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There are numerous examples of how exotic insect pests and pathogens have altered the dominance of native tree species and the ecological processes and function related to those species. While targeted species may persist in a functionally altered state via vegetative sprouting, the widespread decimation of a species can have dramatic direct and indirect consequences for organisms in multiple trophic levels. Devastation due to alien insect herbivores poses the greatest threat to native insect larvae that specialize on the impacted host species. The loss of pollinators whose larvae feed on impacted species and provide services for native plants may also be a serious but yet undocumented indirect threat of these exotic invasions. The disruption of mutualistic relationships between native species will have negative consequences for those species and could potentially benefit exotic species. In the southeastern US, laurel wilt disease (LWD) is impacting numerous species in the Lauraceae family, with the majority of cases observed on Persea borbonia, a common sub-canopy tree found in many Coastal Plain habitats. This species is also known to be the primary larval host of the palamedes swallowtail (Papilio palamedes). While infection rates and crown dieback are catastrophically high (>90%), basal resprouting is a common response in P. borbonia. The exotic Cinnamomum camphora is the only Lauraceae species that has shown resistance to LWD and could benefit from opportunities to replace P. borbonia and other Lauraceae species threatened by LWD. The primary objectives of this study were four fold: 1) to quantify P. borbonia sprouting responses in the field and greenhouse and determine the effect of P. borbonia removal on the composition and abundance of woody and herbaceous plant species in the understory layer, 2) to test the relative suitability of C. camphora as an alternative larval host for P. palamedes, 3) to determine the reliance of the Platanthera ciliaris on P. palamedes for successful pollination and the relative availability of alternative long-tongued pollinators, and 4) to forecast how disease-induced shifts in the relative abundance of native (P. borbonia) and exotic (C. camphora) fruit may alter patterns of consumption and subsequent dispersal of C. camphora by birds. The field component (Grand Bay National Estuarine Research Reserve (GBNERR), Jackson County, MS) of chapter two involved the removal of P. borbonia main stems to mimic the impacts of LWD which resulted in a significant increase (~50%) in light transmission. All treated individuals produced sprouts and the size and number of sprouts was positively related to initial tree size. Following the removal of P. borbonia from treatment plots, Ilex vomitoria showed the greatest increase in basal area after two years. Both woody seedlings and herbaceous plants showed no significant trends in composition and/or abundance over time. In the greenhouse (Southern Illinois University, Carbondale, IL), the stem and leaf biomass of vegetative sprouts was significantly greater in a high-nutrient treatment. Light treatments had no effect on sprout production. Results from chapter two suggest that the loss of P. borbonia from the canopy layer may have little direct effect on plant community dynamics. In addition, I found that sprout production is vigorous in P. borbonia and the capacity to persist and tolerate future disturbances may be enhanced on more nutrient-rich sites. In chapter three, I used laboratory experiments and field observations to compare larval performance and adult female preference of P. palamedes between C. camphora and P. borbonia foliage. My results indicate moderate survivorship on C. camphora (46%) compared to P. borbonia (87%) and there were no differences in first and fourth instar growth rates between treatments. Fourth instars consumed less C. camphora foliage than P. borbonia, but metabolic efficiency did not differ between treatments. In the field and laboratory, I found no oviposition preference for C. camphora relative to P. borbonia. While females laid eggs on C. camphora during laboratory trials, the same number of eggs was also laid on inanimate objects. I conclude that C. camphora is suitable for larval development but host-switching to this species by P. palamedes will be primarily constrained by oviposition behaviors. In chapter four, I monitored pollinator visitation and measured nectar spur lengths of P. ciliaris flowers and proboscis lengths of its floral visitors (at GBNERR). Papilio palamedes was the primary visitor (44 visits) but Phoebis sennae was also observed (4 visits). There were no significant differences among P. ciliaris nectar spurlength and the proboscis lengths of P. palamedes and P. sennae. Fruit set was 55 ± 10.8% with access to pollinators and 0% on bagged inflorescences (pollinators excluded). Although I found a positive relationship between visitation and inflorescence size, there was no such pattern in fruit set, indicating that fruit set was not limited by