A food web was constructed for a boreal-forest dominated national park in south-eastern Sweden, called Tyresta national park and its surrounding nature reserve. Due to increasing threats to mammalian species and their critical role in the food web mammals were used as the outset of the food web, and from there branching out to taxa trophically interacting with mammals directly and indirectly. The outset of the food web was constructed using available inventory data, focusing on mammals. From inventory data and 53 interaction sources, consisting of mostly primary literature a food web was created that includes 32 mammalian taxa, six bird families, five invertebrate taxa, fish, amphibians, fungi, reptiles, detritus and 9 different basal plant taxa. The results of the literature review was that the most consumed staple taxon of all were hexapods, with it being a staple food for 15 taxa, six of them being bats preying mainly on dipterans. There are a wide variety of ways that interspecific competition could come to affect taxa in the study area, for example through intraguild predation, increased dietary breadth or avoidance, or a combination of these. This method could serve as a complement to existing food webs or the construction of new ones in a cheaper, less intrusive and less time-consuming way, albeit missing local adaptations. The constructed food web structure and findings of interspecific competition in Tyresta can be used for further analyzing certain links or branching the web out even further, with increased depth or quantification of certain taxon.

Invasive plants can displace native species, deteriorate native forest, and change plant communities and ecosystem functions. Native plant populations are fundamentally impacted by invasive species because of the interactions between invasive species and native plants. This study focuses on understanding the extent, mechanisms and consequences of interaction between a non-indigenous invader Ailanthus altissima and its functionally similar native species Robinia pseudoacacia in the Mid-Appalachian region, from an individual scale to a regional scale. These two subject species are common and coexist in early-successional eastern deciduous forest. The interactions between these two common species are important to community structure and canopy tree regeneration. To address the type and extent of interactions of these two species, a greenhouse experiment utilizing various species proportions, nutrient levels and seed sources was performed. In addition, a common-garden experiment with various species densities and proportions over three consecutive growing seasons was performed in a more natural condition than that of the greenhouse experiment. We found at the seedling stage, the dominant interaction was competition, and R. pseudoacacia was the winner both above- and belowground. The allelopathic compounds of A. altissima may have inhibited nodulation of R. pseudoacacia. Ailanthus altissima seedlings from its native region had slightly stronger competitive abilities compared with the seedlings from its invaded range. In the common garden experiment, R. pseudoacacia plants grew quicker than A. altissima, but A. altissima inhibited the growth of R. pseudoacacia by interspecific competition. The negative impact of A. altissima on R. pseudoacacia became larger as time progressed. To assess the community-level consequences of the two species, we conducted a forest mapping and a complete target-tree-based forest survey, and analyzed regional-scale data from the Forest Inventory Analysis Data Base. The two target species were significantly associated with themselves and with each other. Community species composition and diversity were significantly different across sites. A negative impact of both species on the understory community diversity and tree regeneration at the neighborhood scale was detected; while at a regional level, tree diversity in the FIA plots with either A. altissima or R. pseudoacacia was higher than the reference plots. / Ph. D.

