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Because differences often exist between species in their tolerances to environmental conditions, locations characterized by extreme parameter values (i.e., high temperature, low DO, high turbidity) may provide refuges from predation or competition by altering the outcome of inter-species interactions. This thesis examined the effects and relative importance of water temperature, dissolved oxygen (DO) and turbidity on habitat use by fish species and resulting changes in community composition. The effects of abiotic factors on predator-prey interactions were tested using field surveys, laboratory experiments, field experiments and computer modeling. Field surveys were conducted in Blind Channel, Delta Marsh, Manitoba, and on Lake Winnipeg, Manitoba, to determine if small bodied forage species preferentially used high temperature, low DO or high turbidity habitats and whether predator species avoided these locations. Prey species were more abundant in these extreme locations at both small (Blind Channel) and large (Lake Winnipeg) spatial scales, but predator avoidance was only documented in Blind Channel. The tolerances of fish species to moderate hypoxia (< 3 mg/L DO) was tested in the laboratory to verify that differences did exist among species and that the observed species distributions were not solely the effect of temperature. To quantify the potential for moderately hypoxic locations to provide a refuge from predation for small fish, a field manipulation was conducted in Blind Channel; hypoxic habitats were created without altering water temperature, decoupling the natural covariation between these two factors that occurs in aquatic systems. The abundance of small forage fish was higher in the hypoxic locations compared to controls and while predators still visited the hypoxic habitats, their mean visit duration was reduced from around 300 min to less than 1 min. An individual based computer model was used to test and illustrate current understanding of the relative importance of temperature, DO and turbidity on predator habitat selection decisions and fish community composition. The model showed that DO had a stronger effect on community composition than temperature, and that reduced foraging success from high turbidity was able to overpower the other two factors. Hypoxia affects habitat selection decisions by fish species and can provide refuges from predation and competition, helping maintain higher species diversity. Water temperature appears to have a weaker effect on fish distributions than DO while turbidity primarily affects visual predators, though the strength of turbidity effects depends on the magnitude and duration of individual events.

Because differences often exist between species in their tolerances to environmental conditions, locations characterized by extreme parameter values (i.e., high temperature, low DO, high turbidity) may provide refuges from predation or competition by altering the outcome of inter-species interactions. This thesis examined the effects and relative importance of water temperature, dissolved oxygen (DO) and turbidity on habitat use by fish species and resulting changes in community composition. The effects of abiotic factors on predator-prey interactions were tested using field surveys, laboratory experiments, field experiments and computer modeling. Field surveys were conducted in Blind Channel, Delta Marsh, Manitoba, and on Lake Winnipeg, Manitoba, to determine if small bodied forage species preferentially used high temperature, low DO or high turbidity habitats and whether predator species avoided these locations. Prey species were more abundant in these extreme locations at both small (Blind Channel) and large (Lake Winnipeg) spatial scales, but predator avoidance was only documented in Blind Channel. The tolerances of fish species to moderate hypoxia (< 3 mg/L DO) was tested in the laboratory to verify that differences did exist among species and that the observed species distributions were not solely the effect of temperature. To quantify the potential for moderately hypoxic locations to provide a refuge from predation for small fish, a field manipulation was conducted in Blind Channel; hypoxic habitats were created without altering water temperature, decoupling the natural covariation between these two factors that occurs in aquatic systems. The abundance of small forage fish was higher in the hypoxic locations compared to controls and while predators still visited the hypoxic habitats, their mean visit duration was reduced from around 300 min to less than 1 min. An individual based computer model was used to test and illustrate current understanding of the relative importance of temperature, DO and turbidity on predator habitat selection decisions and fish community composition. The model showed that DO had a stronger effect on community composition than temperature, and that reduced foraging success from high turbidity was able to overpower the other two factors. Hypoxia affects habitat selection decisions by fish species and can provide refuges from predation and competition, helping maintain higher species diversity. Water temperature appears to have a weaker effect on fish distributions than DO while turbidity primarily affects visual predators, though the strength of turbidity effects depends on the magnitude and duration of individual events.

Mountain ecosystems are considered highly sensitive to the impacts of climate change, and are experiencing a magnitude of change that far exceeds global averages, particularly with respect to increases in average temperature and precipitation. As such, scientists are predicting a rapid habitat reduction or even the loss of the coolest climatic alpine zones, thus threatening the continued survival of high elevation specialists. However, many of these ‘doomsday’ predictions are based primarily on models with coarse-resolution changes to atmospheric climate parameters, and do not take into account the potential buffering effects of other environmental gradients known to structure alpine plant communities, related to topography and soils. To assess the accuracy of predictions regarding the state of vulnerability of alpine plant communities to climate change, this thesis examined the relative importance of climate, topography and soils as determinants of regional alpine plant diversity for all species, as well as for forbs, graminoids and woody species separately, in alpine meadows of southwestern British Columbia. Through redundancy analyses and variation partitioning, results show that topography and soils are more important than climate as determinants of regional alpine plant diversity. Within these groups, elevation, slope, soil moisture and mean summer temperature were most significant. Interestingly, precipitation played only a small role, even though the study area spanned a precipitation gradient of over 1200 mm/year. The stronger influence of temperature, especially for woody species beta diversity, supports findings of shrub expansion in arctic-alpine systems. The lower importance of climate as a determinant of regional alpine plant diversity, especially for forbs, the dominant life form in alpine meadow ecosystems, suggests that these productive environments may be more resilient to on-going changes in atmospheric climate conditions than previously believed. / Graduate