pollinator visitation within the range of visitation rates I observed. Phoebis sennae may provide supplemental pollination service but is likely constrained by habitat preferences that do not always overlap with those of P. cilaris. Although additional observations are needed, my results suggest that expected LWD-induced declines of P. palamedes will threaten the reproductive success and persistence of P. ciliaris populations. In chapter five, I investigated redundancy between C. camphora and P. borbonia with respect to fruit characteristics (physical and chemical) and selectivity by frugivorous birds (at GBNERR). Across two winter survey periods I observed fruit removal from artificial infructescences. I manipulated background species upon which displays were hung (Myrica cerifera and Triadica sebifera) and the accessibility of the displays. Using motion-activated cameras I confirmed foraging bouts on both P. borbonia and C. camphora fruits by three bird species (Dumetella carolinensis, Turdus migratorius, and Catharus guttatus). There was no significant difference in selectivity between fruit types during year one of my surveys but there was a significant preference for C. camphora in year two, which coincided with significantly lower mean daily temperatures. Background tree species and accessibility had no apparent effect on fruit preference. Total polyphenols and pulp:seed ratio were significantly higher in C. camphora fruit. I conclude that the fruits of C. camphora and P. borbonia represent nearly substitutable resources for native birds. However, native species may prefer C. camphora fruit in times of energetic stress. The decline of P. borbonia will likely increase the consumption and dispersal of C. camphora fruits. Additional studies are required to determine if such changes could ultimately increase the distribution and abundance of this exotic species. Combined, the chapters of this dissertation present substantial empirical evidence for the potential multi-trophic level impacts of an exotic plant disease. While it remains unclear how dramatic these impacts will be, the approach used here is vital for understanding and mitigating the long-term ecological effects of species/disease invasions.

Background : Old fields are abandoned agricultural areas that are undergoing secondary succession. A variety of factors influence the assembly, invasibility, and species turnover during secondary succession in old fields. Old fields are important ecological research locations as an increasing amount of agricultural land is abandoned worldwide. Objectives : 1) To determine if exotic and native "invaders" display differences in invasion success in an old field, and 2) To observe how native and exotic species abundances change over the course of secondary succession under predictable disturbance regimes and resource levels with regards to the Core-Satellite Species (CSS) hypothesis. Methods : An old field located in southern Illinois subject to three levels of fertilization (control, annually fertilized, and fertilized every 5 years) crossed with three levels of mowing treatments (control, spring mowed, and spring/fall mowed) established in 1996 was used to test objectives Seedlings of C3 grasses (native and exotic) were planted within one fertilizer treatment to compare invasion success. Species composition data (species occurrence and abundance at three heights) in all blocks were previously collected from 1996 to 2002 and the sample plots were resampled in 2013. Species sampled in 2013 were assigned to core or satellite categories per the CSS hypothesis. Results : Invading exotic seedlings had higher survivorship than invading native seedlings from the same functional group within the same fertilizer level, and added fertilizer increased seedling survivorship. The number of core and satellite species varied early after experiment establishment in 1996 but has since leveled off, and the ratio of exotic to native species cover at heights <1m ratio was affected by an interaction between mowing treatment and time. The species occupancy distribution of all species in 2013 was not bimodally distributed, but the occupancy distribution of exotic species in 2013 was bimodally distributed.The community composition of the plots varied among blocks, but was affected by an interaction between fertilizer treatment and mowing. Conclusions : Exotic invading grass seedlings in a successional community were relatively more successful than native invading grass seedlings. However, overall survivorship of all invading grass seedlings was low, a typical finding in grasslands. The identity of core and satellite species continued to fluctuate through time following 17 years of secondary succession. Resource availability and disturbance regime affects on community composition throughout secondary succession, and may result in many alternative stable states. This research supports the `CSS' and `parallel dynamics' hypotheses and indicates that presence of exotic species within a community does not necessarily facilitate invasion by new exotic species.

