http://hdl.handle.net/1974/287 2013-06-19T03:06:02Z http://hdl.handle.net/1974/8080 Title: Factors mediating the distribution and impact of the non-native invertebrate predator Bythotrephes longimanus Authors: Jokela, ANNELI MARIE Abstract: Predicting the impacts of non-native species remains one of the greatest challenges to invasion ecologists. Because of their insularity, freshwater systems are particularly vulnerable to invasions, especially from non-native predators. The research in this thesis explores the role of abiotic and biotic factors in mediating the distribution and impact of Bythotrephes longimanus, a predatory cladoceran that has been introduced to freshwater systems in North America. Although the general impacts of this invasion have been documented, little is known about the factors that modulate them. Using a combination of field surveys and experiments, I tested several hypotheses concerning the influence of interactions with native species, as well as the role of heterogeneity in the light environment, in mediating the impact of Bythotrephes. Results demonstrated that biotic resistance by native macroinvertebrate predators does not play a limiting role in the establishment success of Bythotrephes. However, the within-lake distribution of Bythotrephes was influenced by these macroinvertebrates, suggesting that the native predator context matters when trying to understand the impacts of non-native predators. This was demonstrated with a mesocosm experiment in which the impact of Bythotrephes was constrained by the native Chaoborus larvae. In terms of the abiotic environment, in situ feeding experiments demonstrated that refuges from impact could exist for some prey taxa, as the outcome of predation by Bythotrephes was dependent on light availability and some prey taxa were more successful at evading predation under low light conditions. Finally, results show that adaptive behaviour by prey is also an important determinant of impact, as migrating Daphnia can escape predation effects by Bythotrephes. The combination of light-limited predation and a shallow distribution by Bythotrephes selects for prey that occupy relatively deeper positions during the day. As a whole, this research highlights the importance of complex interactions in mediating the impact of Bythotrephes and may help to explain some of the variation that has been documented among invaded lakes. A better understanding of these complex interactions can improve our ability to anticipate impacts as Bythotrephes continues to spread, as well as provide insight on some of the long-term effects following invasion. Description: Thesis (Ph.D, Biology) -- Queen's University, 2013-06-17 09:26:35.221 2013-06-17T04:00:00Z http://hdl.handle.net/1974/8071 Title: Integrating the effects of climate change and caribou herbivory on vegetation community structure in low Arctic tundra Authors: Zamin, Tara Abstract: Arctic tundra vegetation communities are rapidly responding to climate warming with increases in aboveground biomass, particularly in deciduous shrubs. This increased shrub density has the potential to dramatically alter the functioning of tundra ecosystems through its effects on permafrost degradation and nutrient cycling, and to cause positive feedbacks to global climate change through its impacts on carbon balance and albedo. Experimental evidence indicates that tundra plant growth is most strongly limited by soil nutrient availability, which is projected to increase with warming. Therefore research to date into the mechanisms driving tundra 'shrub expansion' has taken a 'bottom-up' perspective, overlooking the potential role of herbivory in mediating plant-soil interactions. In this thesis, I integrate the impacts of climate warming and caribou browsing on tundra vegetation community structure, and specifically investigate if increases in soil fertility with warming might lead to changes in vegetation biomass and chemistry that could fundamentally alter herbivore-nutrient cycling feedbacks, shifting the role of caribou browsing from restricting shrub growth to facilitating it. Using experimental greenhouses, nutrient addition plots, and caribou exclosures at Daring Lake Research Station in the central Canadian low Arctic, I showed that warming increased soil nutrient availability and plant biomass, and that caribou browsing restricted tundra shrub growth under present conditions. Plant and soil nutrient pool responses to warming demonstrated that increased growing season temperatures enhanced tundra plant growth both by increasing soil nutrient availability and by inferred increases in the rate of photosynthesis, however that the former process was comparatively more limiting. Species- and plant part-specific changes in biomass and chemistry with warming and fertilization clearly indicated the rate and magnitude of change in soil fertility substantially alters plant community structure. Nonetheless, since plant nutrient concentrations decreased with warming and plant responses to browsing were independent of soil fertility, I did not