa that are expected to be negatively impacted by warming: my research demonstrates that even warm-tolerant taxa that are unlikely to experience strong climatic selective forces can respond to a warming environment through evolutionary changes. The potential for adaptive contemporary evolution in warm-tolerant taxa should be taken into account when predicting future ecosystem effects of climate change, and when planning management strategies for species introduced into novel climates. Author Keywords: climate change, contemporary evolution, fish, non-native species, thermal biology, winter ecology
Syrphidae (Diptera) of northern Ontario and Akimiski Island, Nunavut
Syrphids, also known as hover flies (Diptera: Syrphidae) are a diverse and widespread family of flies. Here, I report on their distributions from a previously understudied region, the far north of Ontario, as well as Akimiski Island, Nunavut. I used samples collected through a variety of projects to update known range and provincial records for over a hundred species, bringing into clearer focus the distribution of syrphids throughout this region. I also analysed a previously un-tested trap type for collecting syrphids (Nzi trap), and report on results of DNA analysis for a handful of individuals, which yielded a potential new species. Author Keywords: Diptera, Ontario, range extension, Syrphidae
Fish and invertebrate use of invasive Phragmites in a Great Lakes freshwater delta
Invasive Phragmites australis ssp. australis (herein “Phragmites”) has established and rapidly spread throughout many coastal areas of the Great Lakes. Known to displace native vegetation communities as it forms large, monotypic stands, Phragmites has a bad reputation when it comes to losses of biodiversity and habitat provision for wildlife. However, the extent to which Phragmites provides habitat for fish and invertebrates in coastal freshwater wetlands remains relatively unquantified. Thus, this study assessed whether fish assemblages and invertebrate communities in stands of Phragmites differ from those in stands of two native emergent vegetation communities, Typha spp. and Schoenoplectus spp. The findings showed significant differences in habitat variables among the vegetation communities in terms of water depth, macrophyte species richness, stem density and water quality. While abundance of the functional feeding group filterer-collectors was found to be significantly less in stands of Phragmites when compared to Schoenoplectus, no difference was observed in invertebrate taxa richness among vegetation communities. Lastly, no difference in fish assemblage or invertebrate community was detected when using multivariate analyses, implying that invasive Phragmites provides habitat that appears to be as valuable for fish and invertebrates as other emergent vegetation types in the St. Clair River Delta. The findings of this study will ultimately benefit the literature on invasive Phragmites and its role as fish habitat in freshwater wetlands, and aid management agencies in decisions regarding control of the invasive species. Author Keywords: aquatic invasive species, aquatic macroinvertebrates, freshwater fish, freshwater wetlands, nMDS, Phragmites
Seasonal habitat use and movement of native brook trout (Salvelinus fontinalis) in urban headwater streams
Coldwater streams are becoming increasingly impacted due to urbanization. Using environmental surveys, mark-recapture and telemetry, I assessed factors influencing seasonal brook trout (Salvelinus fontinalis) habitat use and movement in urban headwater streams in central Ontario between 2017-18. Generalized additive models were used to assess which habitat variables best explained seasonal yearling and older brook trout abundance, while generalized least squares models were used to assess overall trends in radio-tagged brook trout movement. My research demonstrated dynamic patterns in habitat use and movement by urban stream-dwelling brook trout. Yearlings were primarily influenced by water quality (stream temperature, conductivity), while older brook trout were most strongly influenced by stream morphology (depth, undercut bank). Movement occurred disproportionately around the spawning season and was more limited in the smaller, more altered stream. These findings may be used to inform fisheries managers on crucial timing and location of brook trout habitat refugia within urbanized environments. Author Keywords: Brook trout, coldwater stream, groundwater, habitat use, radiotelemetry, urbanization
Detectability and its role in understanding upland sandpiper (Bartramia longicauda) occurence in the fragmented landscape of southern Ontario