nÃo hà / In the present work we performed a study and characterization of benthic macrofauna of the intertidal fringe of PecÃm beach between the years 2006 and 2011 in order to obtain information about the taxonomic diversity of species and deepen knowledge about the ecology of these organisms in the face of new environmental conditions imposed by the deployment of Marine Terminal of Port of PecÃm. Seventy-one taxa belonging to seven taxonomic groups: Porifera, Cnidaria, Mollusca, Annelida (Polychaeta), Arthropoda (Crustacea), Echinodermata and Chordata were listed. Six species of marine benthic invertebrates introduced: the bivalve mollusc Isognomon bicolor, Donax gemmula and Heterodonax bimaculatus, the crustacean Decapoda Charybdis hellerii and the polychaete Phragmatopoma caudata were listed. The species Phragmatopoma caudata, Donax gemmula and Heterodonax bimaculatus were classified as cryptogenic and Isognomon bicolor and Charybdis hellerii as exotic detected in the natural environment. Heterodonax bimaculatus is first recorded in the state of CearÃ, extending its distribution along the Brazilian coast. Specific preferences of benthic macrofauna in relation to the variability of substrates were found. This fact influences the composition and distribution of taxa, has been identified a greater number of taxonomic groups (seven) in consolidated substrate when compared to taxonomic groups (three) identified in the unconsolidated substrate. There were no significant changes in the composition of local benthic macrofauna when compared to other coastal regions of the state. The quantitative fluctuations observed in populations seem to be related to a response of organisms to coastal dynamics, indicating an adaptive process of species to new environmental conditions of the area. It was observed a decrease in the average percentage of coverage of organisms in consolidated substrate, and there were no significant differences in the average number of organisms in unconsolidated substrate between the years 2008 and 2011. With reference to the collect frequency (monthly, bimonthly and quarterly) was observed that the average percentage of coverage of organisms in consolidated substrate and the average amount of organisms in unconsolidated substrate showed no significant differences among the three study periods during the years 2008 and 2011. The quantitative and qualitative data obtained in this study suggest that the introduced species in the intertidal fringe PecÃm beach have not, so far, caused significant impacts on local benthic macrofauna, although they may be considered as a potential threat to the structure of these communities. Shipping accomplished through the Marine Terminal of Port of PecÃm seems to be the vector responsible for the introduction of new species in local macrozoobenthos. / No presente trabalho foi realizado o levantamento e carac-terizaÃÃo da macrofauna bentÃnica da faixa entremarÃs da praia do PecÃm, no perÃodo de 2006 a 2011, com a finalidade de obter informaÃÃes sobre a diversidade taxonÃmica das espÃcies e aprofundar o conhecimento sobre a ecologia desses organismos frente Ãs novas condiÃÃes ambientais impostas pela implantaÃÃo do Terminal PortuÃrio do PecÃm. Foram identificados 71 tÃxons pertencentes a 7 grupos taxonÃmicos: Porifera, Cnidaria, Mollusca, Annelida (Polychaeta), Arthropoda (Crustacea), Echinodermata e Chordata. Como espÃcies introduzidas foram identificados os moluscos bivalves Isognomon bicolor, Donax gemmula e Heterodonax bimaculatus, o crustÃceo decÃpoda Charibdys hellerii e o poliqueta Phragmatopoma caudata. As espÃcies Phragmatopoma caudata, Donax gemmula e Heterodonax bimaculatus foram classificadas como criptogÃnicas e Isognomon bicolor e Charibdys hellerii como exÃticas detectadas em ambiente natural. Heterodonax bimaculatus à registrado pela primeira vez para o estado do CearÃ, ampliando sua distribuiÃÃo na costa brasileira. Foram constatadas preferÃncias especÃficas da macrofauna bentÃnica com relaÃÃo à variabilidade dos substratos o que influencia na composiÃÃo e distribuiÃÃo dos tÃxons, tendo sido identificada uma maior quantidade de grupos taxonÃmicos (7) no substrato consolidado quando comparada aos grupos taxonÃmicos (3) identificados no substrato inconsolidado. NÃo foram observadas alteraÃÃes significativas na composiÃÃo da macrofauna bentÃnica local quando comparada com a de outras localidades costeiras do estado. As flutuaÃÃes quantitativas observadas nas populaÃÃes parecem estar relacionadas a uma resposta dos organismos à dinÃmica costeira, indicando um processo adaptativo das espÃcies Ãs novas condiÃÃes ambientais da Ãrea. Foi verificado um decrÃscimo no percentual mÃdio de cobertura dos organismos no substrato consolidado, nÃo tendo sido observado diferenÃas significativas na quantidade mÃdia de organismos no substrato inconsolidado entre os anos de 2008 e 2011. Com relaÃÃo à periodicidade de coleta (mensal, bimestral e trimestral) observou-se que o percentual mÃdio de cobertura de organismos no substrato consolidado e a quantidade mÃdia de organismos no substrato inconsolidado nÃo apresentaram diferenÃas significativas entre os trÃs perÃodos analisados durante os anos de 2008 e 2011. Os dados quantitativos e qualitativos obtidos nesse estudo sugerem que as espÃcies introduzidas na faixa entremarÃs da praia do PecÃm nÃo tÃm, atà o momento, causado impactos significativos na macrofauna local, embora possam ser consideradas como uma potencial ameaÃa à estrutura dessas comunidades. O transporte marÃtimo realizado atravÃs do Terminal PortuÃrio do PecÃm parece ser o vetor responsÃvel pela introduÃÃo de novas espÃcies no macrozoobentos local.

