Biological Sciences - Theses, Dissertations, and other Required Graduate Degree Essays

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Habitat use and the impacts of agricultural land use for wintering Neotropical migrants

Author: 
Date created: 
2020-01-10
Abstract: 

For six months of each year, Neotropical forests host the highest known diversity and density of wintering migrants. Habitat loss and conversion of more than 3.5 million ha of Neotropical forests a year is frequently linked to declines in Neotropical migrants, however, data on habitat use in the wintering grounds is very limited. In this thesis, I examine habitat use, across three land cover types for wintering Yellow Warblers (Setophaga petechia) and show that in the lowlands of Jalisco, Mexico, seasonal agriculture with hedgerows, provides high quality winter sites. Yellow Warbler originating from Western Canada, were found in the highest densities in agricultural habitats, intermediate in riparian forests and lowest in coastal scrub-mangrove. Birds wintering in agriculture and riparian forest had higher apparent monthly survival compared to birds in scrub-mangrove and were able to regrow higher quality replacement tail feathers. However, I found no evidence that traits linked to competitive ability (age, sex, or size) influenced the distribution of birds across different land covers. Together, these results demonstrate that current agricultural practices in western Mexico are unlikely to have contributed to the decline of Yellow Warbler populations in Canada. Overwintering in agriculture did not appear to negatively impact the Neotropical migrant community in western Mexico. Neotropical migrants were more abundant in agriculture, and had similar species diversity and beta-diversity to riparian forests. In contrast, although a few resident species were frequently found in agriculture, resident species had lower species diversity in agriculture compared to riparian forest community. Collectively these results demonstrate that individual species, and particularly the Neotropical bird community can utilize human altered landscapes on the wintering grounds in Mexico. However, native habitats are key to retaining the full resident bird community. Identifying the features and spatial configuration of the working land that supports bird populations will be critical for the management and conservation of resident and overwintering birds.

Document type: 
Thesis
File(s): 
Supervisor(s): 
David Green
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) Ph.D.

Efficacy of the European Earwig (Forficula auricularia) as a generalist biocontrol agent

Author: 
Date created: 
2025-12-13
Abstract: 

The European Earwig (Forficula auricularia) has been the subject of scientific curiosity and public disdain since its introduction to North America due to its controversial status as both a natural enemy of agricultural pests, and as a nuisance cohabitant of human dwellings. I aim to investigate the feasibility of utilizing the earwig as a biocontrol agent against target pests of organic apple orchards, as well as its efficacy as a generalist predator in the context of agricultural ecosystems. Through DNA gut-content analysis, and cross-seasonal field observations, I was able to confirm that earwigs are consuming apple orchard pests under natural conditions. These findings are corroborated upon further analysis of field data which show a negative association between earwig abundance and multiple species of pest prevalence at tree-level occupancy across the field season. I examine predation efficacy and consumptive thresholds of the earwig in the context of generalist predator traits through temperature controlled functional response laboratory experiments for two recognized apple pest species, the rosy apple aphid (Dysaphis plantaginea), and the oblique-banded leafroller (Choristoneura rosaceana). Earwig predation was independently affected by density and temperature, but no interaction effect was observed. Analysis of the data did not accurately describe a type II functional response relationship, showing the limitations of traditional predator-models for describing predation behaviour of generalists in biocontrol practice. The preponderance of evidence outlined in this thesis provides promising evidence for utilizing European earwigs in conservation biocontrol, elucidates their role as key predators in agroecosystems, as well as reconsiders how to approach the study of generalist predators in biocontrol research and traditional predator-prey models.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Jenny Cory
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.P.M.

Reproductive trade-offs in the click beetle, Agriotes obscurus, exposed to the fungal pathogen Metarhizium brunneum

Author: 
Date created: 
2019-09-20
Abstract: 

Several of the more pathogenic fungal species that infect insects have been developed as biological control agents. Adult insects can respond to potentially lifespan-reducing pathogen challenges by fighting infection, allocating resources to resistance over other activities. Alternatively, they can allocate resources to maximizing fecundity in response to early death, the terminal investment hypothesis. The click beetle Agriotes obscurus is an agricultural pest, and the fungus Metarhizium brunneum is being developed as a control agent. I examined the impact of M. brunneum challenge on A. obscurus reproduction and whether this changed under different nutritional conditions in beetles of varying ages. Beetles reduced their preoviposition period in response to fungal-induced decreases in lifespan when they were older, resulting in maintained fecundity, or under starved conditions, although fecundity could not reach the level of fed beetles. These results suggest that M. brunneum should be used early in the season when resources are abundant.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Jenny Cory
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.P.M.