Chionochloa, a genus of snow tussock grasses native to New Zealand, exhibits pronounced mast seeding. Chionochloa suffers very high levels of pre-dispersal flower and seed predation by three main insects: Eucalyptodiplosis chionochloae, a cecidomyiid midge, which is formally described here; Megacraspedus calamogonus, a gelechiid moth and Diplotoxa similis, a chloropid fly. Seven species of parasitoids that attack these seed predators were discovered. Four species parasitize M. calamogonus (one tachinid fly and three hymenopteran wasps), one parasitizes D. similis (Hymenoptera: Eulophidae) and two parasitize E. chionochloae, (a pteromalid wasp Gastrancistrus sp. and a platygastrid wasp Zelostemma chionochloae, which is given a formal description here). The abundance, predation levels by each of the insect species, and interactions between all the organisms in the community were studied across three elevations at Mount Hutt over three summer seasons. M. calamogonus was most abundant at 450 m altitude during all three seasons. D. similis was most common at 1070 m altitude, while its predation levels peaked in low flowering seasons and decreased in high seasons. E. chionochloae was abundant in all three altitudes and increased its predation levels with increasing flowering intensity. E. chionochloae was confirmed to use prolonged diapause of at least three years. Prolonged diapause was also confirmed in its two parasitoids. Chionochloa plants were manipulated with various treatments to test the effect on diapause in E. chionochloae and its two parasitoids. Treatments included plant warming, root pruning, gibberellic acid sprayed on the plants and combinations of these treatments. All three insects changed their emergence in response to some treatments and therefore it was suggested that combined with risk-spreading diapause, they may use some predicting to emerge from prolonged diapause. E. chionochloae control their diapause following some of the cues that Chionochloa use for flowering, while Z. chionochloae and Gastrancistrus in some cases follow their host’s cues and in others use similar cues as Chionochloa plants. Emergence or diapause predictions differed across elevations and plant species in all three insect seed/flower predators. E. chionochloae had female-biased sex ratios in different populations even after prolonged diapause. There was week evidence that both parasitoid species are female-biased in the first emergence year and male-biased after more than one year in diapause. Therefore it was suggested that diapause is not more costly for females of E. chionochloae and its parasitoid than for males. Females of all three species were not found to be better predictors (i.e, more likely to respond to treatments by not entering extended diapause) than males. The complex interactions of all the organisms in this web are thought to be sensitive to climate, and it was suggested that the global climate change may alter this sensitive system.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

The observational study on natural regeneration of Norway spruce (Picea abies) was provided during seasons 2010 and 2011 in the windthrow area of High Tatra National Park. The main aim of this master thesis was to describe the distribution pattern in Norway spruce regeneration as well as to estimate the spatial scale, which most preciselly describes the differences in its phenotypic variability. Following step was to determine the relative influence of abiotic and stand factors on the growth characteristics and abundance of spruce seedlings. The Main focus lied on stressing the role of biotic interactions, like intraspecific and interspecific competition, leading to certain discrepancies in the phenotype, as well as in abundance of spruce seedlings.The reponse in variability in spruce traits was recognized at each spatial level. The results showed clear causality between soil moisture and vegetation composition, which both directly modified not only the phenotype of spruce seedlings and plants, but have even influenced their counts on particular stands.

Competition between different species (interspecific competition) is an important factor to consider when estimating population trends, geographic distributions, and management options of species. Many historically common vascular plant species found in agricultural environments have been negatively affected by changes in community composition and in turn, changes in competition pressures. Even so, the relative importance of plant competition in an ecological context is still unclear. In this study I examine the competitive ability of the meadow plant cornflower (Centaurea cyanus L.) when grown together with common oat (Avena sativa) and common poppy (Papaver rhoeas), during a seven-week long growth chamber experiment. Seeds were sown in pots in four different setups; 1) C. cyanus control, 2) C. cyanus + P. rhoeas, 3) C. cyanus + A.sativa, 4) All three species. Six different growth parameters were measured (aboveground dry-weight, belowground dry-weight, root length, leaf area, number of leaves and above/belowground dry-weight ratio). I found that growth rates of C. cyanus were significantly inhibited according to all six growth parameters when C. cyanus competed solely with A. sativa. Competition from P. rhoeas had an insignificant effect on C. cyanus growth in five out of six growth parameters. Finally, I discuss the possibility that historically common meadow plants have declined in abundance in part because of weak competitive abilities, and that rare vascular plant species are negatively affected by growing in proximity with cereal crops.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