Espécies exóticas invasoras são consideradas uma das maiores ameaças à biodiversidade, à saúde humana, aos bens e recursos humanos. E, por isso, seu enfrentamento envolve uma ampla gama de instituições atuantes e instrumentos legais. Objetivando contribuir para a formulação e a implementação de uma política pública de enfrentamentos das espécies exóticas invasoras no território brasileiro, o presente estudo foi conduzido a partir de uma análise de dados secundários, que incluiu documentos governamentais, publicações científicas e da legislação aplicável a fim de demonstrar a tese de que os atuais problemas socioambientais, dentre eles as bioinvasões, materializam os desafios do enfrentamento da complexidade dos mesmos, cujas respostas demandam ações articuladas capazes de integrar os conhecimentos técnico-científicos, a legislação aplicável e o arcabouço institucional, sem negligenciar a participação pública dos atores sociais envolvidos no processo de formulação e implementação da política pública. Os resultados indicam que o Brasil vive um cenário de risco ambiental devido a inexistência de ações integradas de enfrentamento do problema. A análise comparada da estrutura brasileira com a de outros três países (África do Sul, Estados Unidos da América e Nova Zelândia) permite constatar que fatores como dimensão do território, estrutura governamental de enfrentamento do problema, coerência entre o arcabouço legal e institucional e disponibilidade de informações científicas coerentes são em conjunto importantes para o sucesso das respostas nacionais ao problema, mas isoladamente não são capazes de explicar tal sucesso. A comparação reforça a tese sobre a importância da retroalimentação da tríade formada pelo conhecimento científico, arcabouço institucional e estrutura jurídica para a resposta às bioinvasões. Os avanços científicos deveriam ser catalisadores do aprimoramento da legislação, que para ser eficiente precisaria prover as instituições de sólidos instrumentos de atuação. Ao aprimorar as suas legislações, os países necessariamente precisariam observar as funções que estes instrumentos cumprem sobre outros aspectos e setores da sociedade e as limitações impostas pela convivência global gerida a partir de acordos internacionais. Como observado a partir da análise do Convention on Biological Diversity e do International Plant Protection Convention, acordos internacionais trouxeram importantes avanços à capacidade brasileira de enfrentamento das bioinvasões. Mas, eles também podem limitar a atuação nacional, especialmente no que diz respeito a adoção de medidas preventivas mais rigorosas. Já uma análise comparada das Políticas Nacionais de Meio Ambiente, de Recursos Hídricos e Agrícola permitiu a identificação de alguns pontos domésticos importantes na formulação e na implementação de uma política de enfrentamento das bioinvasões, dentre os quais estacam-se: a ampla inclusão de atores afetos ao tema, a instalação de arenas de discussão que incorporem as múltiplas visões e dimensões do tema e a integração dos avanços científicos aos instrumentos normativos e aos sistemas operacionais de implantação das políticas. Conclui-se afirmando que, apesar dos avanços científicos, legais e institucionais no enfrentamento das bioinvasões, há notável desarticulação entre estes componentes. E, mais do que instituir uma política pública através de um instrumento legal, deveria ser priorizada a integração efetiva dos supracitados elementos para que se assegure a consistência das ações e a eficiência prática dessa política. / Invasive exotic species are considered one of the greatest threats because they can affect simultaneously biodiversity and human health, property and resources. Therefore, efforts in confronting such species engage a wide range of institutions and legal instruments. In order to contribute to the formulation and implementation of public policies to confront invasive exotic species in the Brazilian territory, this study analyzed secondary data such as government documents, scientific publications and legal instruments, aims to demonstrate the thesis that actual socioenvironmental problems, among them bioinvasions, demands articulated actions capable to integrating technical-scientific knowledge, the applicable legislation and the institutional framework, without neglecting public participation of social actors involved in the process of formulation and implementation of public policy. Results point that Brazil is going through an environmental risk scenario due to the lack of integrated actions to confront the problem. The comparative