Upland Sandpipers (Bartramia longicauda), like many grassland birds, are undergoing population decline in parts of their range. Habitat fragmentation and change have been hypothesized as potential causes of decline. I used citizen-science occurrence data from Wildlife Preservation Canada’s Adopt-A-Shrike Loggerhead Shrike (Lanius ludovicianus) program in conjunction with validation surveys, using similar point-count methods, to examine detectability and determine if landscape level habitat features could predict occupancy of Upland Sandpipers in Southern Ontario. In a single season detectability study, I used Wildlife Preservation Canada’s survey protocol to determine detectability in sites that were known to be occupied. Detectability was low, with six surveys necessary to ensure detection using a duration of at least 18 minutes early in the breeding season. The proportion of open habitat did not affect detection on the landscape. Using a larger spatial and temporal scale, with five years of citizen-science data, I showed that Annual Crop Inventory data could not effectively predict Upland Sandpiper occupancy. Model uncertainty could be attributed to survey protocol and life history traits of the Upland Sandpiper, suggesting that appropriate survey methods be derived a priori for maximizing the potential of citizen-science data for robust analyses. Author Keywords: Bartramia longicauda, citizen-science, detection, landscape, occupancy, Ontario
Effects of Local, Landscape, and Temporal Variables on Bobolink Nest Survival in Southern Ontario
Populations of grassland birds, including the Bobolink (Dolichonyx oryzivorus), are experiencing steep declines due to losses of breeding habitat, land use changes, and agricultural practices. Understanding the variables affecting reproductive success can aid conservation of grassland species. I investigated 1) whether artificial nest experiments accurately estimate the impacts of cattle on the daily survival rate of Bobolink nests and 2) which local, landscape, and temporal variables affect daily survival rate of Bobolink nests in Southern Ontario. I replicated an artificial nest experiment performed in 2012 and 2015 to compare the daily survival rate of artificial and natural nests at multiple stocking rates (number of cattle × days × ha-1). I also monitored Bobolink nests and modeled daily survival rate using local variables (e.g., stocking rate, field use, patch area), landscape variables (e.g., percent forest within 2, 5, and 10 km), and temporal variables (e.g., year, date of season). Results indicate that artificial nest experiments using clay shooting targets overestimated the impacts of stocking rate on the daily survival rate of Bobolink nests. With natural nests, region (confounded by year and field use), stocking rate, and date of season were the strongest predictors of daily survival rate; with stocking rate and date of season both having a negative effect. Management should focus on conserving pastures with low stocking rates (< 40 cattle × days × ha-1), late-cut hayfields, fallow fields, and other grasslands to protect breeding grounds for the Bobolink and other declining grassland bird species. Author Keywords: Bobolink, Daily survival rate, landscape variables, local variables, Nest survival, temporal variables
Discriminating grey wolf (Canis lupus) predation events in a multi-prey system in central Saskatchewan
I investigated if spatio-temporal behaviour of grey wolves (Canis lupus) determined via GPS collar locations could be used to discriminate predation events generally, and among prey species, in Prince Albert National Park during winter, 2013-2017. I used characteristics of spatio-temporal GPS clusters to develop a predictive mixed-effect logistic regression model of which spatial clusters of locations were wolf kill sites. The model suffered a 60 % omission error when tested with reserved data due to the prevalence of deer kills with correspondingly low handling time. Next, I found a multivariate difference in the percentage of habitat classes used by wolves in the 2 hours preceding predation events of different prey species, suggesting that wolf habitat use reflects prey selection at a fine-scale. My results highlight the difficulty and future potential for remoting discriminating wolf predation events via GPS collar locations in multi-prey ecosystems. Author Keywords: Canis lupus, GPS clusters, GPS collars, grey wolf, habitat use, predation
Shorebird Habitat Use and Foraging Ecology on Bulls Island, South Carolina During the Non-Breeding Season