This project predominantly investigated the implications of spatial heterogeneity in the ecological processes of competition and infection. Empirical analysis of spatial heterogeneity was carried out using the lepidopteran species Plodia interpunctella. Using differently viscous food media, it was possible to alter the movement rate of larvae. Soft Foods allow the movement rate of larvae to be high, so that individuals can disperse through the environment and avoid physical encounters with conspecifics. Harder foods lower the movement rate of larvae, restricting the ability of individuals to disperse away from birth sites and avoid conspecifics encounters. Increasing food viscosity and lowering movement rate therefore has the effect of making uniform distributed larval populations more aggregated and patchy. Different spatial structures changed the nature of intraspecific competition, with patchy populations characterised by individuals experiencing lower growth rates and greater mortality because of the reduced food and space available within densely packed aggregations. At the population scale, the increased competition for food individuals experience in aggregations emerges as longer generational cycles and reduced population densities. Aggregating individuals also altered the outcome of interspecific competition between Plodia and Ephestia cautella. In food media that allowed high movement rates, Plodia had a greater survival rate than Ephestia because the larger movement rate of Plodia allowed it to more effectively avoid intraspecific competition. Also the faster growth rate, and so larger size, of Plodia allowed it to dominate interspecific encounters by either predating or interfering with the feeding of Ephestia. In food that restricts movement, the resulting aggregations cause Plodia to experience more intraspecific encounters relative to interspecific, reducing its competitive advantage and levelling the survival of the two species. Spatial structure also affected the dynamics of a Plodia-granulosis virus interaction and the evolution of virus infectivity. Larval aggregation forced transmission to become limited to within host patches, making the overall prevalence of the virus low. However potentially high rates of cannibalism and multiple infections within overcrowded host aggregations caused virus-induced mortality to be high, as indicated by the low host population density when virus is presented. Also aggregated host populations cause the evolution of lower virus infectivity, where less infective virus strains maintain more susceptible hosts within the aggregation and so possess a greater transmission rate. The pattern of variation in resistance of Plodia interpunctella towards its granulosis virus was found using two forms of graphical analysis. There was a bimodal pattern of variation, with most individuals exhibiting either low or high levels of resistance. This pattern was related to a resistance mechanism that is decreasingly costly to host fitness.

Chionochloa, a genus of snow tussock grasses native to New Zealand, exhibits pronounced mast seeding. Chionochloa suffers very high levels of pre-dispersal flower and seed predation by three main insects: Eucalyptodiplosis chionochloae, a cecidomyiid midge, which is formally described here; Megacraspedus calamogonus, a gelechiid moth and Diplotoxa similis, a chloropid fly. Seven species of parasitoids that attack these seed predators were discovered. Four species parasitize M. calamogonus (one tachinid fly and three hymenopteran wasps), one parasitizes D. similis (Hymenoptera: Eulophidae) and two parasitize E. chionochloae, (a pteromalid wasp Gastrancistrus sp. and a platygastrid wasp Zelostemma chionochloae, which is given a formal description here). The abundance, predation levels by each of the insect species, and interactions between all the organisms in the community were studied across three elevations at Mount Hutt over three summer seasons. M. calamogonus was most abundant at 450 m altitude during all three seasons. D. similis was most common at 1070 m altitude, while its predation levels peaked in low flowering seasons and decreased in high seasons. E. chionochloae was abundant in all three altitudes and increased its predation levels with increasing flowering intensity. E. chionochloae was confirmed to use prolonged diapause of at least three years. Prolonged diapause was also confirmed in its two parasitoids. Chionochloa plants were manipulated with various treatments to test the effect on diapause in E. chionochloae and its two parasitoids. Treatments included plant warming, root pruning, gibberellic acid sprayed on the plants and combinations of these treatments. All three insects changed their emergence in response to some treatments and therefore it was suggested that combined with risk-spreading diapause, they may use some predicting to emerge from prolonged diapause. E. chionochloae control their diapause following some of the cues that Chionochloa use for flowering, while Z. chionochloae and Gastrancistrus in some cases follow their host’s cues and in others use similar cues as Chionochloa plants. Emergence or diapause predictions differed across elevations and plant species in all three insect seed/flower predators. E. chionochloae had female-biased sex ratios in different populations even after prolonged diapause. There was week evidence that both parasitoid species are female-biased in the first emergence year and male-biased after more than one year in diapause. Therefore it was suggested that diapause is not more costly for females of E. chionochloae and its parasitoid than for males. Females of all three species were not found to be better predictors (i.e, more likely to respond to treatments by not entering extended diapause) than males. The complex interactions of all the organisms in this web are thought to be sensitive to climate, and it was suggested that the global climate change may alter this sensitive system.