analysis between the Brazilian structure and that of three other countries (South Africa, United States of America and New Zealand) shows that factors such as size of territory, governmental structure to confront the problem, coherence between the legal and institutional framework and the availability of scientific information jointly are important to the success of national responses to the problem, but individually are not able to explain such success. This comparison reinforces the theory about the importance of integration of scientific knowledge, institutional framework and legal structure for an effective response to bioinvasions. Scientific advances should be catalysts of improvements to legal acts, which in order to be efficient should provide institutions with structured action instruments. In order to improve its legislation, a country needed observe the roles such instruments have on other aspects and sectors of society and the limitations imposed by global coexistence managed by international agreements. Analyses of the Convention on Biological Diversity and International Plant Protection Convention show that international agreements brought important advances to Brazilian capacity to confront bioinvasions. However, such international agreement may limit national acts, especially regarding the adoption of more stringent preventive measures. Additionally, a comparative analysis between Environmental, Water Resources and Agricultural National Policies has allowed the identification of some important domestic points in the formulation and implementation of a public policies to confront bioinvasions, including: wide inclusion of actors involved with the theme, establishment of arenas of discussion that incorporate multiple views and dimensions of the theme and integration of scientific advances to regulatory instruments and operating systems in the implementation of the policies. In conclusion, despite advances in scientific, legal and institutional confrontation of bioinvasions, there is remarkable disconnectivity between these components. Thus, besides the establishment of public policies through legal instruments, the effective integration of these components should be prioritized to ensure consistency of action and efficient practice of such policies.

Espécies exóticas invasoras são consideradas uma das maiores ameaças à biodiversidade, à saúde humana, aos bens e recursos humanos. E, por isso, seu enfrentamento envolve uma ampla gama de instituições atuantes e instrumentos legais. Objetivando contribuir para a formulação e a implementação de uma política pública de enfrentamentos das espécies exóticas invasoras no território brasileiro, o presente estudo foi conduzido a partir de uma análise de dados secundários, que incluiu documentos governamentais, publicações científicas e da legislação aplicável a fim de demonstrar a tese de que os atuais problemas socioambientais, dentre eles as bioinvasões, materializam os desafios do enfrentamento da complexidade dos mesmos, cujas respostas demandam ações articuladas capazes de integrar os conhecimentos técnico-científicos, a legislação aplicável e o arcabouço institucional, sem negligenciar a participação pública dos atores sociais envolvidos no processo de formulação e implementação da política pública. Os resultados indicam que o Brasil vive um cenário de risco ambiental devido a inexistência de ações integradas de enfrentamento do problema. A análise comparada da estrutura brasileira com a de outros três países (África do Sul, Estados Unidos da América e Nova Zelândia) permite constatar que fatores como dimensão do território, estrutura governamental de enfrentamento do problema, coerência entre o arcabouço legal e institucional e disponibilidade de informações científicas coerentes são em conjunto importantes para o sucesso das respostas nacionais ao problema, mas isoladamente não são capazes de explicar tal sucesso. A comparação reforça a tese sobre a importância da retroalimentação da tríade formada pelo conhecimento científico, arcabouço institucional e estrutura jurídica para a resposta às bioinvasões. Os avanços científicos deveriam ser catalisadores do aprimoramento da legislação, que para ser eficiente precisaria prover as instituições de sólidos instrumentos de atuação. Ao aprimorar as suas legislações, os países necessariamente precisariam observar as funções que estes instrumentos cumprem sobre outros aspectos e setores da sociedade e as limitações impostas pela convivência global gerida a partir de acordos internacionais. Como observado a partir da análise do