Recent declines in North American shorebird populations could be linked to habitat loss on the non-breeding grounds. Sea-level rise and increased frequency of coastal storms are causing significant erosion of barrier islands, thereby threatening shorebirds who rely on shoreline habitats for foraging. I conducted shorebird surveys on Bulls Island, South Carolina in the winters of 2018 and 2019 and examined habitat selection and foraging behaviour in Dunlin (Calidris alpina), Sanderling (Calidris alba), Semipalmated Plovers (Charadrius semipalmatus), and Piping Plovers (Charadrius melodus). Area, tidal stage, and invertebrate prey availability were important determinants of shorebird abundance, behaviour, and distribution. My study highlights the importance of Bulls Island’s habitat heterogeneity to supporting a diverse community of non-breeding shorebirds. Considering both the high rate of erosion and the increased frequency of disturbance along the shoreline of the island, intertidal habitats should be monitored to predict negative effects of changes in habitat composition and area on non-breeding shorebirds. Author Keywords: foraging behaviour, habitat loss, habitat selection, invertebrate prey, non-breeding, shorebirds
Cytokinins in nematodes
To investigate cytokinins (CKs) in nematodes, CK profiles of a free-living Caenorhabditis elegans and a plant parasitic Heterodera glycines (soybean cyst nematode, SCN) were determined at the egg and larval stages. SCN had higher total CK level than C. elegans; however, CKs in SCN were mostly inactive precursors, whereas C. elegans had more bioactive forms. This is the first study to show that methylthiols are present in nematodes and may affect plant infection. In infectious SCN larvae, methylthiol levels were much higher than in eggs or C. elegans larvae. Furthermore, The CK profiles of SCN-susceptible and resistant Glycine max cultivars at three developmental stages revealed that, regardless of the resistance level, SCN infection caused an increase in root CKs. One resistant cultivar, Pion 93Y05, showed significantly high levels of bioactive N6-isopentenyladenine (iP) in the non-infected roots which indicated a potential role of CKs in soybean resistance to SCN. Author Keywords: Cytokinins, HPLC-MS/MS, Nematode, SCN resistance, Soybean
Shorebird Stopover Ecology and Environmental Change at James Bay, Ontario, Canada
I examined how shorebirds respond to environmental change at a key subarctic migratory bird stopover site, the southwestern coast of James Bay, Ontario, Canada. First, I investigated if the morphology of sandpipers using James Bay during southbound migration has changed compared to 40 years prior. I found shorter, more convex and maneuverable wings for sandpipers in the present-day compared to the historical monitoring period, which supports the hypothesis that wing length change is driven by increases in predation risk. Secondly, I assessed the relationship between migration distance, body condition, and shorebird stopover and migratory decisions. Species that travelled farther distances from James Bay to wintering areas migrated with more characteristics of a time-minimizing migration strategy whereas species that travelled shorter distances migrated with energy minimizing strategies. Body condition impacted length of stay, wind selectivity at departure, groundspeeds, and probability of stopover and detection in North America after departing James Bay. Thirdly, I examined annual variation in dry/wet conditions at James Bay and found that shorebirds had lower body mass in years with moderate drought. In the present-day, drought resulted in lower invertebrate abundance and refuelling rates of shorebirds during stopover, which led to shorter stopover duration for juveniles and a higher probability of stopover outside of James Bay for all groups except white-rumped sandpiper. Finally, I estimated the relative importance of intertidal salt marsh and flat habitats to the diets of small shorebirds and found that semipalmated and white-rumped sandpiper (Calidris pusilla and C. fuscicollis) and semipalmated plover (Charadrius semipalmatus) diets consist of ~ 40 – 75% prey from intertidal marsh habitats, the highest documented in the Western Hemisphere for each species. My research shows that James Bay is of high importance to white-rumped sandpipers, which are unlikely to stop in North America after departing James Bay en route to southern South America. Additionally, intertidal salt marsh habitats (and Diptera larvae) appear particularly important for small shorebirds in the region. My thesis shows that changing environmental conditions, such as droughts, can affect shorebird refuelling and stopover strategies. Author Keywords: body condition, diet, environmental change, migration, ornithology, stopover ecology

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Graduate student theses produced at Trent University. You may also browse theses and dissertations by year, program, or author.

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