The inherent complexity of the natural world has long been a central theme in ecological research, as the patterns and processes that govern ecosystems can operate at multiple spatial and temporal scales. It is clear that to develop general ecological frameworks, we must consider many different factors at different scales, and incorporate ideas from other disciplines. This thesis touches on several of these ideas, first through an analysis of literature, and then with field research examining the role of broad-scale abiotic factors on lotic systems. To determine how integrated aquatic science is currently understood among different researchers, I provide an analysis on communication and exchange of ideas among various subfields in aquatic science. I show that there are clear divisions within the aquatic science literature, suggesting that there is progress to be made on the integration of methods and ideas. Next, I examine the impact of a large-scale geological feature, the Canadian Precambrian Shield, on abiotic conditions in lotic systems, and how these conditions in turn influence the species assemblages of aquatic organisms. This is addressed with both historical survey data, as well as contemporary data, and as a whole, incorporates ideas concerning the relative influence of regional versus local factors, the importance of historical factors on species distributions, and the relationship between the abiotic environment and biological communities. These analyses show that there are distinct fish and macroinvertebrate communities in Shield lotic systems compared to those found in nearby off-Shield sites, indicating that the Shield is an important broad-scale factor influencing local biological communities. This finding, in conjunction with previous knowledge on the influence of historical factors, provides further insight on the structuring of lotic fish and macroinvertebrate communities in Ontario.

To monitor and assess direct anthropogenic impacts on an aquatic system requires knowledge of its natural variation. The goal of this study explored natural variation in the lake fish communities of the northern Bruce Peninsula, which may act as a reference condition for other studies. The results of this study indicated there has been a shift towards more small-bodied, native species present in the fish communities, potentially a result of beaver activity in the area. A second goal was to calculate gear sampling efficiencies to enable the design of efficient monitoring protocols for fish communities in small, shallow lakes. It was concluded that a wide variety of gears are required to assess the fish species composition in a lake. Fine-mesh hoops were the most effective gear; however, saturation was never obtained for boat electrofishing; therefore, additional research is required to determine effectiveness relative to the fine-mesh hoop net.

The inherent complexity of the natural world has long been a central theme in ecological research, as the patterns and processes that govern ecosystems can operate at multiple spatial and temporal scales. It is clear that to develop general ecological frameworks, we must consider many different factors at different scales, and incorporate ideas from other disciplines. This thesis touches on several of these ideas, first through an analysis of literature, and then with field research examining the role of broad-scale abiotic factors on lotic systems. To determine how integrated aquatic science is currently understood among different researchers, I provide an analysis on communication and exchange of ideas among various subfields in aquatic science. I show that there are clear divisions within the aquatic science literature, suggesting that there is progress to be made on the integration of methods and ideas. Next, I examine the impact of a large-scale geological feature, the Canadian Precambrian Shield, on abiotic conditions in lotic systems, and how these conditions in turn influence the species assemblages of aquatic organisms. This is addressed with both historical survey data, as well as contemporary data, and as a whole, incorporates ideas concerning the relative influence of regional versus local factors, the importance of historical factors on species distributions, and the relationship between the abiotic environment and biological communities. These analyses show that there are distinct fish and macroinvertebrate communities in Shield lotic systems compared to those found in nearby off-Shield sites, indicating that the Shield is an important broad-scale factor influencing local biological communities. This finding, in conjunction with previous knowledge on the influence of historical factors, provides further insight on the structuring of lotic fish and macroinvertebrate communities in Ontario.

To monitor and assess direct anthropogenic impacts on an aquatic system requires knowledge of its natural variation. The goal of this study explored natural variation in the lake fish communities of the northern Bruce Peninsula, which may act as a reference condition for other studies. The results of this study indicated there has been a shift towards more small-bodied, native species present in the fish communities, potentially a result of beaver activity in the area. A second goal was to calculate gear sampling efficiencies to enable the design of efficient monitoring protocols for fish communities in small, shallow lakes. It was concluded that a wide variety of gears are required to assess the fish species composition in a lake. Fine-mesh hoops were the most effective gear; however, saturation was never obtained for boat electrofishing; therefore, additional research is required to determine effectiveness relative to the fine-mesh hoop net.

Whitebark pine (Pinus albicaulis) is declining across its range due to disturbances such as mountain pine beetle and white pine blister rust. In this thesis, I assess the response and vulnerability of whitebark pine ecosystems to multiple stressors and disturbances at the northern edge of P.albicaulis range in the Coastal Mountains of British Columbia, Canada. Both the compositional change over time of overstory and understory communities as well as vegetation spatial patterns suggest that different sites or ecosystem types housing whitebark pine may differ in their response to disturbance and stress. Surveys conducted ~ 20 years apart indicate that overstory community change differed between site types following the decline of P. albicaulis over time, while the understory did not change significantly. The spatial pattern of overstory species and understory communities also indicates that site type may be important in determining forest change under ongoing disturbance to whitebark pine. / Forest Biology and Management