Convention on Biological Diversity e do International Plant Protection Convention, acordos internacionais trouxeram importantes avanços à capacidade brasileira de enfrentamento das bioinvasões. Mas, eles também podem limitar a atuação nacional, especialmente no que diz respeito a adoção de medidas preventivas mais rigorosas. Já uma análise comparada das Políticas Nacionais de Meio Ambiente, de Recursos Hídricos e Agrícola permitiu a identificação de alguns pontos domésticos importantes na formulação e na implementação de uma política de enfrentamento das bioinvasões, dentre os quais estacam-se: a ampla inclusão de atores afetos ao tema, a instalação de arenas de discussão que incorporem as múltiplas visões e dimensões do tema e a integração dos avanços científicos aos instrumentos normativos e aos sistemas operacionais de implantação das políticas. Conclui-se afirmando que, apesar dos avanços científicos, legais e institucionais no enfrentamento das bioinvasões, há notável desarticulação entre estes componentes. E, mais do que instituir uma política pública através de um instrumento legal, deveria ser priorizada a integração efetiva dos supracitados elementos para que se assegure a consistência das ações e a eficiência prática dessa política. / Invasive exotic species are considered one of the greatest threats because they can affect simultaneously biodiversity and human health, property and resources. Therefore, efforts in confronting such species engage a wide range of institutions and legal instruments. In order to contribute to the formulation and implementation of public policies to confront invasive exotic species in the Brazilian territory, this study analyzed secondary data such as government documents, scientific publications and legal instruments, aims to demonstrate the thesis that actual socioenvironmental problems, among them bioinvasions, demands articulated actions capable to integrating technical-scientific knowledge, the applicable legislation and the institutional framework, without neglecting public participation of social actors involved in the process of formulation and implementation of public policy. Results point that Brazil is going through an environmental risk scenario due to the lack of integrated actions to confront the problem. The comparative analysis between the Brazilian structure and that of three other countries (South Africa, United States of America and New Zealand) shows that factors such as size of territory, governmental structure to confront the problem, coherence between the legal and institutional framework and the availability of scientific information jointly are important to the success of national responses to the problem, but individually are not able to explain such success. This comparison reinforces the theory about the importance of integration of scientific knowledge, institutional framework and legal structure for an effective response to bioinvasions. Scientific advances should be catalysts of improvements to legal acts, which in order to be efficient should provide institutions with structured action instruments. In order to improve its legislation, a country needed observe the roles such instruments have on other aspects and sectors of society and the limitations imposed by global coexistence managed by international agreements. Analyses of the Convention on Biological Diversity and International Plant Protection Convention show that international agreements brought important advances to Brazilian capacity to confront bioinvasions. However, such international agreement may limit national acts, especially regarding the adoption of more stringent preventive measures. Additionally, a comparative analysis between Environmental, Water Resources and Agricultural National Policies has allowed the identification of some important domestic points in the formulation and implementation of a public policies to confront bioinvasions, including: wide inclusion of actors involved with the theme, establishment of arenas of discussion that incorporate multiple views and dimensions of the theme and integration of scientific advances to regulatory instruments and operating systems in the implementation of the policies. In conclusion, despite advances in scientific, legal and institutional confrontation of bioinvasions, there is remarkable disconnectivity between these components. Thus, besides the establishment of public policies through legal instruments, the effective integration of these components should be prioritized to ensure consistency of action and efficient practice of such policies.

