Dentre as ameaças causadas pealas mudanças climáticas, é esperado um aumento na frequência e na magnitude de eventos climáticos extremos. Portanto, é de vital importância identificar características da comunidade que confiram estabilidade aos processos ecossistêmicos. Por meio de três experimentos buscamos explorar essas intrincadas relações entre alguns aspectos da biodiversidade e a estabilidade ecológica. No primeiro estudo, comparamos a produtividade primária antes e depois de uma inundação em comunidades sintéticas com diferentes valores de riqueza de espécies, diversidade e composição funcional. No segundo experimento, investigamos como alterações na intensidade de chuvas (simuladas por meio de interceptadores) afetaram os atributos funcionais, diversidade e processos ecossistêmicos de um campo nativo sob diferentes frequências de desfolhação. O terceiro estudo, consistiu em um experimento com manipulação da riqueza de espécies por meio de remoções, onde analisamos o efeito da diversidade de espécies na estabilidade nos níveis de organização de comunidade (colonizações e extinções) e ecossistema (variação na produtividade primária). Atributos funcionais e outras características da comunidade (riqueza e composição) afetaram e foram afetadas pelos distúrbios. A relação diversidade-estabilidade apresentou diferentes tendências dependendo da natureza e intensidade do distúrbio. O aumento dos recursos após a inundação favoreceu comunidades mais ricas e aquelas contendo atributos relacionados à aquisição de recursos. Além disso, a frequência de desfolhação não afetou a resposta da vegetação à manipulação de chuva. Estabilidade apresentou tendências opostas dependendo do nível de organização ecológica considerado. Maior substituição 63 de espécies em comunidades mais ricas correspondeu a uma maior estabilidade em 64 processos ecossistêmicos. / Climate change is expected to increase the frequency and magnitude of extreme weather events. It is therefore of major importance to identify the community attributes that confer stability in ecosystem processes facing such events. By means of three experiment-based studies, we aimed to explore how plant community aspects affect ecological stability. In the first study, we compared data on biomass productivity before and after a major flood in synthetic plant communities with different values of species richness, functional diversity and community weighted means of functional traits on different measures of stability. In the second experiment, we investigate how changes in rainfall (simulated by rainout-shelters) alter functional traits and diversity and ecosystem processes of a natural grassland under different defoliation frequencies. The third study consisted on a biodiversity experiment in which we manipulated species richness by removals for studying the effects of species diversity on the stability at the community (colonization and extinction) and ecosystem levels (variation in primary productivity). Functional traits and other community features (richness, composition) affected and were affected by the disturbances. Diversity-stability relationships presented different trends depending on the disturbance nature and intensity. Resource inputs following the flood favoured rich communities and the ones characterized by traits related to resource acquisition. Also, defoliation frequency did not affect the way vegetation responded to rainfall manipulation. Stability showed opposite trends when evaluated at different levels of ecological organization. Higher turnover in rich communities corresponded to increased stability in ecosystem processes.

The ecology behind evolutionary diversification is a well studied area of research, whereas the effects of evolution on ecosystems get little attention. In line with ecological theory, evolutionary diversification of a species could influence different ecosystem aspects such as food web composition, energy flow, nutrient cycling etc. The main objective of this study was to investigate whether two diverging ecotypes (reed and chara) of Asellus aquaticus differ regarding their role in two aquatic ecosystem processes: decomposition of terrestrial leaves and grazing of periphyton. Their role in ecosystem process as well as treatment effects on fitness, measured as growth and survival, were investigated in a laboratory experiment with various levels of intra-specific competition and inter-specific interactions with the amphipod Gammarus pulex. The isopods were collected from two Swedish lakes: Lake Tåkern and Lake Fardume. These two lakes represent different history of ecotype divergence. The experimental design consisted of 2-L aquaria, each providing elm leaves (Ulmus glabra), oak leaves (Quercus roburleaves) and periphyton as food sources. Ten treatments with five replicates were applied for each lake and the experiment lasted for four weeks. The study showed that there was no significant difference between chara and reed ecotype in their functional role. However, the rate of ecosystem processes per individual decreased in competitive interactions. In high density, decomposition per dry weight consumer was low and total algae biomass was high at the end of four weeks due to intra-specific competition. Moreover, ecosystem processes were lowest in inter-specific competition between Gammarus pulex and each ecotype. Present study also shows that ecotypes from the different lakes, having different history, had different responses to mortality and growth.

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