The central theme of this dissertation research addresses fundamental ecological questions about community assembly (which species are found in a given place). This includes our understanding of the role of abiotic stresses in environments, species invasions, system resistance to invasion and the impacts of invaders. The natural, model aquatic community found in leaves of the pitcher plant, Sarracenia purpurea, was used to experimentally test the effects of different biotic interactions, abiotic factors, and characteristics of different species on the success of invasion by a new species in a community. These factors were looked at individually as well as in combination, and their relative impacts on resident community dynamics were also examined. The molecular technique of metagenomics (16s rRNA clone libraries) was incorporated into this work in order to determine the effects of the introduction of consumers with different characteristics on food web structure and species diversity. These experiments revealed that for this system: 1) it is the number of invaders, not their body size, that is important for invasion success, 2) the effects of invasion are dependent upon which species invade, 3) invasion impacts on the resident community depend on whether species are competitors or prey for the invader, 4) invaders in the middle of the food web that are better competitors and arrive in large numbers will have the greatest success, 5) the presence of a top predator controls how the community is affected when species in other levels invade, and 6) the availability of resources changes the susceptibility of a community to invaders. These results are important for understanding and predicting species invasion success and how to mitigate the spread and impact of invaders. By incorporating modern genomics tools, this dissertation research also re-examined results from prior experiments using this system and verified that community level responses observed in experiments using only common culturable bacteria reflected the response of the entire community and that the generalizations found among studies of this community are robust.