Habitat fragmentation can influence the genetics of a population through the direct loss of genetic diversity, and by the genetic processes that occur as a result of small remnant populations or the geographic isolation of populations. I examined the population genetics of two woodland amphibian species in localities with different land-use histories. The wood frog (Rana sylvatica) and the red-backed salamander (Plethodon cinereus) use the same general habitat but differ with respect to a few key life-history characteristics relating to dispersal. I then compared between species the relative influence each land-use scenario had on the population genetic structure. I found that habitat fragmentation affected the population genetics of the two amphibians and did so differently for each species. The differential population genetic response of these two amphibians to habitat fragmentation reinforces the important role of life-history characteristics in how the genetic structure of a population is shaped over time.

This thesis examines the ecological consequences of sewage disposal in aquatic ecosystems. Sewage simultaneously represents a form of enrichment and a source of stress to a receiving system. Enrichment effects dominate when sewage loading does not exceed the capacity of the system to assimilate waste, as is presently the case in the St. Lawrence River. We developed a method to quantify the assimilation of sewage-derived organic matter by riverine biota, then used this method to examine the pathways by which sewage enhances secondary production in the St. Lawrence. We showed that the relative importance of dissolved nutrients and particulate organic matter to the river food web is to a large degree dictated by the physical and biological characteristics of the local environment. The effects of this enrichment on the receiving water community were also influenced by habitat characteristics. Analysis of body size distributions revealed that only the largest organisms had higher densities at enriched sites, and that the identity of these organisms depended on habitat structure. Densities of smaller organisms were controlled by a combination of habitat characteristics and feeding interactions. This pattern was consistent with food web models of top-down (consumer) control. At each trophic level, relatively invulnerable (large) prey achieved higher densities, whereas densities of more vulnerable (small) prey were controlled by their predators. Finally, we synthesized the ideas outlined above to predict how conditions in the St. Lawrence will change in the future as a result of lower water levels. More extensive macrophyte cover, slower current, and warmer temperatures in a shallower St. Lawrence will all enhance the ability of the system to physically retain and biologically process sewage nutrients, but will also increase the likelihood of negative effects such as anoxia.

No description available.

“What I have tried to do in this and in all my writing on the early days of this country is what the artist does when he paints a sketch of a Canadian scene or a Canadian person. I have tried to select something that is beautiful or significant or interesting or essential to an understanding of ourselves. I have tried to tell the stories of personalities, men and women who have by their human qualities, aspirations, and activities, given substance to our history, whose loves and hates and fears and achievements have been woven into the very fabric of our Canadian consciousness. I have tried to say, as the painter says, ‘here is something I think you would like to know,’ ‘here is something that has significance’ or ‘here is something that may evoke your love or pride or indignation I as the case may be.” (IO:x) This, in very simple terms, has been my aim here - to paint a picture, or rather a series of pictures of the North Shore, past and present, from the viewpoint of the human geographer. I make no claim to be a historian, nor to have encompassed the full range of material available. Rather, I have selected from the accounts of yesteryear certain aspects which have an attraction for me personally, in the hope that these might also be of interest to others. In brief, I have attempted to write an academic treatise which will yet prove acceptable to the ‘reading public.‘ [...] / fr

This research examined how an invasive macrofouling organism, the Eurasian zebra mussel (Dreissena polymorpha), alters benthic communities in a riverine ecosystem. Controlled field experiments using artificial substrates showed that macroinvertebrate abundance is significantly enhanced within Dreissena beds, and that the physical habitat provided by mussel shells has a greater impact on macroinvertebrate abundance than biological factors (e.g., food provided by mussel biodeposits). Data collected at field sites before and after the establishment of dense Dreissena colonies suggested that these colonies alter macroinvertebrate communities on hard substrates primarily by enhancing populations of deposit-feeding organisms (e.g., amphipod crustaceans) and predators (e.g., flatworms), and by displacing fauna that are poorly adapted to interstitial substrate (e.g., large gastropods, net-spinning caddisfly larvae). Freshwater sponges were the only organisms found to compete successfully with Dreissena for hard substrate; sponge overgrowth caused significant local mortality of zebra mussels at all sites where sponges were abundant. / The capacity for Dreissena to displace native freshwater mussels (Family Unionidae) in the St. Lawrence River was examined over a four year period by quadrat sampling at selected sites. Dreissena preferentially colonized unionid mussels in the river. Mean infestation loads (number of zebra mussels per unionid mussel) in the St. Lawrence were 10-100 times lower than in the Great Lakes,.but resulted in similar high mortality. Severe declines in unionid species richness and abundance occurred in areas of the river that supported dense Dreissena populations ($>$4,000 mussels/m$ sp2).$ Analysis of data from the Great Lakes-St. Lawrence River system suggests that mass mortality and extirpation of unionid populations typically occurs within 4-5 years following initial colonization of unionids by Dreissena, and that Dreissena infestation will increase the future tate of extinction of North American unionids by nearly 10-fold.