Marine seaweeds constitute one of the most productive plant systems known on Earth and a rich fauna including juvenile fish and crustaceans is dependent on the habitats they form. Human influence on marine costal ecosystems has resulted in large scale changes to the abundance and distribution of species, where species introductions constitute an obvious part. The aims of this thesis were to 1) explore how non-native seaweeds impact on ecosystem functions (primary production and decomposition), and 2) study how interactions between non-native seaweeds and native communities affect invasion success. I used a combination of laboratory assays, outdoor mesocosms and field experiments. Paper I and II revealed that the impact on ecosystem functions were substantially different depending on the identity of the invader. The highly successful non-native red alga Heterosiphonia japonica had a large effect on community productivity. Due to the rapid growth of the invader, the primary production increased by more than four times in mixed species communities with the invader compared to  communities with only native species. In contrast, the morphologically similar and equally successful non-native red alga Bonnemaisonia hamifera grew slowly and had no effect on community production. But B. hamifera produces a potent defense compound that deters native herbivores and reduces the growth of micro-organisms. As a direct or indirect effect of this chemical defense, the litter from B. hamifera decomposed considerably slower compared to native seaweed litter. Rapid growth and defense against predation are likely important in explaining how the two invaders have become successful in the invaded range. These results show that traits related to invasion success may determine impacts on native communities. Paper III shows that the rapidly growing invader H. japonica is avoided as food by native herbivores, which likely enables the invader to survive during colder seasons with sub-optimal growth conditions.  In paper IV I found that competition from the native brown alga Fucus vesiculosus decreased growth of the non-native congener Fucus evanescens. Native herbivores caused more damage to the native competitor but it did not relieve F. evanescens from competitive pressure. Several native brown algae grow in the niche of F. evanescens, which may explain why the species only is growing sparingly in the invaded range. The results indicate that competition with native seaweeds have potential to reduce the success of non-native seaweeds in the new range. In summary, this thesis shows that non-native seaweeds differ strongly in their effect on ecosystem functions. Knowledge of which traits are present among abundant non-native species and how these traits relates to different effects may enable us to gain a better understanding of invasion impacts on native communities. The thesis also highlights that competitive interactions can be of importance for invasion success in seaweed communities. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p> / Alien-native trophic interactions: consequences for invasion success and ecosystem effects of invasions

As introduções de espécies exóticas têm significantemente modificado a estrutura das comunidades levando à extinção muitas espécies nativas. A crescente invasão, nas águas doces brasileiras pelo gastropoda Melanoides tuberculata, de origem africano-asiática, é preocupante. No presente estudo foram analisados diversos aspectos referentes ao ciclo de vida, à tolerância a variáveis abióticas e à sensibilidade a substâncias tóxicas de referência e aos sedimentos contaminados de três reservatórios do estado de São Paulo (Rasgão, Barra Bonita e Promissão). Testou-se a eficácia do látex de Euphorbia splendens e de Asclepias curassavica como moluscicida. Os moluscos foram coletados em tanques de piscicultura, em Pirassununga, SP, e cultivados em laboratório, determinando-se a taxa de crescimento e a tolerância à temperatura e à salinidade. Os resultados evidenciaram que esta espécie tolera temperaturas entre 16 e 37 'graus' C e tem ampla tolerância à salinidade (0,968 a 17,138 g/L). As 'CL IND.50' para substâncias de referência foram: 0,734 mg/L para o dicromato de potássio; 0,701 g/L para o cloreto de potássio e de 9,053 g/L para o cloreto de sódio. Em relação ao látex de plantas tóxicas, obtiveram-se 'CL IND.50' entre 2,924 ppm e 3,308 ppm para Euphorbia splendens, enquanto o látex de Asclepias curassavica não foi tóxico até o limite máximo de 20,0 ppm. Os sedimentos dos reservatórios de Barra Bonita e Promissão (rio Tietê) não foram tóxicos, enquanto o sedimento de Rasgão foi extremamente tóxico a este molusco. Concluiu-se que a alta tolerância de M. tuberculata a elevadas temperaturas e à salinidade corroboram sua ampla e rápida dispersão pelas águas doces tropicais e que o látex de Euphorbia splendens pode ser utilizado como moluscicida natural em baixas concentrações em programas integrados de controle da invasão desta espécie invasora / The introduction of exotic species have marcantly altered the structure of communities, leading to the extinction of many native species. The progressive invasion of brazilian freshwaters by the gastropoda Melanoides tuberculata, with afro-asian origin, is quite worrying at the moment. In the present study some aspects of the life cycle of M. tuberculata, its tolerance to abiotic variables and its sensibility to both toxic reference substances and contaminated sediments from São Paulo state reservoirs (Barra Bonita, Promissão and Rasgão) were evaluated. It was also tested the efficiency of the latex of Euphorbia splendens