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Right after the arising of the Panama isthmus, the family Canidae colonized South America, around 2.6-2.4 million years ago. Although canids radiation in South America is recent, this region holds the largest canid diversity in the world, with more than 10 extant species. This great diversity is also notable when dealing with the ecomorphological variation of these animals. The maned-wolf (Chrysocyon brachyurus), a large omnivore, and the bush-dog (Speothos venaticus), a small hypercarnivore, are the extreme exemples of this variation. Such shape diversity can be potentially explained by both abiotic, such as climate, and biotic factors, like competition. These factors may have contributed for stabilizing the south-american canids community. Thus, this study aimed to investigate what drives this ecomorphological amplitude, as well as to understand how can similar species coexist when overlapping their distributional ranges, such as the crab-eating fox (Cerdocyon thous), which has sympatric areas with Lycalopex vetulus and L. gymnocercus, two foxes ecologically similar to Cerdocyon thous. To answer these questions, 431 especies were photographed in nine South-American museums. Through geometric morphometric procedures, it was possible to quantify the phenotypic variation of eight canid species (Atelocynus microtis, C. thous, C. brachyurus, L. culpaeus, L. griseus, L. gymnocercus, L. vetulus e S. venaticus) throughout their geographical range and then test the contribution of biotic and abiotic factors driving this variation. The evidences presented in this study suggest C. thous alters its shape and body size when in sympatry with two Lycalopex species, pattern described by character displacement , which is when similar species shift their phenotype in order to minimize competition. Besides, C. thous also follows the Bergmann s rule, which predicts that body size increases at larger latitudes. When considering the canid community as a whole, climate was identified as the main factor contributing to phenotypic variation in these animals. Competition has a weaker impact in south-american canids skull morphology, although it may have played a larger role in the past, when the ecomorphological diversity in the subcontinent was even larger. / Logo após a emergência completa do istmo do Panamá, a família Canidae colonizou a América do Sul, há, aproximadamente, 2.6-2.4 milhões de anos atrás. Embora a radiação dos canídeos seja recente na América do Sul, esta região compõe a maior diversidade atual de espécies desta família no mundo, com mais de 10 espécies viventes. Esta grande biodiversidade também é notável na variação ecomorfológica destes animais. Exemplo disso são os dois extremos desta variação: o lobo-guará (Chrysocyon thous), um animal onívoro de grande tamanho corporal; e o cachorro-vinagre (Speothos venaticus), espécie hipercarnívora de pequeno porte. Tamanha diversidade de formas pode potencialmente ser explicada tanto por fatores abióticos, como o clima, e bióticos, como a competição. Ambos os fatores podem ter contribuído para a estabilização da comunidade de canídeos sul-americana. Por isso, este estudo se propôs a investigar o que impulsionou esta amplitude ecomorfológica, bem como entender como espécies mais similares coexistem quando em sobreposição distribucional, como o graxaim-do-mato (Cerdocyon thous), que possui área simpátrica a Lycalopex vetulus e L. gymnocercus, duas raposas ecologicamente similares a Cerdocyon thous. Para tanto, 431 espécimens foram fotografados em nove museus da América do Sul. Através de procedimentos de morfometria geométrica, foi possível quantificar a variação fenotípica de oito espécies de canídeos (Atelocynus microtis, C. thous, C. brachyurus, L. culpaeus, L. griseus, L. gymnocercus, L. vetulus e S. venaticus), ao longo de sua distribuição geográfica, e então testar a contribuição dos fatores bióticos e abióticos nesta variação. As evidências deste estudo sugerem que C. thous altera sua forma e tamanho corporal quando em simpatria com as duas espécies de Lycalopex, padrão descrito pelo deslocamento de caráter , quando espécies semelhantes alteram seu fenótipo em simpatria, a fim de minimizar a competição. Além disso, C. thous também segue a regra de Bergmann, que prevê um aumento de tamanho corporal com o aumento da latitude. Ao considerar a comunidade de canídeos como um todo, o clima foi identificado como o fator que mais contribuiu para a variação fenotípica destes animais. A competição, por sua vez, tem um impacto mais fraco na morfologia do crânio dos canídeos sul-americanos, embora possa ter tido uma maior contribuição no passado, quando a diversidade ecomorfológica no subcontinente era ainda maior.