Conceptual and applied approaches to marine invasions

Author: 
Date created: 
2019-09-24
Abstract: 

The accelerating rise in global trade and travel means that our world is more interconnected than ever before. This trend could severely impact species and ecosystems globally, as it increases opportunities for species to invade regions beyond their natural range. In this thesis, I combine ecological theory and data synthesis with empirical field-studies to tackle the questions of what makes some communities more easily invaded than others, and how can both natural and anthropogenic control interventions affect the persistence and impacts of invasive species. I first evaluate the relationship between native species diversity and invasibility, or the vulnerability of a community to invasion. Using a meta-analytic approach, I show that the conflicting patterns between diversity and invasibility that are often observed in the literature are likely due to not only differences in spatial scales between studies but also to differences in the metrics researchers use to measure invader success. I then use the invasion of Caribbean coral reefs by the predatory Indo-Pacific lionfish as a model system to test natural and anthropogenic means of controlling the invader. Using a combination of fisheries-derived sampling of native grouper predators and a field experiment conducted across a gradient of grouper abundance, I examine the ability of native grouper predators to mitigate the negative effects of lionfish predation in the Bahamas. I reveal little evidence for direct predation by groupers on lionfish, but show that fear of native groupers alone by lionfish is sufficient to evoke behavioural changes in lionfish that could potentially reduce their impact on native prey. Finally, I use a long-term field experiment to investigate the ecological effectiveness of infrequent culling (i.e., the physical removal of lionfish from reefs by divers). I demonstrate that infrequent culling can reduce lionfish abundance, but is insufficient to halt the decline in native prey fish biomass. Moreover, I show that large-scale natural disturbances, like hurricanes, and density-dependent movement by lionfish from neighbouring reefs can undermine culling efforts. Overall, my thesis reveals that the development of standardized metrics is key to generate a holistic understanding of invasion dynamics, and that both natural and anthropogenic control over invaders is unlikely to stymy biological invasions at the scale currently observed for Indo-Pacific lionfish in the Caribbean.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Isabelle M. Côté
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) Ph.D.

Repurposing historical data to investigate aerial insectivore declines

Date created: 
2019-09-09
Abstract: 

Populations of aerial insectivores have decreased since the mid-1980s, possibly due to declines in their prey. However, long-term data on insect abundance in North America are lacking. I evaluated whether brood size manipulation experiments could be repurposed to assess changes in insect availability. A literature review found no evidence that parents’ ability to respond to a challenge has changed over time, but study methods varied widely. Therefore, I replicated a brood size manipulation experiment conducted on tree swallows in 1994/1995. Parents did not change how they responded to changes in brood size. However, delivery rates were consistently lower in 2017/2018 because parents delivered smaller boluses and tended to visit the nest less. These results are consistent with the hypothesis that aerial insectivores are declining due to reduced insect availability, but could also arise for other reasons. My thesis highlights the value of historical data for investigating aerial insectivore population declines.

Document type: 
Thesis
File(s): 
Supervisor(s): 
David J. Green
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.Sc.

The evolutionary origins of amphibian extinction risk

Author: 
Date created: 
2019-09-18
Abstract: 

The rise of humanity to ecological dominance has precipitated concerted patterns of environmental change across every biome on Earth. Human activities can upend the adaptive landscapes on which species' have evolved, causing the sudden maladaptation of lineages to these novel conditions. Amphibians are amongst the most threatened vertebrates, with contemporary extinctions driven by multiple interacting stressors including habitat destruction, introduced pathogens, and climate change. Despite these looming threats, we understand little about how or why susceptibility to these stressors varies across amphibian lineages. In this thesis, I investigate the evolutionary origins of modern extinction risk in the Amphibia, by examining comparative patterns of susceptibility to various drivers of extinction. First, I show that modern extinction risk positively covaries with speciation rates across amphibian genera due to the most rapidly-diversifying clades producing numerous range-restricted and vulnerable species. Second, I demonstrate how evolutionary dynamics may influence local-scale extinction by examining amphibian species' responses to deforestation across the world. Contrary to patterns of global threat, the slowest-diversifying amphibian lineages are disproportionately lost from human-modified ecosystems - which may reflect a relationship between diversification and niche lability. Third, I examine phylogenetic and trait-based patterns of susceptibility to a human-dispersed fungal pathogen. Though species' ecology and life history consistently shape infection patterns across diverse amphibian assemblages, these traits appear to bear little weight for species' extinction risk from disease epidemics. Fourth, I test the relative effects of both dehydration and temperature on performance, and therefore climate risk, in three ecologically diverse anuran species. Performance was maintained across broad thresholds of dehydration in all species, but warmer temperatures accelerated the onset of performance decline. Species-specific biophysical modelling revealed stark differences in how dehydration is likely to limit activity in each species, suggesting that desiccation physiology may be an important driver of extinction risk from climate change in amphibians. These studies collectively illustrate that amphibian species' responses to anthropogenic environmental change have deep evolutionary roots. In turn, we can expect our continued environmental dominance to fundamentally reshape the evolutionary tree of amphibians into the future.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Wendy Palen
Arne Mooers
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) Ph.D.