“What I have tried to do in this and in all my writing on the early days of this country is what the artist does when he paints a sketch of a Canadian scene or a Canadian person. I have tried to select something that is beautiful or significant or interesting or essential to an understanding of ourselves. I have tried to tell the stories of personalities, men and women who have by their human qualities, aspirations, and activities, given substance to our history, whose loves and hates and fears and achievements have been woven into the very fabric of our Canadian consciousness. I have tried to say, as the painter says, ‘here is something I think you would like to know,’ ‘here is something that has significance’ or ‘here is something that may evoke your love or pride or indignation I as the case may be.” (IO:x) This, in very simple terms, has been my aim here - to paint a picture, or rather a series of pictures of the North Shore, past and present, from the viewpoint of the human geographer. I make no claim to be a historian, nor to have encompassed the full range of material available. Rather, I have selected from the accounts of yesteryear certain aspects which have an attraction for me personally, in the hope that these might also be of interest to others. In brief, I have attempted to write an academic treatise which will yet prove acceptable to the ‘reading public.‘ [...] / fr

No description available.

“What I have tried to do in this and in all my writing on the early days of this country is what the artist does when he paints a sketch of a Canadian scene or a Canadian person. I have tried to select something that is beautiful or significant or interesting or essential to an understanding of ourselves. I have tried to tell the stories of personalities, men and women who have by their human qualities, aspirations, and activities, given substance to our history, whose loves and hates and fears and achievements have been woven into the very fabric of our Canadian consciousness. I have tried to say, as the painter says, ‘here is something I think you would like to know,’ ‘here is something that has significance’ or ‘here is something that may evoke your love or pride or indignation I as the case may be.” (IO:x) This, in very simple terms, has been my aim here - to paint a picture, or rather a series of pictures of the North Shore, past and present, from the viewpoint of the human geographer. I make no claim to be a historian, nor to have encompassed the full range of material available. Rather, I have selected from the accounts of yesteryear certain aspects which have an attraction for me personally, in the hope that these might also be of interest to others. In brief, I have attempted to write an academic treatise which will yet prove acceptable to the ‘reading public.‘ [...] / fr

Using SCUBA and an in situ method of quantifying substrate characteristics, I describe patterns of zebra mussel (Dreissena polymorpha) distribution along the St. Lawrence and Hudson Rivers and in Oneida Lake, New York, and develop empirical models for their abundance. Calcium-poor waters originating from rivers draining the Canadian Shield resulted in a lack of zebra mussel along the north shore of the St. Lawrence River east of Montreal until Portneuf despite an abundance of suitable substrate. Calcium concentrations of 15 mg/L or less were found to limit the distribution of zebra mussel. The entire south shore from Cornwall, Ontario to Ile d'Orleans, Quebec was colonized by zebra mussel wherever suitable substrate was found. In the Hudson River, along the south shore of the St. Lawrence River and in Oneida Lake variability in density was primarily related to substrate type which explained between 38% and 91% of the variance. Other factors such as Secchi depth, calcium concentration of the water, the presence of crayfish, native unionid abundance and the maximum width of the river at the site increased the amount of explained variance across the different systems. The influence of substrate type on zebra mussel density and the predictions of the model were also tested using data from the literature, where substrate type explained 75% of the variability in density. The scatter of the literature data above the predictions of the empirical model suggests that North American zebra mussel populations may continue to grow before reaching equilibrium levels. While water chemistry parameters may be useful predictors of the presence or absence of zebra mussel in a given water body, physical factors play a far greater role in determining local abundance.

No description available.