Species invasions are regarded as one of the most serious threats to biodiversity and native ecosystems and our ability to predict and quantify the impacts of invasive species has been an arduous task. Since the 1840s, the Laurentian Great Lakes have experienced an exponential increase in the number of identified invasive species. The most recent, Hemimysis anomala, is a littoral freshwater mysid native to the Ponto-Caspian region of Eastern Europe. They have been identified in all of the Great Lakes (except Lake Superior), the St. Lawrence River downstream to Québec City, and inland lakes in New York State and have the potential to destabilize energy flow in aquatic food webs. Using stable isotopes of carbon (13C) and nitrogen (15N), I evaluated nearshore food web structure at four sites along Lake Ontario’s north shore spanning a gradient of Hemimysis density to determine: 1) if dominant nearshore food web pathways change seasonally, and 2) whether fish exhibit a dietary shift towards consumption of Hemimysis. Also, the effects of Hemimysis consumption on the growth of yellow perch (Perca flavescens) were quantified using bioenergetics modeling and four predictive feeding scenarios simulating Hemimysis incorporation into yellow perch diets. My results suggest Hemimysis are being incorporated into diets of round gobies, alewife and small yellow perch, which has resulted in a trophic lengthening of the food web. As Hemimysis populations continue to establish and stabilize, fish may incorporate this species into their diets at a higher rate. Based on the bioenergetic modeling, the incorporation of Hemimysis into the diets of yellow perch will have a negative impact on their growth. These negative impacts on fish growth will likely be exacerbated when the limited seasonal availability of Hemimysis, patchy distribution and predator avoidance behaviours, are considered. These results have implications surrounding the sustainability of the Great Lakes fishery as Hemimysis will likely increase competition with young fish for food and fish consumption of this new invasive may lead to reduced fish growth. / Thesis (Master, Biology) -- Queen's University, 2012-04-03 23:04:18.612

Comprendre l'organisation de la biodiversité, notamment la distribution et l'abondance des espèces, est une question centrale en écologie. De par son caractère dynamique et parce qu'elle est distribuée à tous les niveaux du vivant, la compréhension des mécanismes sous-jacents permettant sa création et son maintien inclue nécessairement une composante temporelle et spatiale et implique des processus écologiques et évolutifs. Les grottes sous-marines constituent un habitat tout indiqué pour les étudier, car leurs conditions environnementales particulières suggèrent des mécanismes de maintien de la biodiversité particulièrement actifs. De plus, leur caractère naturellement fragmenté permet une différenciation plus aisée des processus agissant à différentes échelles spatiales. Par leur abondance, tant en terme d'espèces que d'individus, les mysidacés cavernicoles en Méditerranée, représentent de ce fait un bon modèle d'étude de ces mécanismes. À l'échelle locale de la parcelle d'habitat, l'étude de l'écologie trophique des cinq espèces de mysidacés cavernicoles (Hemimysis margalefi, H. speluncola, H. lamornae mediterranea, Siriella gracilipes, Harmelinella mariannae) a permis de mettre en évidence l'importance des stratégies alimentaires dans leur maintien. En effet, ces espèces persistent et coexistent non seulement grâce à un partage classique et spatial des ressources et des sites de nourrissage, mais aussi parce que certains sites de nourrissage importants se trouvent à l'extérieur des grottes sous-marines. / Understanding processes of biodiversity creation and maintenance is a central question in ecology. Because biodiversity is dynamic and distributed across all levels of life, identifying underlying mechanisms necessarily takes into account temporal and spatial scales and involves ecological as well as evolutionary processes. Underwater caves are particularly appropriate to address such a question. Indeed, the harsh environmental conditions of this habitat suggest active mechanisms of biodiversity maintenance. In addition, the highly fragmented nature of this habitat facilitates the distinction between the spatial scales at which processes may operate. In the Mediterranean, the high diversity and abundance of cave-dwelling mysids may help identifying the underlying processes that govern biodiversity distribution. At the scale of a habitat patch, the trophic ecology of the main five cave-dwelling mysids (Hemimysis margalefi, H. speluncola, H. lamornae mediterranea, Siriella gracilipes, Harmelinella mariannae) reveals that persistence and coexistence are allowed by trophic strategies such as classical and spatial resource partitioning. In addition, some of the important feeding sites are located outside caves in the productive euphotic zone. This is of particular importance since mysids can bring organic matter from the outside into the caves by way of circadian migrations. This transfer of organic matter can be important in contributing to the persistence of other cave-dwellers.