The effect of spawning salmon subsidies on reproduction and territoriality of an avian insectivore

Author: 
Date created: 
2019-02-06
Abstract: 

Resource subsidies link marine, freshwater and terrestrial ecosystems. The movement of marine-derived nutrients from spawning salmon into riparian forests through multiple trophic pathways provides an important subsidy to recipient terrestrial ecosystems. Studies have established links between salmon subsidies and higher densities of indirect consumers, such as insectivorous birds. However, the mechanisms supporting these higher densities remain largely unexamined as studies have focused on patterns rather than processes. This thesis examines the mechanisms and trade-offs supporting higher densities of Pacific wrens (Troglodytes pacificus), a species of avian insectivore, along salmon streams. I found that salmon subsidies mediate habitat selection and reduce territory sizes of adult male wrens along riparian forests. I then examine the effect of salmon subsidies on reproductive success and effort. Thus, not only do salmon subsidies shape spatial occurrence of adult wrens, they also impact breeding behaviour and effort, leading to higher wren reproductive success on salmon streams.

Document type: 
Thesis
File(s): 
Supervisor(s): 
John Reynolds
Department: 
Science: Biological Sciences Department
Thesis type: 
(Thesis) M.Sc.

The effects of the anti-sea lice chemotherapeutants Salmosan® and Interox® Paramove® 30 on marine zooplankton

Author: 
Date created: 
2020-01-27
Abstract: 

Sea lice infestations can be harmful to both wild and farmed salmon. The Atlantic salmon aquaculture industry relies on the use of chemotherapeutants to control sea lice outbreaks, which can have both economic and ecological impacts. With treatment, several chemotherapeutants are released directly into the water column, potentially exposing non-target organisms. The lethal and sublethal effects of two anti-sea lice chemotherapeutants, Interox® Paramove® 30 and Salmosan®, were examined in wild zooplankton assemblages, wild brachyuran and porcelain crab zoea, and cultured marine copepods (Acartia tonsa). The lowest LC50 values for Interox® Paramove® 30 and Salmosan® of 4 mg/L (CI 4 – 6.9 mg/L) and 54 µg/L (CI 32 – 90 µg/L), respectively) were found for wild zooplankton exposed for 3-h with a 48-h recovery period. The highest Interox® Paramove® 30 LC50 value was 55 mg/L (CI 30 – 95 mg/L) for brachyuran crab zoea using a 1-h exposure, and the highest LC50 value found for Salmosan® was 529 µg/L (CI 333 – 900 µg/L) using a 1-h exposure for wild zooplankton. In terms of sublethal affects, Acartia tonsa naupliar development was more sensitive to both chemicals compared to hatching and reproductive success. After exposure to Interox® Paramove® 30 or Salmosan®, the 3-h naupliar development EC50 values were 0.12 mg/L (CI 0.08 – 0.18 mg/L) and 30 µg/L (CI 20 – 41 mg/L), respectively. The least sensitive Acartia tonsa endpoint tested was immobility after hatching: eggs exposed for 1-h to Interox® Paramove® 30 had an immobility EC50 value of 7.3 mg/L (CI 3.2 – 72 mg/L). In contrast, Salmosan® had no observable effect after a 1-h exposure of Acartia tonsa eggs up to 7500 µg/L. Collectively, these results provide novel toxicity data for two chemotherapeutants to planktonic organisms which will support the safe and appropriate regulation of these aquaculture chemicals in Canada.

Document type: 
Graduating extended essay / Research project
File(s): 
Supervisor(s): 
Chris Kennedy
Department: 
Science: Biological Sciences Department
Thesis type: 
(Project) M.E.T.

Effect of diluted bitumen on the survival, physiology, and behaviour of the zebra finch (Taeniopygia guttata)

Author: 
Date created: 
2019-11-27
Abstract: 

Given ongoing and potential increases in shipment of diluted bitumen (dilbit) out of the port of Vancouver, there is a need for toxicity data to assess the impact of catastrophic dilbit spillage on wildlife. Peer reviewed literature on dilbit toxicity is limited to teleost fish, despite the importance of coastal waters as habitat for diverse bird fauna. We used the zebra finch (Taeniopygia guttata) as a tractable, avian model system for preliminary studies on Cold Lake blend dilbit. Objectives were to establish methodology appropriate for determining dilbit toxicity to birds, determine a range of lethal and sublethal doses, and obtain physiological and behavioural endpoints. We conducted three 14-day exposure trials with dosages from 0-12 ml dilbit/kg bw day. Mortality was associated with mass loss, external oiling, elevated OXY, and decreased pectoral muscle mass. In addition, evidence for sub-lethal effects included elevated EROD, increased wet gizzard mass, and behavioural changes.

Document type: 
Graduating extended essay / Research project
File(s): 
Supervisor(s): 
Tony D. Williams
Department: 
Science: Biological Sciences Department
Thesis type: 
(Project) M.E.T.