Invasive exotic species threaten the biodiversity and function of native ecosystems. Existing models, attempting to predict and control successful invaders, often emphasize isolated stages of in their life history and fail to formalize interactions between exotic species and recipient environments. In order to elucidate key mechanisms in the success of select invaders, I investigated the role of dispersal, establishment, proliferation, and persistence in their threat to natural areas. Focusing on Riding Mountain National Park, Manitoba, Canada, I integrated the native climatic range and biological traits of 251 exotic vascular plants reported inside and outside the park. Based on their climatic range in Europe, 155 among 174 exotic plant species absent from the Park were predicted to establish within its boundaries; among these, 40 clonal perennials were considered the highest threat to the Park’s biodiversity. Focusing on smooth brome (Bromus inermis Leyss.), a Eurasian perennial, threatening the structure and function of native prairies throughout the Great Plains, I extended my research to investigate the role of dispersal, establishment, proliferation, and persistence in characterizing its threat to the endemic diversity of northern fescue prairies, protected within Riding Mountain National Park. Patterns of smooth brome invasions were contingent on the type of propagules dispersed. The shallow dispersal gradient of individual florets combined with the steeper gradient of panicles and spikelets suggested that smooth brome is capable of simultaneously invading along dense fronts as well as by establishing isolated foci. While low correlations between the number of dispersed seeds and their recruitment suggested post-dispersal transport, seedling establishment remained contingent on prairie diversity. Seedling biomass increased with declining plant diversity, however, its impact depended on the availability of soil nitrogen. As a result, disturbed areas, preserving the root function of native plants, resisted smooth brome establishment. Even though low nitrogen contributed to a decline in seedling biomass, physiological integration between ramets facilitated their vegetative proliferation in low resource environments. Despite its rapid establishment and proliferation, smooth brome productivity declined at the center of invading clones. Although field and greenhouse observations failed to implicate soilborne pathogens, reasons for the observed decline remain unresolved. My research demonstrates that while Riding Mountain National Park and other natural areas in western Canada will continue to be impacted by exotic plants, integrating key stages in their life history provides an important conceptual framework in predicting their threat to natural areas and prioritizing management. / October 2008

Invasive exotic species threaten the biodiversity and function of native ecosystems. Existing models, attempting to predict and control successful invaders, often emphasize isolated stages of in their life history and fail to formalize interactions between exotic species and recipient environments. In order to elucidate key mechanisms in the success of select invaders, I investigated the role of dispersal, establishment, proliferation, and persistence in their threat to natural areas. Focusing on Riding Mountain National Park, Manitoba, Canada, I integrated the native climatic range and biological traits of 251 exotic vascular plants reported inside and outside the park. Based on their climatic range in Europe, 155 among 174 exotic plant species absent from the Park were predicted to establish within its boundaries; among these, 40 clonal perennials were considered the highest threat to the Park’s biodiversity. Focusing on smooth brome (Bromus inermis Leyss.), a Eurasian perennial, threatening the structure and function of native prairies throughout the Great Plains, I extended my research to investigate the role of dispersal, establishment, proliferation, and persistence in characterizing its threat to the endemic diversity of northern fescue prairies, protected within Riding Mountain National Park. Patterns of smooth brome invasions were contingent on the type of propagules dispersed. The shallow dispersal gradient of individual florets combined with the steeper gradient of panicles and spikelets suggested that smooth brome is capable of simultaneously invading along dense fronts as well as by establishing isolated foci. While low correlations between the number of dispersed seeds and their recruitment suggested post-dispersal transport, seedling establishment remained contingent on prairie diversity. Seedling biomass increased with declining plant diversity, however, its impact depended on the availability of soil nitrogen. As a result, disturbed areas, preserving the root function of native plants, resisted smooth brome establishment. Even though low nitrogen contributed to a decline in seedling biomass, physiological integration between ramets facilitated their vegetative proliferation in low resource environments. Despite its rapid establishment and proliferation, smooth brome productivity declined at the center of invading clones. Although field and greenhouse observations failed to implicate soilborne pathogens, reasons for the observed decline remain unresolved. My research demonstrates that while Riding Mountain National Park and other natural areas in western Canada will continue to be impacted by exotic plants, integrating key stages in their life history provides an important conceptual framework in predicting their threat to natural areas and prioritizing management.

Invasive exotic species threaten the biodiversity and function of native ecosystems. Existing models, attempting to predict and control successful invaders, often emphasize isolated stages of in their life history and fail to formalize interactions between exotic species and recipient environments. In order to elucidate key mechanisms in the success of select invaders, I investigated the role of dispersal, establishment, proliferation, and persistence in their threat to natural areas. Focusing on Riding Mountain National Park, Manitoba, Canada, I integrated the native climatic range and biological traits of 251 exotic vascular plants reported inside and outside the park. Based on their climatic range in Europe, 155 among 174 exotic plant species absent from the Park were predicted to establish within its boundaries; among these, 40 clonal perennials were considered the highest threat to the Park’s biodiversity. Focusing on smooth brome (Bromus inermis Leyss.), a Eurasian perennial, threatening the structure and function of native prairies throughout the Great Plains, I extended my research to investigate the role of dispersal, establishment, proliferation, and persistence in characterizing its threat to the endemic diversity of northern fescue prairies, protected within Riding Mountain National Park. Patterns of smooth brome invasions were contingent on the type of propagules dispersed. The shallow dispersal gradient of individual florets combined with the steeper gradient of panicles and spikelets suggested that smooth brome is capable of simultaneously invading along dense fronts as well as by establishing isolated foci. While low correlations between the number of dispersed seeds and their recruitment suggested post-dispersal transport, seedling establishment remained contingent on prairie diversity. Seedling biomass increased with declining plant diversity, however, its impact depended on the availability of soil nitrogen. As a result, disturbed areas, preserving the root function of native plants, resisted smooth brome establishment. Even though low nitrogen contributed to a decline in seedling biomass, physiological integration between ramets facilitated their vegetative proliferation in low resource environments. Despite its rapid establishment and proliferation, smooth brome productivity declined at the center of invading clones. Although field and greenhouse observations failed to implicate soilborne pathogens, reasons for the observed decline remain unresolved. My research demonstrates that while Riding Mountain National Park and other natural areas in western Canada will continue to be impacted by exotic plants, integrating key stages in their life history provides an important conceptual framework in predicting their threat to natural areas and prioritizing management.