and Asclepias curassavica as natural moluscicids. Moluscs were collected from fish ponds in Pirassununga, SP, and cultured in the laboratory, in order to determine their individual growth rate and tolerance to temperature and salinity. The results have evidenced that this species can tolerate temperatures between 16 and 37 degrees C and have a wide tolerance to salinity (0.968 to 17.138 g/L). The 'LC IND.50' for reference substances were: 0.734 mg/L for potassium dichromate; 0.701 g/L for potassium chloride and 9.053 g/L for sodium chloride. In relation to the latex of toxic plants, a 'LC IND.50' of 2.924 ppm and 3.308 ppm was found for Euphorbia splendens, whereas the latex of Asclepias curassavica was not toxic up to the maximum of 20.0 ppm tested. Sediments from the reservoirs Barra Bonita and Promissão (rio Tietê) were not toxic, whereas the sediment of Rasgão was extremely toxic to this molusc. It was concluded that M. tuberculata can tolerate high temperatures and salinity, what is in accordance to its wide and rapid dispersion throughout tropical waters, and that the latex of Euphorbia splendens can be used as natural moluscicid in low concentrations in integrated control programs of this invader species

A construção dos reservatórios implica em alterações de caráter social, econômico e biológico, que podem interferir de maneira espacial e/ou temporal sobre o ecossistema. Neste contexto, as características das comunidades ícticas têm sido utilizadas para avaliação da degradação ambiental, por serem sensíveis indicadoras de estresses diretos ou indiretos de todo ecossistema. Desta forma, com o intuito de analisar a comunidade íctica do reservatório de Bariri segundo a composição, a diversidade, a dominância das espécies e os aspectos reprodutivos das mesmas, fez-se necessário: 1. Calcular o índice de diversidade (Shannon), a riqueza e a abundância das trinta e sete espécies de peixes coletadas; 2. Aplicar o índice ponderal de dominância; 3. Determinar a estrutura das populações de peixes em relação à composição em tamanho, sexo e proporção sexual; 4. Determinar a relação peso x comprimento e os fatores de condição das espécies; 5. Estabelecer uma escala de maturação e verificar, através da curva de maturação, o período reprodutivo e o tamanho do menor indivíduo em 1ª maturação para cada espécie dominante; 6. Identificar quais as espécies exóticas presentes neste sistema e se a introdução de Plagioscion squamosissimus e Cichla cf. monoculus, em especial, exerciam algum impacto sobre a dinâmica populacional das demais espécies e 7. Verificar quais os fatores ambientais que propiciaram o sucesso reprodutivo das espécies dominantes e de Plagioscion squamosissimus e Cichla cf. monoculus. Assim sendo, concluiu-se que a diversidade ictiofaunística revelou homogeneidade entre as quatro épocas de coleta e que as espécies parecem sofrer influência direta de algumas variáveis limnológicas. Verificou-se ainda, que a ictiofauna é composta por seis espécies dominantes, as quais foram classificadas em três estádios de maturação gonadal, possibilitando verificar que o crescimento era do tipo isométrico para todas as espécies dominantes, sem dimorfismo sexual. Até o presente momento não se pode considerar que, para este reservatório, a introdução das espécies Plagioscion squamosissimus e Cichla cf. monoculus tenham causado efeito aparente sobre as espécies nativas, diminuindo o tamanho da população destas ou ainda alterando a estrutura etária das demais espécies. / The construction of reservoirs cause changes of social, economic and biological alterations, that can interfere spatially and/or temporally upon the ecosystem. In this context, the characteristics of fish communities have been used in order to evaluate environmental degradation, because they are good indicators of direct and indirect stresses in the whole ecosystem. Therefore, aiming to analyze the fish community of Bariri reservoir regarding the species composition, diversity and dominance of species and also their reproductive aspects, it was necessary: 1. Calculate the diversity index (Shannon), the species richness and the abundance of the 37 species collected; 2. Apply the ponderal dominance index; 3. To determine fish population structure regarding size structure, sex and sex ratio; 4. To determine length-weight relationships and their condition factor; 5. Establish a scale of maturation and to verify using the maturation curve, the reproductive period and the minimum individual size in the first reproduction, for each dominant species; 6. Identify which are the exotic species present in the system and to verify if the introduction of Plagioscion squamosissimus and Cichla cf. monoculus, especially had some impact on the population dynamics of other species, and 7. Verify which environmental factors have determined the reproductive success of the dominant species and Plagioscion squamosissimus and Cichla cf. monoculus. It was concluded that fish diversity was homogeneous among the four sampling periods and that the species seem to suffer the direct influence of some limnological variables. It was also verified that the fish community was composed by six dominant species, which were classified in three gonad maturation stages, allowing to verify that growth was isometric for all the dominant species, without sexual dimorphism. Up to now, for this reservoir, it was not possible to consider that the introduction of the species Plagioscion squamosissimus and Cichla cf. monoculus had an apparent effect on the native species of fish, decreasing their population size or changing the age structure of the other species.