find evidence for a shift from caribou decelerating to accelerating nutrient cycling with warming. Altogether this research indicates effective conservation and management of Rangifer populations is critical to understanding how climate change will affect tundra vegetation trajectories and ultimately tundra ecosystem carbon balances. Description: Thesis (Ph.D, Biology) -- Queen's University, 2013-06-07 15:13:21.698 2013-06-07T04:00:00Z http://hdl.handle.net/1974/8064 Title: BIOCHEMICAL RESPONSES OF ARCTIC SOIL COMMUNITIES TO ANTHROPOGENIC STRESS Authors: Kumar, NIRAJ Abstract: We are living in the era of climate change which becomes more complicated whenever some new environmental issue emerges only to get linked with this already existing challenge. Engineered nanoparticle (NP) contamination is of such issue which may become a major environmental problem under some circumstances in the decades to come. NP-based technologies have proven themselves useful and have the potential for greater promise, but they could become more than a nuisance. Unfortunately, very limited information is available on the environmental impacts of NPs in general and soil in particular. In this thesis, I examined the impact of NPs on soil microbial communities and by trying to avoid the presence of existing NPs I used soil from arctic regions. To examine the effect of another anthropogenic change on the same soil, I investigated the impacts of freeze-thaw cycles (FTCs). This thesis demonstrated that Ag-NPs and Cu-NPs cause a shift in microbial communities. The use of culture-dependent and culture-independent assessment techniques for microbial communities inspired the development of a toxicity indicator. This tool assigned the highest toxicity index to Ag-NPs and a low toxicity to SiO2-NPs. Supporting in vitro studies confirmed that Bradyrhizobium canariense was particularly sensitive towards Ag-NPs. Further analysis showed that a mixture of Ag-, Cu-, and SiO2-NPs were toxic. FTCs were also a significant stress; they had a differential impact upon soil communities derived from different arctic sites. My results suggest that the impact of climate change at high latitudes may not be predictable. Finally, I used a FTC regime shown not have an impact on low arctic sites and compared two different concentrations of Ag-NPs and Ag-microparticles and validated the higher toxicity impact of Ag-NPs on both bacterial and fungal communities. Taken together, these findings represent an initial attempt to try to understand the impacts of two stresses attributable to human activities on arctic soils, soils that are crucial to the health of our planet. Description: Thesis (Ph.D, Biology) -- Queen's University, 2013-06-03 22:36:24.182 2013-06-04T04:00:00Z http://hdl.handle.net/1974/8063 Title: MERCURY AND STABLE ISOTOPES IN COMMON TERNS (STERNA HIRUNDO) FROM THE ST. LAWRENCE RIVER: A COMPARISON BETWEEN BREEDING AND WINTER HABITATS Authors: Baird, CHRISTOPHER Abstract: The Common tern (Sterna hirundo) is considered a sentinel wildlife species for monitoring mercury (Hg) and other contaminants within the St. Lawrence River Cornwall/Massena Areas of Concern (AOC). Here, I investigate the relationship between Hg bioaccumulation and diet using stable isotopes of carbon (δ13C) and nitrogen (δ15N) in adult and chick Common terns from three colonies along a 160 km transect of the upper St. Lawrence River. The foraging range of the colony furthest downstream (EMC) includes both the Massena and Cornwall AOC’s while the two upstream colonies (213 and Ice) are more removed from known point sources of Hg. I also sampled winter- and summer-grown breast feathers to compare diet and Hg exposure on the terns’ breeding ground vs. the terns’ wintering grounds. Hg exposure in summer-grown feathers was significantly higher than Hg exposure in winter grown feathers. Stable carbon (δ13C) and nitrogen (δ15N) isotopes revealed a switch from a marine-based diet during the winter months to a freshwater-based diet on the breeding grounds. Among colonies in summer-grown and chick feathers, the only significant difference in total mercury (THg) exposure was found in chick feathers where Hg was significantly lower at 213 than Ice – both of which are upstream from the AOC’s. However, THg was negatively correlated with δ13C in both winter and summer feathers, and the most parsimonious multi-regression model for winter and summer feathers indicated that δ13C explains 24 and 25% of the variation in Hg exposure, respectively. This suggests terns foraging offshore bioaccumulate more Hg than individuals foraging inshore or in freshwater (winter feathers), and that during the breeding period, terns foraging in pelagic habitats bioaccumulate more Hg than terns foraging in littoral habitats (summer feathers). For the upper St. Lawrence River, these results provide strong evidence that foraging habitat is more important than colony location in determining Hg exposure in a top trophic consumer. Description: Thesis (Master, Biology) -- Queen's University, 2013-06-01 19:35:59.665 2013-06-04T04:00:00Z