Made available in DSpace on 2014-07-29T16:21:17Z (GMT). No. of bitstreams: 1 Dissertacao parte 1 Thaisa Sala Michelan.pdf: 38222 bytes, checksum: 2f8d3a6cb8df8f1c42d663b0b5323ef6 (MD5) Previous issue date: 2011-05-28 / Exotic species represent strong threats to biodiversity. This concern is especially valid in freshwater ecosystems due to their high biodiversity and the highest rates of extinction, compared with terrestrial and marine ecosystems. The increasing habitat complexity provided by the presence of macrophytes may partially explain the high diversity of aquatic ecosystems. However, depending on the density and other particular characteristics of these plant, the diversity may be negatively affected. In this context, Urochloa subquadripara, a species native to Africa, is an aquatic macrophyte weed occurring in various natural and artificial aquatic ecosystems in America. In a small scale, the occurrence of this exotic species increases with reducing natives species richness; however, in a large scale U. subquadripara invades sites with more richness of native species. This controversy is typical of observational studies in invasion biology and it demand experiments to test effects of abiotic and biotic resistance on the invasive potential of this exotic. Accordingly, two experiments were conducted in order to test the following hypotheses: (i) the regeneration and colonization of U. subquadripara decreases with increasing time of exposure to dry, (ii) fragments of the apical part of this species, when compared with those of the basal part, have higher viability and colonization potential (first experiment) and (iii) the invasiveness of aquatic environments by U. subquadripara is negatively influenced by the richness and abundance of native species (second experiment). Our results supported all of our hypotheses: U. subquadripara showed high resistance to desiccation, and the fragments of the apical part were those which had higher viability and colonization potential. In addition, both richness and abundance of native species affected negatively the invasive potential of this exotic macrophyte. The second experiment demonstrated that the effect of richness and abundance limited the development of U. subquadripara, although such effect was not sufficient to prevent the invasion of macrophyte communities by this species. Based on these results, it appears that the population growth of U. subquadripara is greater in disturbed sites, mainly those affected by drought, which in general, have lower abundance and diversity of native species. / Espécies exóticas representam fortes ameaças à biodiversidade. Essa preocupação é especialmente válida em ecossistemas aquáticos continentais em função da elevada biodiversidade e das maiores taxas de extinção, quando comparados com ecossistemas terrestres e marinhos. O aumento da complexidade dos habitats promovido pela presença de macrófitas aquáticas pode explicar em parte a elevada diversidade dos ecossistemas aquáticos. No entanto, dependendo das densidades e de outras características espécies-específicas dessas plantas, a diversidade pode ser negativamente afetada. Nesse contexto, Urochloa subquadripara, espécie nativa da África, é uma macrófita aquática infestante de vários ecossistemas aquáticos naturais e artificiais na América. Em pequena escala espacial, a ocorrência dessa exótica aumenta com a redução do número de espécies nativas, já em grande escala U. subquadripara invade locais com maior riqueza de espécies nativas. Essa controvérsia é típica de estudos observacionais em biologia de invasões sendo necessária a realização de experimentos para testar efeitos da resistência abiótica e biótica sobre o potencial invasor de exóticas. Nesse sentido, foram realizados dois experimentos, com o objetivo de testar as seguintes hipóteses: (i) a regeneração e colonização de U. subquadripara diminui com o aumento do tempo de exposição a seca; (ii) os fragmentos da parte apical dessa espécie, quando comparados com aqueles da parte basal, apresentam maior viabilidade e potencial de colonização (primeiro experimento) e (iii) a invasibilidade de ambientes aquáticos por U. subquadripara é influenciada negativamente pela riqueza e abundância de espécies nativas (segundo experimento). De modo geral, todas as hipóteses foram aceitas: U. subquadripara apresentou alta resistência a dessecação, sendo que os fragmentos da parte apical foram os que apresentaram maior viabilidade e potencial de colonização e tanto a riqueza como a abundância de espécies afetaram negativamente o potencial invasor dessa exótica. Esse último experimento demonstrou que, apesar de limitar o desenvolvimento de U. subquadripara, o efeito da riqueza e abundância de nativas não é suficiente para impedir a invasão de comunidades de macrófitas por essa espécie. Com base nesses resultados, infere-se que o crescimento populacional de U. subquadripara é maior em locais perturbados, principalmente por distúrbios como a seca que, em geral, também apresentam menor abundância e diversidade de espécies nativas.